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WO2018179006A1 - Palladium based selenides as highly stable and durable cathode materials in fuel cell for green energy production - Google Patents

Palladium based selenides as highly stable and durable cathode materials in fuel cell for green energy production Download PDF

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Publication number
WO2018179006A1
WO2018179006A1 PCT/IN2018/050168 IN2018050168W WO2018179006A1 WO 2018179006 A1 WO2018179006 A1 WO 2018179006A1 IN 2018050168 W IN2018050168 W IN 2018050168W WO 2018179006 A1 WO2018179006 A1 WO 2018179006A1
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catalyst
metal
acac
acetylacetonate
reaction solution
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PCT/IN2018/050168
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French (fr)
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Sebastian Chirambatte PETER
Saurav Chandra SARMA
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Jawaharlal Nehru Centre For Advanced Scientific Research
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9008—Organic or organo-metallic compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H01M4/8621—Porous electrodes containing only metallic or ceramic material, e.g. made by sintering or sputtering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/923—Compounds thereof with non-metallic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to synthesis of palladium-based chalcogenides. These materials exhibit high stability and have good activity towards oxygen activation and reduction, because of which they are expected to have their application as cathode materials in fuel cell. More particularly, the present invention relates to a method to synthesize palladium based binary and ternary nanomaterials, CoPd 2 Se 2 and Pd 17 Se 15 , and its application as electrocatalyst in the fuel cell. The present invention relates to a synthesis of highly stable and durable nanomaterials with selenium rich surface. The catalyst outperforms the present state-of-the-art material Pt/C and Pd/C in terms of stability and durability. The present disclosure further relates to a unique, one-pot method to synthesize binary and ternary chalcogenides and applications of said nanomaterial as a cathodic electrode material.
  • Fuel cells are receiving growing attention as a viable energy alternative.
  • fuel cells are used to convert chemical energy stored into electrical energy with the production of environmental-friendly by-product in an efficient manner, typically via fuel oxidation and an accompanying oxygen reduction reaction (ORR).
  • ORR oxygen reduction reaction
  • Fuel cells are potential energy sources for everything ranging from small electronics to cars and homes. There are different types of fuel cells in existence today, each with varying chemistry, requirements, and uses.
  • a fuel cell comprises of a fuel electrode (anode), an oxidant electrode (cathode) and an electrolyte.
  • fuel is continuously fed to the anode where it gets oxidized, and oxygen is reduced at the cathode.
  • fuel cell and energy storage devices lack efficient and stable catalysts for such reactions for a long run.
  • designing of a stable catalyst with good activity is a must.
  • prior arts in literature demonstrated comparatively low stability towards ORR.
  • ORR oxygen reduction reaction
  • Pt-based ORR catalysts often have issues with stability during operations at a wide range of operating voltages and harsh electrolytic conditions that the catalyst is subjected to. These voltage ranges can stress both the Pt catalyst and the carbon substrate. Methods to improve the durability of the ORR catalyst and to enhance the reaction activity have been the focus of worldwide research for the past several decades.
  • the catalyst of the invention is capable of catalyzing the reduction of oxygen.
  • the reduction of oxygen may be achieved by exposing the catalyst to the oxygen.
  • the oxygen may be in any suitable form, such as pure oxygen gas or preferably as an oxygen-containing gas mixture, most preferably air (which may include dry or partially dried or treated air).
  • ORR which takes place at the cathode of a fuel cell can proceed via four or two electron process.
  • the four electron process involves the combination of oxygen with electrons and protons in a single step to produce water.
  • the two electron process consists of two steps; the first of these produces hydrogen peroxide ions as an intermediate and the second converts these to water.
  • the present invention provides a catalyst for a polymer electrolyte fuel cell comprising a metal-based chalcogenide comprising a transition metal and/or a noble metal and a chalcogen.
  • the metal-based chalcogenide is selected from the group comprising of CoPd 2 Se 2 , Pd 17 Se 15 , FePd 2 Se 2 , CoPd 2 Te 2 and compounds listed in Table 2.
  • the catalyst is supported on a support material containing carbon.
  • the support material is selected from carbon black, acetylene black, Vulcan XC-72, activated charcoal, synthetic graphite or natural graphite.
  • the catalyst is a promising cathode material in a polymer electrolyte membrane fuel cell.
  • the catalyst enhances the four- electron reduction process of oxygen.
  • the catalyst has an onset potential and half-wave potential closer to the state-of-the-art material Pd/C.
  • the catalyst is tolerant towards methanol oxidation.
  • the catalyst shows similar tafel slope as Pd/C that is 60 mVdec "1 .
  • the catalyst is used as a cathode material in a polymer electrolyte membrane fuel cell.
  • the electrolyte used in the fuel cell is oxygen-saturated KOH solution.
  • the present invention also provides a polymer electrolyte membrane fuel cell comprising the catalyst as a cathode material, and the electrolyte used in the fuel cell is oxygen- saturated KOH solution.
  • the present invention also provides a one-pot method for synthesizing metal-based chalcogenide nanoparticle comprising:
  • reaction solution (i) mixing one or more metal acetylacetonate (0.1-0.6 atomic percent) or acetate (0.1-0.6 atomic percent) based precursor with a chalcogen precursor (0.1-0.7 atomic percent) in a solvent (20-50 ml) to obtain a reaction solution;
  • step (iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product;
  • the metal acetylacetonate or acetate based precursor is selected from a group comprising of platinum acetylacetonate (Pt(acac) 2 ), platinum acetate (Pt(OAc) 2 ), palladium acetylacetonate (Pd(acac) 2 ), palladium acetate (Pd(OAc) 2 ), cobalt acetylacetonate (Co(acac) 2 ), cobalt acetate (Co(OAc) 2 ), iron acetylacetonate (Fe(acac) 3 ), iron acetate (Fe(OAc) 3 ), nickel acetylactonate (Ni(acac) 2 ), nickel acetate (Ni(OAc) 2 ), copper acetylactonate (Cu(acac) 2 ), copper acetate (Cu(OAc) 2 ), manganese acetylacetonate (M
  • the chalcogen precursor is selected from a group comprising of selenium powder (Se), seleneous acid (H 2 Se0 3 ), sodium selenide (Na 2 Se), sodium telluride (Na 2 Te), sodium sulphide (Na 2 S), thiourea (NH 2 CSNH 2 ) and sodium selenosulphate (Na 2 0 3 SSe).
  • the solvent for the synthesis is selected from a group comprising of octyl amine, oleyl amine, ethylene diamine, ethylene glycol and tetraethylene glycol.
  • the reagent is selected from a group comprising of trioctylphosphine, sodium borohydride (NaBH 4 ) and lithium triethylborohydride (Li(C 2 H 5 ) 3 BH).
  • the metal-based chalcogenide is selected from the group comprising of CoPd 2 Se 2 , Pd 17 Se 15 , FePd 2 Se 2 , CoPd 2 Te 2 and compounds listed in Table 2.
  • the metal-based chalcogenide nanoparticle is having hexagonal or spherical morphology.
  • the metal-based chalcogenide nanoparticle has a stability of 50000 cycles towards ORR with less than 20 mV shift in half- wave potential.
  • the metal-based chalcogenide is CoPd 2 Se 2 nanoparticle and obtained by the process comprising:
  • step (iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product;
  • the metal-based chalcogenide is PdnSeis nanoparticle and obtained by the process comprising: (i) mixing palladium acetylacetonate( Pd(acac) 2 ) (0.1-0.6 atomic percent) with a seleneous acid (H 2 Se0 3 ) (0.-0.7 atomic percent), in a tetraethylene glycol (20-50 ml) to obtain a reaction solution;
  • step (iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product;
  • Figure 1 (a) is a X-ray diffraction pattern (XRD) of ternary chalcogenide CoPd 2 Se 2 . It shows the intensity of the diffraction peak in arbitrary unit versus the angle of diffraction. Major diffraction peaks at 34.16 °, 35.94 °, 39.90 °, 43.66 °, 50.36° and 52.26° correspond to (220), (211), (112), (231), (042) and (060) planes respectively. It corresponds to orthorhombic crystal system with Ibam space group, (b) is a PXRD pattern of binary chalcogenide PdnSe ⁇ .
  • XRD X-ray diffraction pattern
  • FIG. 2 shows (a,b) TEM images of as -synthesized CoPd 2 Se 2 nanoparticles confirming its hexagonal morphology, (c) High-Resolution Transmission Electron Microscopy (HRTEM) images indicating the exposed crystallographic facets, (d) Selected Area Electron Diffraction (SAED) pattern shows the polycrystalline nature of CoPd 2 Se 2 nanoparticles.
  • HRTEM High-Resolution Transmission Electron Microscopy
  • SAED Selected Area Electron Diffraction
  • Figure 3 shows (a,b) TEM images of as-synthesized PdnSe ⁇ nanoparticles showing the aggregated nature of the particles, (c) High-Resolution Transmission Electron Microscopy (HRTEM) images indicating the exposed crystallographic facets, (d) Selected Area Electron Diffraction (SAED) pattern shows the polycrystalline nature of PdnSe ⁇ nanoparticles.
  • Figure 4 shows (a) the FESEM images of CoPd 2 Se 2 nanoparticles. Hexagonal morphology of the nanoparticles can be clearly seen from the images, (b) EDX spectrum of CoPd 2 Se 2 nanoparticles.
  • the inset table represents the composition of individual elements present in the system.
  • Figure 5 shows (a) SEM images of the as-prepared Pd 17 Se 15 , (b) elemental mapping of Pd 17 Se 15 indicates the presence of both the elements. Elemental mapping of individual elements - (c) Se (pink) and (d) Pd (purple), (e) EDX spectrum of Pd 17 Se 15 nanoparticles.
  • the elemental composition of the sample is provided as an inset.
  • Figure 6 shows (i) core level XPS spectra of (a) Co, (b) Pd and (c) Se elements in CoPd 2 Se 2 nanocomposite and (ii) core level XPS spectra of Pd 17 Se 15 nanoparticles. High resolution XPS spectrum of (a) Pd-3 ⁇ 3 ⁇ 4 /2 , Pd-3 ⁇ 3 ⁇ 4 /2 and (b) Se-3 ⁇ i.
  • Figure 7 shows (a) LS V polarization curve at different rpm rate in 0.1 M KOH at a sweep rate of 5 mV/sec, (b) the koutecky-levich plot for CoPd 2 Se 2 /Vulcan nanocomposite at different potentials. The plots are generated from the LSV curves of all the samples tested in oxygen- saturated 0.1 M KOH solution with different rotating speeds, (c) Tafel plot (overpotential plotted vs. logarithm of current density) indicating faster reduction kinetics on hexagonal shaped nanoparticles, and (d) no. of electrons involved in ORR as a function of potential applied.
  • Figure 8 shows (a) LSV polarization curve before and after 50000 cycles in 0.1 M KOH at a sweep rate of 5 mV/sec, (b) Tafel slope comparison before and after ADT showing slight decrease in the Tafel slope value, (c) polarization curve in the presence of 1 M methanol showing almost no effect on the catalyst, and (d) Tafel slope of catalyst in absence and presence of 1 M methanol.
  • Figure 9 shows (a) Polarization curve of Pd 17 Se 15 before and after cycling, (b) CV curve as a function of cycle number showing the removal of Se from the surface due to prolonged cycling, (c) ORR polarization curve showing the negative shift due to exposed Pd sites and (d) tafel slope showing that the same mechanism is being followed before and after cycling.
  • Figure 10 shows (a) the comparison of the present invention with the state-of-the-art material Pd/C and (b) tafel slope of the present invention is similar to that of the state-of- the-art material showing that the present invention follows similar mechanism as that of the Pd/C.
  • Table 1 shows the comparison of the present invention with the state-of-the-art catalyst Pd/C 40 wt%.
  • Table 2 shows that the present invention is not limited to the referred examples but can be extended to the following list of materials.
  • the present invention addresses the issues of problem/drawbacks of the existing processes with the development of low-cost chalcogenide materials with earth abundant and less expensive elements. Moreover, catalysts of the present invention are stable for 50000 electrochemical cycles, highest reported so far for any ORR catalyst. In addition, catalysts of the present invention show activity as good as commercial Pd/C but durability is far better than Pd/C. Unlike many complicated synthesis methods, the present invention provides a facile one-pot synthesis method to synthesize the named catalysts.
  • This invention will be useful in the fabrication of highly efficient and robust fuel cell, which is a renewable and green source of energy.
  • fuel cell is being used as a green source of energy not only in portable devices but also in other stationary systems.
  • the major challenge in the development of the highly efficient fuel cell is the development of highly active and stable electrocatalysts. At the current state, the active catalysts are made of expensive and earth scarce Pt metal with very low stability.
  • Embodiments of the present invention provide a one-pot method to synthesize palladium based binary and ternary chalcogenides for oxygen reduction reaction that offers comparable activity while maintaining exceptional durability and long-term stability.
  • the activity and durability properties of the disclosed ORR catalysts may be due to the preparation methods used and crystal structure of the compound.
  • CoPd 2 Se 2 nanoparticles are synthesized by colloidal synthesis method.
  • Pd(acac) 2 , H 2 Se0 3 and Co(acac) 2 are mixed in oleyl amine in a two-necked RB.
  • Trioctylphosphine is then added to the solution.
  • the RB is then fitted with a condenser, vacuumed and purged with Ar gas. It is then heated for a few hours.
  • the product obtained is repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven.
  • the amount of trioctylphosphine (stabilizing agent) used is 600-1000 ⁇ .
  • the heating is preferably done at 220 °C-250 °C for 2-6 h.
  • the drying is preferably done at 60°C for 6-12 h.
  • Pd 17 Se 15 nanoparticles are synthesized by polyol synthesis method.
  • Pd(acac) 2 (0.09-0.12 mmol) and H 2 Se0 3 (0.1 mmol) are mixed together in TEG (15 ml) in a two-necked RB (50 ml).
  • NaBH 4 40 mg
  • the RB is then fitted with a condenser, vacuumed and purged with Ar gas. It is then heated (220-250°C for 3-6 h).
  • the product obtained is repeatedly washed with hexane- ethanol mixture for several times and then dried in vacuum oven (60°C for 6-12 h).
  • Electrocatalytic evaluation of the prepared catalyst was done using a rotating disc electrode technique on samples both before and after extended use as a catalyst in ORR. Prolonged use here was accomplished by subjecting the catalyst to cyclic voltammetry, which involved cycling 50000 times repeatedly for about one week.
  • the described invention meets the present-day demand of a durable cathode catalyst with good activity for a fuel cell.
  • Methods of preparing the catalyst are also described. It consists of a transition metal and/or a noble metal, and a chalcogenide non-metal.
  • the transition metal is chosen from the group consisting of nickel, cobalt and iron. Particularly, transition metal used in one of the embodiment is cobalt.
  • the noble metal is selected from the group consisting of palladium and platinum.
  • noble metal used in one of the embodiment is palladium.
  • the chalcogen is preferably selected from a group consisting of sulphur, selenium and tellurium.
  • chalcogen used in of the embodiment is selenium.
  • non-noble metal refers to the metals of second and third triads of group VIII of the periodic table namely ruthenium, rhodium, palladium, platinum, osmium and iridium.
  • Chalcogenide refers to the elements of group 16 family in the periodic table with electronegative character.
  • the present invention discloses a cathode catalyst for a polymer electrolyte fuel cell comprising a transition metal and/or a noble metal and a chalcogen.
  • the cathode catalyst for polymer electrolyte membrane fuel cell wherein said alloy catalyst is supported on a support material containing carbon.
  • the catalyst is supported by carbon black, acetylene black, Vulcan XC-72R, activated charcoal, synthetic graphite or natural graphite.
  • present invention provides a method for making a cathode catalyst for a polymer electrolyte fuel cell comprising a transition metal and/or a noble metal and a chalcogen wherein said method comprises one-pot synthesis method.
  • the synthesis method includes heating at a temperature range of 220°C-250°C.
  • the morphology of the nanoparticles/ cathode catalyst obtained by this method can be hexagonal/spherical.
  • the cathode catalyst obtained by this method is active towards ORR.
  • the electrolyte used is oxygen- saturated KOH solution.
  • the cathode catalyst of the present invention has a stability of 50000 cycles towards ORR with less than 20 mV shift in half-wave potential.
  • the catalyst enhances the four-electron reduction process of oxygen.
  • the catalyst has an onset potential and half-wave potential closer to the state-of-the-art material Pd/C.
  • the catalyst is tolerant towards methanol oxidation.
  • the catalyst shows similar tafel slope as Pd/C i.e. 60 mVdec "1 .
  • the catalyst can be used as a cathode material in a fuel cell.
  • the ternary chalcogenide has a molar ratio of transition metal: noble metal: chalcogen as 1:2:2 and the binary chalcogenide has a compositional ratio of noble metal: chalcogenide as 17: 15.
  • the precursor of the transition and the noble metals are preferably present as a metal-organic complex.
  • Preferred ligands are acetylacetonate or acetate.
  • Selenium is preferably present as seleneous acid.
  • Decomposition of the metal organic complex precursors requires high temperature and reductive environment, which is ensured by the use of reducing solvent at high temperature.
  • the preferred solvent for the synthesis includes oleyl amine, ethylene diamine and tetraethylene glycol. Particularly, oleyl amine and tetraethylene glycol are used as the solvent in the described embodiment. At higher temperature, oleyl amine itself acts as a reducing agent and helps in the decomposition of the metal-organic framework.
  • thermally decomposable compounds When the thermally decomposable compounds are added to the solvent, a homogeneous mixture of the catalyst is ensured by conventional dispersion process. This is carried out using, for example, a magnetic bead that confirms homogeneous mixing of the precursors during the entire reaction process.
  • the support includes carbon black, acetylene black, Vulcan XC-72R, synthetic or nano-graphite.
  • suitable support materials are, for example, tin oxide, ⁇ -aluminium oxide, titanium dioxide and silicon dioxide.
  • carbon is particularly preferred as a support material.
  • An advantage of carbon as support material is that it is electrically conducting. When the catalyst is used as an electrocatalyst in a fuel cell, it is necessary for it to be electrically conducting to ensure the proper functioning of the fuel cell. CoPd 2 Se 2 has poor conductivity whereas Pd 17 Se 15 has good electronic conductivity, so the former catalyst is supported by Vulcan XC-72R.
  • CoPd 2 Se 2 may be characterized as having an orthorhombic crystal structure with Ibam space group.
  • Pd 17 Se 15 may be characterized as having a cubic crystal structure with Pm3m space group.
  • CoPchSe2 nanoparticles were synthesized by colloidal synthesis method. 0.2 mmol Pd(acac) 2 , 0.2 mmol H 2 Se0 3 and 0.1 mmol of Co(acac) 2 were mixed in 25 ml oleyl amine in a 50 ml two-necked RB. 800 ⁇ of trioctylphosphine was then added to the solution. The RB was then fitted with a condenser, vacuumed and purged with Ar gas. It was then heated at 220°C for 3 h. The product obtained was repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven at 60°C for 6 h.
  • Pd 17 Se 15 nanoparticles were synthesized by polyol synthesis method.
  • Pd(acac) 2 (0.09 mmol) and H 2 Se0 3 (0.1 mmol) were mixed together in 15 ml TEG in a 50 ml two-necked RB.
  • 40 mg NaBH 4 was then added to the solution followed by stirring thoroughly.
  • the RB was then fitted with a condenser, vacuumed and purged with Ar gas. It was then heated at 220°C for 3 h.
  • the product obtained was repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven at 60°C for 6 h.
  • TEM images and selected area electron diffraction patterns were collected using a JEOL JEM-2010 TEM instrument, and color mapping were done in TECHNAI.
  • the samples for these measurements were prepared by sonicating the nanocrystalline powders in ethanol and drop-casting a small volume onto a carbon-coated copper grid.
  • IPA IPA
  • Nafion solution (5 wt%, Sigma-Aldrich) is diluted with isopropyl alcohol (IPA) to 0.05 wt%.
  • IPA isopropyl alcohol
  • the GC electrode was polished with 0.05 ⁇ alumina slurry and washed several times with distilled water prior to the deposition of catalyst slurry.
  • Commercial Pt/C (10 wt%, Sigma-Aldrich) (with same Pt loading on the electrode) was used for comparison of activity with the as- synthesized catalysts.
  • Oleyl amine is a long chain primary alkyl amine. It can not only act as a solvent and a surfactant but can also serve as an electron donor at elevated temperature. Oleyl amine act as reducing agent at 220 °C and trioctylphosphine (TOP) act as stabilizing agent. TOP also prevents agglomeration of nanoparticles. Adjusting the ratio between them results in intermediate particle size. In our synthesis approach, oleyl amine act as high boiling point coordinating solvent and also as a reducing and a capping agent.
  • the PXRD pattern of CoPd 2 Se 2 and Pd 17 Se 15 nanoparticles were compared with the simulated patterns as shown in Figure 1 (a, b).
  • the prominent peaks (2 ⁇ values) for CoPd 2 Se 2 crystals were observed at 35.94°, 43.6°, 50.36° which corresponds to the (211), (231) and (042) planes of CoPd 2 Se 2 respectively.
  • PdnSei 5 has prominent peaks (20 values) observed at 27.78°, 44.2°, 48.36° corresponding to the (311), (511,333) and (440) planes of the crystal, respectively.
  • the diffraction pattern of PdnSeis could be indexed as cubic with Pm3m space group.
  • the TEM images show that the CoPd 2 Se 2 nanoparticles are less than 100 nm in size.
  • Figure 2 (a, b) clearly shows the presence of nanoparticles having hexagonal morphology.
  • the TEM images in Figure 3 show that the Pd 17 Se 15 nanoparticles are interlinked with each other and have aggregated morphology and the TEM images prove that the nanoparticles are less than 50 nm in size ( Figure 3a, b).
  • d-spacing between two lattice fringes
  • the SAED pattern shown in Figure 3d shows the polycrystalline nature of the nanoparticles.
  • the diffraction pattern contains (310), (400), (510), (810), (742) planes which confirm the formation of the Pdi 7 Sei 5 nanoparticle.
  • j is the measured current density (niAcm " )
  • j k and j d are the kinetic and diffusion limited current densities.
  • Figure 7c shows the corresponding K-L plot obtained from the inverse current densities
  • the Jd term can be termed from the Levich equation:
  • n is the number of electrons transferred
  • F is the Faraday' s constant (96485 C mol “1 )
  • A is the area of the electrode (0.0706 cm “ )
  • D is the diffusion coefficient of 0 2 in 0.1 M
  • Co2 is the concentration of molecular oxygen in 0.1 M KOH solution. (1.2 x 10 " mol L “ ).
  • Durability test was performed for both the catalyst to assess their ability to sustain activity as shown in Figure 8a. Cyclic potential sweeps were performed between 0.4 V and 0.9 V at a scan rate of 0.1 V/s and a rotation speed of 800 rpm in 0 2 saturated 0.1 M KOH. After 50000 cycles, half-wave potential of CoPd 2 Se 2 /V remains high with a slight negative shift of 11 mV in the mixed kinetic-diffusion limited region. However, Pd 17 Se 15 catalyst has a slight positive shift of 13 mV.
  • Tafel plots were plotted to understand the kinetics of the catalysts.
  • tafel slope obtained towards the ORR before cycling was 53.7 mVdec "1 at lower overpotential which decreased to 43 mVdec "1 ( Figure 8b).
  • Tafel slope has a negligible change from 65 mVdec "1 to 67.5 mVdec "1 .
  • This Tafel slope value close to 60 mVdec "1 indicates that the oxygen reduction catalyzed by the catalysts is controlled by the first charge-transfer step, similar to that of a Pt catalyst.
  • methanol tolerance test was performed to check the stability of the catalyst in the case of fuel-crossover in a fuel cell.
  • Linear sweep voltammetry was run in the presence of 1 M methanol keeping all the experimental parameters same (Figure 8c).
  • No significant change in the nature of the curve was observed after the addition of methanol.
  • Tafel slope value also remains unaffected by the addition of methanol ( Figure 8d).
  • a durability test for Pd 17 Se 15 was performed to assess their ability to sustain activity as shown in Figure 9a. Cyclic potential sweeps were performed between 0.4 V and 0.9 V at a scan rate of 0.1 V/s and a rotation speed of 800 rpm in 0 2 saturated 0.1 M KOH. After 50000 cycles, half-wave potential of Pd 17 Se 15 remains high with a slight positive shift of 13 mV in the mixed kinetic-diffusion limited region.
  • a negative shift in the polarization curve can be seen from Figure 9c. It can be due to the electrochemical leaching of selenium out of Pd 17 Se 15 leading to the formation of exposed Pd. This leads to the creation of similar active site i.e. Pd (0) state. Due to the presence of two dissimilar type of Pd i.e. Pd (0) and Pd 17 Se 15 , it leads to the formation of two types of Pd-0 reduction region. Hence, a hump in the Pd-0 reduction region can be seen.
  • Tafel plots were plotted to understand the kinetics of the catalyst as shown in Figure 9d.
  • Tafel slope obtained towards the ORR before cycling was 65 mVdec "1 at lower overpotential which increased to 67.5 mVdec "1 .
  • This Tafel slope value indicates that the oxygen reduction catalyzed by the Pd 17 Se 15 chalcogenide is controlled by the first charge- transfer step, similar to that of a Pt catalyst.
  • the density of state at Fermi level for cobalt could be changed by some electrons transfer from cobalt to selenium, and the density of state would play a significant role in the chemical adsorption process of oxygen. Therefore, the catalytic activity of the Co-Se compounds for the ORR might attribute to the electronic structure modified by selenium.
  • Palladium binds oxygen strongly to its surface. This inhibits the easy desorption of oxygen or oxygen intermediates from the surface. However, the presence of selenium weakens this oxygen binding to the surface. Selenium gains partial negative charge as seen from the XPS data. This repels the oxygen based intermediates from the surface.
  • Figure 10 a, b compares the polarisation curve of the present invention with the state-of-art- material Pd/C. Comparison between the present invention with Pd/C 40 wt% is given in Table 1 as defined below. Onset potential and half- wave potential of the present invention is comparable to that of Pd/C. Tafel plots were plotted to understand the kinetics of the catalyst. Tafel slope obtained towards the ORR was comparable to that of Pd/C showing similar mechanism being followed by the present invention.
  • the present invention can be extended to many other noble metal chalcogenides presented in Table 2 as defined below:

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Abstract

The present invention relates to a catalyst for a polymer electrolyte fuel cell comprising a metal-based chalcogenide comprising a transition metal and/or a noble metal and a chalcogen. The present invention also provides a one-pot method for synthesizing metal-based chalcogenide nanoparticle comprising: (i) mixing one or more metal acetylacetonate or acetate based precursor with a chalcogen precursor in a solvent to obtain a reaction solution; (ii) adding a reagent to the reaction solution; (iii) heating the reaction solution of step (ii) to obtain a reaction product; and (iv) washing the reaction product and drying to obtain a metal-based chalcogenide nanoparticle. The present invention relates to a synthesis of highly stable and durable nanomaterials with selenium rich surface. The catalyst outperforms the present state-of-the-art material Pt/C and Pd/C in terms of stability and durability.

Description

PALLADIUM BASED SELENIDES AS HIGHLY STABLE AND DURABLE CATHODE MATERIALS IN FUEL CELL FOR GREEN ENERGY PRODUCTION FIELD OF THE INVENTION
The present invention relates to synthesis of palladium-based chalcogenides. These materials exhibit high stability and have good activity towards oxygen activation and reduction, because of which they are expected to have their application as cathode materials in fuel cell. More particularly, the present invention relates to a method to synthesize palladium based binary and ternary nanomaterials, CoPd2Se2 and Pd17Se15, and its application as electrocatalyst in the fuel cell. The present invention relates to a synthesis of highly stable and durable nanomaterials with selenium rich surface. The catalyst outperforms the present state-of-the-art material Pt/C and Pd/C in terms of stability and durability. The present disclosure further relates to a unique, one-pot method to synthesize binary and ternary chalcogenides and applications of said nanomaterial as a cathodic electrode material.
BACKGROUND OF THE INVENTION
Fuel cells are receiving growing attention as a viable energy alternative. In general, fuel cells are used to convert chemical energy stored into electrical energy with the production of environmental-friendly by-product in an efficient manner, typically via fuel oxidation and an accompanying oxygen reduction reaction (ORR). Fuel cells are potential energy sources for everything ranging from small electronics to cars and homes. There are different types of fuel cells in existence today, each with varying chemistry, requirements, and uses.
A fuel cell comprises of a fuel electrode (anode), an oxidant electrode (cathode) and an electrolyte. During operation, fuel is continuously fed to the anode where it gets oxidized, and oxygen is reduced at the cathode. However, fuel cell and energy storage devices lack efficient and stable catalysts for such reactions for a long run. To invent commercially efficient fuel cell, designing of a stable catalyst with good activity is a must. In addition, prior arts in literature demonstrated comparatively low stability towards ORR.
A stable, highly active oxygen reduction reaction (ORR) catalyst is a potential candidate in developing fuel cell vehicles. For many decades, it is known that carbon- supported platinum (Pt) based particles can be used as an oxygen reduction catalyst and is commercially available. However, Pt-based ORR catalysts often have issues with stability during operations at a wide range of operating voltages and harsh electrolytic conditions that the catalyst is subjected to. These voltage ranges can stress both the Pt catalyst and the carbon substrate. Methods to improve the durability of the ORR catalyst and to enhance the reaction activity have been the focus of worldwide research for the past several decades.
There remains a continuing need for more durable and stable catalysts for a fuel cell electrode, and especially one that can be readily synthesized. The present invention addresses these and other needs.
The catalyst of the invention is capable of catalyzing the reduction of oxygen. The reduction of oxygen may be achieved by exposing the catalyst to the oxygen. The oxygen may be in any suitable form, such as pure oxygen gas or preferably as an oxygen-containing gas mixture, most preferably air (which may include dry or partially dried or treated air).
ORR which takes place at the cathode of a fuel cell can proceed via four or two electron process. The four electron process involves the combination of oxygen with electrons and protons in a single step to produce water. The two electron process consists of two steps; the first of these produces hydrogen peroxide ions as an intermediate and the second converts these to water. In this invention, it has been confirmed using koutecky- levich plot that the progress of the reaction is taking place through four-electron pathway.
The main issue with the development of highly active and durable electrocatalyst is the use of earth-scarce and highly expensive Pt metal. All the commercially available fuel cell devices are based on Pt catalyst. Though Pt-based electrocatalysts possess considerable activity but their stability is very less. Even, in terms of activity also Pt-based catalysts are not up to the mark. Therefore, development of low-cost Pt-free highly stable and durable electrocatalysts is essential.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a catalyst for a polymer electrolyte fuel cell comprising a metal-based chalcogenide comprising a transition metal and/or a noble metal and a chalcogen.
In an embodiment of the present invention, the metal-based chalcogenide is selected from the group comprising of CoPd2Se2, Pd17Se15, FePd2Se2, CoPd2Te2 and compounds listed in Table 2.
In another embodiment of the present invention, the catalyst is supported on a support material containing carbon.
In yet another embodiment of the present invention, the support material is selected from carbon black, acetylene black, Vulcan XC-72, activated charcoal, synthetic graphite or natural graphite. In yet another embodiment of the present invention, the catalyst is a promising cathode material in a polymer electrolyte membrane fuel cell.
In yet another embodiment of the present invention, the catalyst enhances the four- electron reduction process of oxygen.
In yet another embodiment of the present invention, the catalyst has an onset potential and half-wave potential closer to the state-of-the-art material Pd/C.
In yet another embodiment of the present invention, the catalyst is tolerant towards methanol oxidation.
In yet another embodiment of the present invention, the catalyst shows similar tafel slope as Pd/C that is 60 mVdec"1.
In yet another embodiment of the present invention, the catalyst is used as a cathode material in a polymer electrolyte membrane fuel cell.
In yet another embodiment of the present invention, the electrolyte used in the fuel cell is oxygen-saturated KOH solution.
The present invention also provides a polymer electrolyte membrane fuel cell comprising the catalyst as a cathode material, and the electrolyte used in the fuel cell is oxygen- saturated KOH solution.
The present invention also provides a one-pot method for synthesizing metal-based chalcogenide nanoparticle comprising:
(i) mixing one or more metal acetylacetonate (0.1-0.6 atomic percent) or acetate (0.1-0.6 atomic percent) based precursor with a chalcogen precursor (0.1-0.7 atomic percent) in a solvent (20-50 ml) to obtain a reaction solution;
(ii) adding a reagent (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of 1:3 (v/v) of hexane and ethanol and drying at 60-100°C for 6-12 hrs to obtain a metal-based chalcogenide nanoparticle.
According to the process of the present invention the metal acetylacetonate or acetate based precursor is selected from a group comprising of platinum acetylacetonate (Pt(acac)2), platinum acetate (Pt(OAc)2), palladium acetylacetonate (Pd(acac)2), palladium acetate (Pd(OAc)2), cobalt acetylacetonate (Co(acac)2), cobalt acetate (Co(OAc)2), iron acetylacetonate (Fe(acac)3), iron acetate (Fe(OAc)3), nickel acetylactonate (Ni(acac)2), nickel acetate (Ni(OAc)2), copper acetylactonate (Cu(acac)2), copper acetate (Cu(OAc)2), manganese acetylacetonate (Mn(acac)2) and manganese acetate (Mn(OAc)2.
In an embodiment of the present invention, the chalcogen precursor is selected from a group comprising of selenium powder (Se), seleneous acid (H2Se03), sodium selenide (Na2Se), sodium telluride (Na2Te), sodium sulphide (Na2S), thiourea (NH2CSNH2) and sodium selenosulphate (Na203SSe).
In yet another embodiment of the present invention, the solvent for the synthesis is selected from a group comprising of octyl amine, oleyl amine, ethylene diamine, ethylene glycol and tetraethylene glycol.
In yet another embodiment of the present invention, the reagent is selected from a group comprising of trioctylphosphine, sodium borohydride (NaBH4) and lithium triethylborohydride (Li(C2H5)3BH).
In yet another embodiment of the present invention, the metal-based chalcogenide is selected from the group comprising of CoPd2Se2, Pd17Se15, FePd2Se2, CoPd2Te2 and compounds listed in Table 2.
In yet another embodiment of the present invention, the metal-based chalcogenide nanoparticle is having hexagonal or spherical morphology.
In yet another embodiment of the present invention, the metal-based chalcogenide nanoparticle has a stability of 50000 cycles towards ORR with less than 20 mV shift in half- wave potential.
According to the process of the present invention the metal-based chalcogenide is CoPd2Se2 nanoparticle and obtained by the process comprising:
(i) mixing palladium acetylacetonate (Pd(acac)2) (0.1-0.6 atomic percent), and cobalt acetylacetonate (Co(acac)2) (0.1-0.6 atomic percent),with a seleneous acid (H2Se03) (0.1-0.7 atomic percent), in a oleyl amine (20-50 ml) to obtain a reaction solution;
(ii) adding a trioctylphosphine (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of hexane and ethanol and drying at 60-120°C for 6-12 hrs to obtain a CoPd2Se2 nanoparticle.
According to the process of the present invention the metal-based chalcogenide is PdnSeis nanoparticle and obtained by the process comprising: (i) mixing palladium acetylacetonate( Pd(acac)2) (0.1-0.6 atomic percent) with a seleneous acid (H2Se03) (0.-0.7 atomic percent), in a tetraethylene glycol (20-50 ml) to obtain a reaction solution;
(ii) adding a sodium borohydride (NaBH4) (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of hexane and ethanol and drying at 60-120°C for 6-12 hrs to obtain a Pd17Se15 nanoparticles.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The reference will now be made to exemplary embodiments so that the disclosure may be readily understood and put into practical effect. It will be illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to illustrate the embodiments further and explain various principles and advantages, in accordance with the present disclosure wherein:
Figure 1 (a) is a X-ray diffraction pattern (XRD) of ternary chalcogenide CoPd2Se2. It shows the intensity of the diffraction peak in arbitrary unit versus the angle of diffraction. Major diffraction peaks at 34.16 °, 35.94 °, 39.90 °, 43.66 °, 50.36° and 52.26° correspond to (220), (211), (112), (231), (042) and (060) planes respectively. It corresponds to orthorhombic crystal system with Ibam space group, (b) is a PXRD pattern of binary chalcogenide PdnSe^. It has prominent peaks (2Θ values) observed at 27.78°, 44.2°, 48.36° corresponding to the (311), (511,333) and (440) planes of the crystal, respectively. The diffraction pattern of Pdi7Sei5 could be indexed as cubic with Pm3m space group. Figure 2 shows (a,b) TEM images of as -synthesized CoPd2Se2 nanoparticles confirming its hexagonal morphology, (c) High-Resolution Transmission Electron Microscopy (HRTEM) images indicating the exposed crystallographic facets, (d) Selected Area Electron Diffraction (SAED) pattern shows the polycrystalline nature of CoPd2Se2 nanoparticles. Figure 3 shows (a,b) TEM images of as-synthesized PdnSe^ nanoparticles showing the aggregated nature of the particles, (c) High-Resolution Transmission Electron Microscopy (HRTEM) images indicating the exposed crystallographic facets, (d) Selected Area Electron Diffraction (SAED) pattern shows the polycrystalline nature of PdnSe^ nanoparticles. Figure 4 shows (a) the FESEM images of CoPd2Se2 nanoparticles. Hexagonal morphology of the nanoparticles can be clearly seen from the images, (b) EDX spectrum of CoPd2Se2 nanoparticles. The inset table represents the composition of individual elements present in the system.
Figure 5 shows (a) SEM images of the as-prepared Pd17Se15, (b) elemental mapping of Pd17Se15 indicates the presence of both the elements. Elemental mapping of individual elements - (c) Se (pink) and (d) Pd (purple), (e) EDX spectrum of Pd17Se15 nanoparticles. The elemental composition of the sample is provided as an inset.
Figure 6 shows (i) core level XPS spectra of (a) Co, (b) Pd and (c) Se elements in CoPd2Se2 nanocomposite and (ii) core level XPS spectra of Pd17Se15 nanoparticles. High resolution XPS spectrum of (a) Pd-3<¾/2, Pd-3<¾/2 and (b) Se-3<i.
Figure 7 shows (a) LS V polarization curve at different rpm rate in 0.1 M KOH at a sweep rate of 5 mV/sec, (b) the koutecky-levich plot for CoPd2Se2/Vulcan nanocomposite at different potentials. The plots are generated from the LSV curves of all the samples tested in oxygen- saturated 0.1 M KOH solution with different rotating speeds, (c) Tafel plot (overpotential plotted vs. logarithm of current density) indicating faster reduction kinetics on hexagonal shaped nanoparticles, and (d) no. of electrons involved in ORR as a function of potential applied.
Figure 8 shows (a) LSV polarization curve before and after 50000 cycles in 0.1 M KOH at a sweep rate of 5 mV/sec, (b) Tafel slope comparison before and after ADT showing slight decrease in the Tafel slope value, (c) polarization curve in the presence of 1 M methanol showing almost no effect on the catalyst, and (d) Tafel slope of catalyst in absence and presence of 1 M methanol.
Figure 9 shows (a) Polarization curve of Pd17Se15 before and after cycling, (b) CV curve as a function of cycle number showing the removal of Se from the surface due to prolonged cycling, (c) ORR polarization curve showing the negative shift due to exposed Pd sites and (d) tafel slope showing that the same mechanism is being followed before and after cycling. Figure 10 shows (a) the comparison of the present invention with the state-of-the-art material Pd/C and (b) tafel slope of the present invention is similar to that of the state-of- the-art material showing that the present invention follows similar mechanism as that of the Pd/C.
Table 1 shows the comparison of the present invention with the state-of-the-art catalyst Pd/C 40 wt%. Table 2 shows that the present invention is not limited to the referred examples but can be extended to the following list of materials.
DETAILED DESCRIPTION OF THE INVENTION
While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.
The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.
The present invention addresses the issues of problem/drawbacks of the existing processes with the development of low-cost chalcogenide materials with earth abundant and less expensive elements. Moreover, catalysts of the present invention are stable for 50000 electrochemical cycles, highest reported so far for any ORR catalyst. In addition, catalysts of the present invention show activity as good as commercial Pd/C but durability is far better than Pd/C. Unlike many complicated synthesis methods, the present invention provides a facile one-pot synthesis method to synthesize the named catalysts.
This invention will be useful in the fabrication of highly efficient and robust fuel cell, which is a renewable and green source of energy. Two major problems what the whole world is facing today: depletion of fossil fuel leading to the energy crisis and global warming due to the high rate of C02 emission to the atmosphere. Both the issues need to be addressed in no time. Therefore, use of fuel cell as a source of will solve the above- mentioned issue. Already in different countries all over the world, fuel cell is being used as a green source of energy not only in portable devices but also in other stationary systems. The major challenge in the development of the highly efficient fuel cell is the development of highly active and stable electrocatalysts. At the current state, the active catalysts are made of expensive and earth scarce Pt metal with very low stability. Not only stability issue but also the activity of the compounds is not up to the mark. This limits its use in large-scale. This invention mainly discusses about the design and development of highly active and robust Pt-free low-cost electrocatalysts, which are superior to commercial Pt catalysts in terms of stability and durability. This finding will not only solve the stability issue of fuel cell but also will make the availability of the fuel cell more convenient.
Embodiments of the present invention provide a one-pot method to synthesize palladium based binary and ternary chalcogenides for oxygen reduction reaction that offers comparable activity while maintaining exceptional durability and long-term stability. The activity and durability properties of the disclosed ORR catalysts may be due to the preparation methods used and crystal structure of the compound.
In an embodiment of the present invention CoPd2Se2 nanoparticles are synthesized by colloidal synthesis method. Pd(acac)2, H2Se03 and Co(acac)2 are mixed in oleyl amine in a two-necked RB. Trioctylphosphine is then added to the solution. The RB is then fitted with a condenser, vacuumed and purged with Ar gas. It is then heated for a few hours. The product obtained is repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven. In preferred embodiments, the amount of trioctylphosphine (stabilizing agent) used is 600-1000 μΐ. The heating is preferably done at 220 °C-250 °C for 2-6 h. The drying is preferably done at 60°C for 6-12 h.
In another embodiment of the present invention, Pd17Se15 nanoparticles are synthesized by polyol synthesis method. Pd(acac)2 (0.09-0.12 mmol) and H2Se03 (0.1 mmol) are mixed together in TEG (15 ml) in a two-necked RB (50 ml). NaBH4 (40 mg), which is used as a reducing agent, is then added to the solution followed by stirring thoroughly. The RB is then fitted with a condenser, vacuumed and purged with Ar gas. It is then heated (220-250°C for 3-6 h). The product obtained is repeatedly washed with hexane- ethanol mixture for several times and then dried in vacuum oven (60°C for 6-12 h).
Electrocatalytic evaluation of the prepared catalyst was done using a rotating disc electrode technique on samples both before and after extended use as a catalyst in ORR. Prolonged use here was accomplished by subjecting the catalyst to cyclic voltammetry, which involved cycling 50000 times repeatedly for about one week.
The described invention meets the present-day demand of a durable cathode catalyst with good activity for a fuel cell. Methods of preparing the catalyst are also described. It consists of a transition metal and/or a noble metal, and a chalcogenide non-metal.
Preferably, the transition metal is chosen from the group consisting of nickel, cobalt and iron. Particularly, transition metal used in one of the embodiment is cobalt.
Preferably, the noble metal is selected from the group consisting of palladium and platinum. Particularly, noble metal used in one of the embodiment is palladium. The chalcogen is preferably selected from a group consisting of sulphur, selenium and tellurium. Particularly, chalcogen used in of the embodiment is selenium.
As used herein, the term "noble metal" refers to the metals of second and third triads of group VIII of the periodic table namely ruthenium, rhodium, palladium, platinum, osmium and iridium. "Chalcogenide" refers to the elements of group 16 family in the periodic table with electronegative character.
In one of the preferred embodiment, the present invention discloses a cathode catalyst for a polymer electrolyte fuel cell comprising a transition metal and/or a noble metal and a chalcogen.
In one embodiment the cathode catalyst for polymer electrolyte membrane fuel cell, wherein said alloy catalyst is supported on a support material containing carbon. The catalyst is supported by carbon black, acetylene black, Vulcan XC-72R, activated charcoal, synthetic graphite or natural graphite.
In one of the preferred embodiment present invention provides a method for making a cathode catalyst for a polymer electrolyte fuel cell comprising a transition metal and/or a noble metal and a chalcogen wherein said method comprises one-pot synthesis method.
The synthesis method includes heating at a temperature range of 220°C-250°C. The morphology of the nanoparticles/ cathode catalyst obtained by this method can be hexagonal/spherical. The cathode catalyst obtained by this method is active towards ORR. The electrolyte used is oxygen- saturated KOH solution.
In another embodiment, the cathode catalyst of the present invention has a stability of 50000 cycles towards ORR with less than 20 mV shift in half-wave potential. The catalyst enhances the four-electron reduction process of oxygen. The catalyst has an onset potential and half-wave potential closer to the state-of-the-art material Pd/C. The catalyst is tolerant towards methanol oxidation. The catalyst shows similar tafel slope as Pd/C i.e. 60 mVdec"1. The catalyst can be used as a cathode material in a fuel cell.
In a preferred embodiment, as two examples, the ternary chalcogenide has a molar ratio of transition metal: noble metal: chalcogen as 1:2:2 and the binary chalcogenide has a compositional ratio of noble metal: chalcogenide as 17: 15.
For the synthesis, the precursor of the transition and the noble metals are preferably present as a metal-organic complex. Preferred ligands are acetylacetonate or acetate. Selenium is preferably present as seleneous acid. Decomposition of the metal organic complex precursors requires high temperature and reductive environment, which is ensured by the use of reducing solvent at high temperature. The preferred solvent for the synthesis includes oleyl amine, ethylene diamine and tetraethylene glycol. Particularly, oleyl amine and tetraethylene glycol are used as the solvent in the described embodiment. At higher temperature, oleyl amine itself acts as a reducing agent and helps in the decomposition of the metal-organic framework.
When the thermally decomposable compounds are added to the solvent, a homogeneous mixture of the catalyst is ensured by conventional dispersion process. This is carried out using, for example, a magnetic bead that confirms homogeneous mixing of the precursors during the entire reaction process.
When the catalyst is applied to a support, a large specific area can be obtained which increases the current density of the catalyst.
The support includes carbon black, acetylene black, Vulcan XC-72R, synthetic or nano-graphite. Further, suitable support materials are, for example, tin oxide, γ-aluminium oxide, titanium dioxide and silicon dioxide. However, carbon is particularly preferred as a support material. An advantage of carbon as support material is that it is electrically conducting. When the catalyst is used as an electrocatalyst in a fuel cell, it is necessary for it to be electrically conducting to ensure the proper functioning of the fuel cell. CoPd2Se2 has poor conductivity whereas Pd17Se15 has good electronic conductivity, so the former catalyst is supported by Vulcan XC-72R.
This disclosure relates to the synthesis of ternary chalcogenide CoPd2Se2 as a model compound in chalcogenide based systems, which demonstrates unusually high durability towards ORR. In one of the embodiment, CoPd2Se2 may be characterized as having an orthorhombic crystal structure with Ibam space group.
In one of the embodiment, Pd17Se15 may be characterized as having a cubic crystal structure with Pm3m space group.
The following examples illustrate the various features and advantages of the invention and are not intended to limit the invention thereto. While the examples refer to the fabrication of a cathode catalyst, this material represents a preferred embodiment of the invention, and other metals and chalcogens described herein may also be used.
EXAMPLES
Experimental details
Materials- Palladium acetylacetonate (Pd(C5H702)2, 99%), cobalt acetylacetonate (Co(C5H702)2, 99%), selenous acid (H2Se03, 98%), trioctylphosphine (P(C8Hi7)3, 90%), oleylamine (Ci8H35NH2, 70%) were purchased from Sigma-Aldrich. All the reagents were used without further purification. Milli-Q water (18.2 MQcm) was used throughout the synthesis and electrochemical measurements.
Example 1
Synthesis of CoPchSe2 nanoparticles: CoPd^Se? nanoparticles were synthesized by colloidal synthesis method. 0.2 mmol Pd(acac)2, 0.2 mmol H2Se03 and 0.1 mmol of Co(acac)2 were mixed in 25 ml oleyl amine in a 50 ml two-necked RB. 800 μΐ of trioctylphosphine was then added to the solution. The RB was then fitted with a condenser, vacuumed and purged with Ar gas. It was then heated at 220°C for 3 h. The product obtained was repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven at 60°C for 6 h.
Example 2
Synthesis of Pdi7Seij nanoparticles: Pd17Se15 nanoparticles were synthesized by polyol synthesis method. Pd(acac)2 (0.09 mmol) and H2Se03 (0.1 mmol) were mixed together in 15 ml TEG in a 50 ml two-necked RB. 40 mg NaBH4 was then added to the solution followed by stirring thoroughly. The RB was then fitted with a condenser, vacuumed and purged with Ar gas. It was then heated at 220°C for 3 h. The product obtained was repeatedly washed with the hexane-ethanol mixture for several times and then dried in vacuum oven at 60°C for 6 h.
Example 3
Characterization: The PXRD measurements at room temperature were carried out on a Rigaku miniflex X-ray diffractometer with Cu-Ka as the X-ray source (λ = 1.5406 A). The instrument is equipped with a position sensitive detector in the angular range 20° < 2Θ < 90° with the step size 0.02° and a scan rate of 1 sec/step calibrated against corundum standard. The experimental patterns were compared to the pattern simulated from the database. (Figure 1)
Quantitative microanalysis on all the samples was performed with a FEI NOVA NANOSEM 600 instrument equipped with an ED AX® instrument. Data were acquired with an accelerating voltage of 20 kV and a 100 s accumulation time. The EDAX analysis was performed using P/B-ZAF standardless method (where, Z = atomic no. correction factor, A = absorption correction factor, F = fluorescence factor, P/B = peak to background model) on selected spots and points. (Figure 4b)
TEM images and selected area electron diffraction patterns were collected using a JEOL JEM-2010 TEM instrument, and color mapping were done in TECHNAI. The samples for these measurements were prepared by sonicating the nanocrystalline powders in ethanol and drop-casting a small volume onto a carbon-coated copper grid.
XPS measurement was performed on an Omicron Nanotechnology spectrometer using a Mg-Jca (λ = 1253.6 eV) X-ray source with a relative composition detection better than 0.1%.
Example 4
Procedure for electrochemical measurements: In the previous embodiment, catalyst compositions were synthesized chemically and electrochemically tested for performance. All the electrochemical measurements were carried out using a CHI 760E electrochemical workstation with three electrode channels at room temperature. A conventional three- electrode set-up consisting of a glassy carbon (GC) (having diameter 3 mm) as working electrode, a platinum wire as a counter electrode and Hg/HgO (MMO) as a reference electrode were used. Before all the measurements, the electrolyte was de-aerated with the continuous purging of nitrogen gas for 30 min. The catalyst ink was prepared by dispersing 1 mg of catalyst in 200 [iL of a mixed solvent solution (IPA: H20=l :3 v/v). Nafion solution (5 wt%, Sigma-Aldrich) is diluted with isopropyl alcohol (IPA) to 0.05 wt%. From the prepared catalyst ink, a 5 μΐ^ of the slurry was drop-casted on GC electrode, and then one drop of 0.05 wt% of Nafion solution have been added to the drop-casted electrode and dried overnight in air. The GC electrode was polished with 0.05 μπι alumina slurry and washed several times with distilled water prior to the deposition of catalyst slurry. Commercial Pt/C (10 wt%, Sigma-Aldrich) (with same Pt loading on the electrode) was used for comparison of activity with the as- synthesized catalysts. Chronoamperometric (CA) measurements were performed in 02 saturated 0.1 M KOH electrolyte solution. Linear sweep voltammetry (LSV) was recorded at a sweep rate of 5 mV/s in 0.1 M KOH electrolyte solution under steady state conditions. Tafel plots (TP) were derived from LSV measurement.
Oleyl amine is a long chain primary alkyl amine. It can not only act as a solvent and a surfactant but can also serve as an electron donor at elevated temperature. Oleyl amine act as reducing agent at 220 °C and trioctylphosphine (TOP) act as stabilizing agent. TOP also prevents agglomeration of nanoparticles. Adjusting the ratio between them results in intermediate particle size. In our synthesis approach, oleyl amine act as high boiling point coordinating solvent and also as a reducing and a capping agent.
The PXRD pattern of CoPd2Se2 and Pd17Se15 nanoparticles were compared with the simulated patterns as shown in Figure 1 (a, b). The prominent peaks (2Θ values) for CoPd2Se2 crystals were observed at 35.94°, 43.6°, 50.36° which corresponds to the (211), (231) and (042) planes of CoPd2Se2 respectively. The diffraction pattern could be indexed as orthorhombic with Ibam space group and lattice parameters a =5.993 A, b =10.493 A, c =5.003 A. PdnSei5 has prominent peaks (20 values) observed at 27.78°, 44.2°, 48.36° corresponding to the (311), (511,333) and (440) planes of the crystal, respectively. The diffraction pattern of PdnSeis could be indexed as cubic with Pm3m space group.
The TEM images show that the CoPd2Se2 nanoparticles are less than 100 nm in size. Figure 2 (a, b) clearly shows the presence of nanoparticles having hexagonal morphology. The TEM images in Figure 3 show that the Pd17Se15 nanoparticles are interlinked with each other and have aggregated morphology and the TEM images prove that the nanoparticles are less than 50 nm in size (Figure 3a, b). From HRTEM image, d-spacing (between two lattice fringes) was calculated to be 0.47 nm and 0.327 nm which corresponds to the (210) and (311) planes of the particles are exposed (Figure 3c). The SAED pattern shown in Figure 3d shows the polycrystalline nature of the nanoparticles. The diffraction pattern contains (310), (400), (510), (810), (742) planes which confirm the formation of the Pdi7Sei5 nanoparticle.
The FESEM images corroborate with the TEM images and indicate that the CoPd2Se2 nanoparticles have hexagonal-like morphology (Figure 4a). The EDX spectra (Figure 4b) from the FESEM analysis clearly confirms the presence of Co, Pd, and Se in the sample. In the ED AX spectrum, peaks are observed at 0.7 and 6.9 keV for Co, 0.25 and 2.8 keV for Pd and 1.3 and 11.25 keV for Se. The Strong peak at 1.7 keV confirms the presence of Si element from the silicon wafer on which the sample has been coated. The absence of other elements indicates that the prepared nanoparticles have a high purity level. Similar observation is made in the case of Pd17Se15 except for the Co peak (Figure 5a, b).
XPS was employed to understand the elemental composition of the sample. From
Figure 6 (i, ii), it is clear that Co 2/?3/2 located at 780.2 eV corresponds to +2 oxidation state, Pd-3<¾/2 and Pd-3<¾/2 are located at 336.3 eV and 341.5 eV, respectively. The location of the peak 3<¾/2 corresponds to +2 oxidation state of Pd. Se-3<¾/2 is located at 54.7 eV corresponds to -2 oxidation state of Se. Integration of the area under the peak and dividing by the relative sensitivity factor (RSF) discloses that the surface has a Pd:Se ratio of 1:2 in PdnSeis.
Keeping all the parameters same, RDE measurement is carried out on the catalyst modified GC electrode in N2 saturated, and 02 saturated 0.1 M KOH (Figure 7a). In the voltammetric profile, Pd-0 reduction (-0.25 to -0.4V) region is well defined. The polarization curves for ORR on the catalyst surface at different rotation rates are shown in Figure 7b in which current densities are normalized with respect to the geometrical surface area (0.0706 cm ). They all reached a well-defined diffusion limited current.
The current-potential dependence of the reaction rate can be described by Koutecky-
Levich (K-L) equation:
Figure imgf000016_0001
where j is the measured current density (niAcm" ), and jk and jd are the kinetic and diffusion limited current densities.
Figure 7c shows the corresponding K-L plot obtained from the inverse current densities
-1/2
as a function of the inverse square root of rotation rate (co~ ) at different potentials, respectively.
The Jd term can be termed from the Levich equation:
j M n il „CT->2 3 -1/6 1/2^
Jd =— = 0.62 nbD υ ω o2
where n is the number of electrons transferred, F is the Faraday' s constant (96485 C mol"1), A is the area of the electrode (0.0706 cm" ), D is the diffusion coefficient of 02 in 0.1 M
5 2 1 2
KOH solution (1.9 x 10"J em's"1), υ is the kinematic viscosity of the electrolyte (0.01 cm s" l), ω is the angular frequency of rotation, ω= 2π/760, / is the RDE rotation rate in rpm, and
-3 -1
Co2 is the concentration of molecular oxygen in 0.1 M KOH solution. (1.2 x 10" mol L " ).
— 1/2
The plot of 1/j vs. ω for potential range of 0.1-0.6 V (vs. RHE) yields a series of essentially parallel straight lines, having a slope value of B. The linearity and parallelism of all lines in Figure 7d indicates that the electron number transferred per oxygen molecule and the active surface area of the catalyst does not obviously change in the potential range measured. A value of n=4 is obtained for the catalyst CoPd2Se2, unlike Co-Se and CoSe2/C which has a value of n=3.4 and 3.5 respectively.
Example 5
Durability Test and Kinetics study for CoPchSe2 and Pdi7Seis nanoparticles: Durability test was performed for both the catalyst to assess their ability to sustain activity as shown in Figure 8a. Cyclic potential sweeps were performed between 0.4 V and 0.9 V at a scan rate of 0.1 V/s and a rotation speed of 800 rpm in 02 saturated 0.1 M KOH. After 50000 cycles, half-wave potential of CoPd2Se2/V remains high with a slight negative shift of 11 mV in the mixed kinetic-diffusion limited region. However, Pd17Se15 catalyst has a slight positive shift of 13 mV.
Tafel plots were plotted to understand the kinetics of the catalysts. In case of CoPd2Se2, tafel slope obtained towards the ORR before cycling was 53.7 mVdec"1 at lower overpotential which decreased to 43 mVdec"1 (Figure 8b). For Pd17Se15, Tafel slope has a negligible change from 65 mVdec"1 to 67.5 mVdec"1. This Tafel slope value close to 60 mVdec"1 indicates that the oxygen reduction catalyzed by the catalysts is controlled by the first charge-transfer step, similar to that of a Pt catalyst.
In another embodiment, methanol tolerance test was performed to check the stability of the catalyst in the case of fuel-crossover in a fuel cell. Linear sweep voltammetry was run in the presence of 1 M methanol keeping all the experimental parameters same (Figure 8c). However, no significant change in the nature of the curve was observed after the addition of methanol. Tafel slope value also remains unaffected by the addition of methanol (Figure 8d).
A durability test for Pd17Se15 was performed to assess their ability to sustain activity as shown in Figure 9a. Cyclic potential sweeps were performed between 0.4 V and 0.9 V at a scan rate of 0.1 V/s and a rotation speed of 800 rpm in 02 saturated 0.1 M KOH. After 50000 cycles, half-wave potential of Pd17Se15 remains high with a slight positive shift of 13 mV in the mixed kinetic-diffusion limited region.
2- 2- Selenium on the surface exists as selenite and selenate ions (Se03 and Se04 ) in alkaline medium at higher potential according to Pourbaix diagram for selenium. Selenate and selenite ions are highly soluble in aqueous medium and hence it was oxidatively removed during prolonged cycling at the higher potential range. This can be seen from the reduction of oxidative current at a higher potential which corresponds to selenium oxidation as well as Pd oxidation. Due to the prolonged cycling process, Se on the surface gets oxidized to form Se03 2-" and Se042-". This Se042-" being highly soluble in aqueous medium gets oxidatively removed from the surface exposing palladium active sites. Elemental Pd being active for ORR further shifts the polarization curve towards the positive potential. Exposed Pd active sites can be seen in Figure 9b which clearly shows the Hupd region, characteristic of Pd.
A negative shift in the polarization curve can be seen from Figure 9c. It can be due to the electrochemical leaching of selenium out of Pd17Se15 leading to the formation of exposed Pd. This leads to the creation of similar active site i.e. Pd (0) state. Due to the presence of two dissimilar type of Pd i.e. Pd (0) and Pd17Se15, it leads to the formation of two types of Pd-0 reduction region. Hence, a hump in the Pd-0 reduction region can be seen.
Tafel plots were plotted to understand the kinetics of the catalyst as shown in Figure 9d. Tafel slope obtained towards the ORR before cycling was 65 mVdec"1 at lower overpotential which increased to 67.5 mVdec"1. This Tafel slope value indicates that the oxygen reduction catalyzed by the Pd17Se15 chalcogenide is controlled by the first charge- transfer step, similar to that of a Pt catalyst.
The density of state at Fermi level for cobalt could be changed by some electrons transfer from cobalt to selenium, and the density of state would play a significant role in the chemical adsorption process of oxygen. Therefore, the catalytic activity of the Co-Se compounds for the ORR might attribute to the electronic structure modified by selenium.
Palladium binds oxygen strongly to its surface. This inhibits the easy desorption of oxygen or oxygen intermediates from the surface. However, the presence of selenium weakens this oxygen binding to the surface. Selenium gains partial negative charge as seen from the XPS data. This repels the oxygen based intermediates from the surface.
Figure 10 a, b compares the polarisation curve of the present invention with the state-of-art- material Pd/C. Comparison between the present invention with Pd/C 40 wt% is given in Table 1 as defined below. Onset potential and half- wave potential of the present invention is comparable to that of Pd/C. Tafel plots were plotted to understand the kinetics of the catalyst. Tafel slope obtained towards the ORR was comparable to that of Pd/C showing similar mechanism being followed by the present invention.
The present invention can be extended to many other noble metal chalcogenides presented in Table 2 as defined below:
Table 1
Figure imgf000019_0001
Table 2.
SI. No. Compound Reference
1. PtSe2 Thomassen et. al., Z. Phys. Chem. (Abt. B) 1929, 2-349
2. PtTe2 Thomassen et. al., Z. Phys. Chem. (Abt. B) 1929, 2-349
3. PdTe2 Thomassen et. al., Z. Phys. Chem. (Abt. B) 1929, 2-349
4. PdTe Thomassen et. al., Z. Phys. Chem. (Abt. B) 1929, 2-349
5. PtS; Thomassen et. al., Z. Phys. Chem. (Abt. B) 1929, 2-349
6. PdS Gaskell et. al., Z. Kristallogr. 1937, 96, 203-213
7. PtTe Meijer et. al., Am. Mineral., 1955, 40, 693-696
8. Pd ;S Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
9. Pd4Se Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
10. Pd,:Se Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
SI. No. Compound Reference
11. PdSe2 Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
12. Pdi6S7 Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
13. PdS; Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
14. Pd17Se15 Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
15. Pd ;Te Gronvolde et. al., Acta Chem. Scand. 1956, 10, 1620-1634
16. PdSe Schubert ef. al., Naturwissenschaften 1957, 44, 229-230
17. PtS Gronvold ef. al., Acta Chem. Scand. 1960, 14, 1879-1893
18. PtTe2 Gronvold ef. al., Acta Chem. Scand. 1960, 14, 1879-1893 19. Pd3Te2 Kim ef. al., J. Less-Common Met. 1990, 162, 61-74
20. Pd3S Rost et. al., Acta Chem. Scand. 1968, 22, 819-826
21. Pt3Te4 Bhan et. al., J. Less-Common Met. 1969, 19, 121-140 22. Pt2Te3 Bhan ef. al., J. Less-Common Met. 1969, 19, 121-140
23. Pd3 5Te Cenzual et. al., Acta Crystallogr. B 1991, 47, 433-439
24. Pd20Te7 Kim et. al., Can. Mineral. 1991, 29, 401-409
25. Pt5Se4 Matkovic et. al., J. Less-Common Met. 1977, 55, 185-190
26. Pd9Te4 Kim ef. al., J. Less-Common Met. 1990, 162, 61-74
27. Pd7Se4 Olsen et. al., Acta Chem. Scand. A 1979, 33, 251-256
28. Pd7Se2 Olsen et. al., Acta Chem. Scand. A 1979, 33, 251-256
29. Pd13Te3 Janetzky et. al., Z. Anorg. Allg. Chem. 2006, 632, 837-844
30. PtSeTe Hulliger et. al., J. Phys. Chem. Solids 1965, 26, 639-645
31. PdSeTe Hulliger et. al., J. Phys. Chem. Solids 1965, 26, 639-645
32. PdSSe Hulliger et. al., J. Phys. Chem. Solids 1965, 26, 639-645
33. PtSSe Hulliger et. al., J. Phys. Chem. Solids 1965, 26, 639-645
34. PtSnTe Schubert et. al., Z. Metallkd. 1971, 62, 667-675
35. MnPdTe i Helmholdt et. al., J. Less-Common Met. 1986, 123, 169-173 j
36. GePtS Schubert et. al., Z. Metallkd. 1971, 62, 667-675
37. PtSeSi Entner et. al., Acta Crystallogr. B 1973, 29, 1557-1560
38. PtGeSe Schubert et. al., Z. Metallkd. 1971, 62, 667-675
39. Co8PdS8 Knop et. al., J. Solid State Chem. 1976, 16, 97-116
40. Cu3Pd13S7 Matkovic ef. al., J. Less-Common Met. 1976, 50, 165-176
41. CePd3S4 Keszler ef. al., J. Chem. Soc. (Dalton Trans.) 1985,2369
42. EuPd3S4 Keszler ef. al., J. Chem. Soc. (Dalton Trans.) 1985,2369
43. PdSe6Ta2 Keszler ef. al., Inorg. Chem. 1985, 24, 3063-3067
44. Nb2PdSes Keszler ef. al., Inorg. Chem. 1985, 24, 3063-3067
45. PdS6Ta2 Keszler ef. al., Inorg. Chem. 1985, 24, 3063-3067
46. Nb2PdS6 Keszler ef. al., Inorg. Chem. 1985, 24, 3063-3067
47. Pd3Se8Ta2 Keszler ef. al., J. Solid State Chem. 1985, 57, 68-81 48. PtSe7Ta2 Sunshine et. al., Inorg. Chem.1986, 25, 4355-4358
49. Pt3Se8Ta2 Squattrito et. al., J. Solid State Chem.1986, 64, 261-269
50. NbPdTe5 Liimatta et al., J. Solid State Chem.1988, 77, 141-147
51. Ta3Pd3Te14 Liimatta et. al., J. Solid State Chem.1989, 78, 7-16
52. Ta4Pd3Te16 Mar et. al., J. Chem. Soc. (Dalton Trans.) 1991, 639
53. Ta2Pd3Te5 Tremel et. al., Angew. Chem.1993, 105, 1795-1798
54. PtSiTe Mansuetto et. al., Z. Kristallogr.1994, 209, 708
55. CuPt2S4 Gross et al., Z. Anorg. Allg. Chem.1994, 620, 1909-1914
56. GePdS3 Johrendt et. al., Chem. Eur. J.1998, 4, 1829-1833
57. Cu2Pd3Se4 Topa et. al., Can. Mineral.2006, 44, 497-505
58. NiPd2Te2 Pocha et. al., J. Solid State Chem.2007, 180, 191-197
59. CoPd2Te2 Pocha et. al., J. Solid State Chem.2007, 180, 191-197
60. FePd2Se2 Pocha et. al., J. Solid State Chem.2007, 180, 191-197
61. CoPd2Se2 Pocha et. al., J. Solid State Chem.2007, 180, 191-197
5

Claims

Claims:
1. A catalyst for a polymer electrolyte fuel cell comprising a metal-based chalcogenide comprising a transition metal and/or a noble metal and a chalcogen.
2. The catalyst as claimed in claim 1, wherein the metal-based chalcogenide is selected from the group comprising of CoPd2Se2, Pd17Se15, FePd2Se2, CoPd2Te2 and compounds listed in Table 2.
3. The catalyst as claimed in claim 1, wherein the catalyst is supported on a support material containing carbon.
4. The catalyst as claimed in claim 3, wherein the support material is selected from carbon black, acetylene black, Vulcan XC-72, activated charcoal, synthetic graphite or natural graphite.
5. The catalyst as claimed in claim 1, wherein the catalyst is a promising cathode material in a polymer electrolyte membrane fuel cell.
6. The catalyst as claimed in claim 1, wherein the catalyst enhances the four- electron reduction process of oxygen.
7. The catalyst as claimed in claim 1, wherein the catalyst has an onset potential and half-wave potential closer to the state-of-the-art material Pd/C.
8. The catalyst as claimed in claim 1, wherein the catalyst is tolerant towards methanol oxidation.
9. The catalyst as claimed in claim 1, wherein the catalyst shows similar tafel slope as Pd/C that is 60 mVdec"1.
10. The catalyst as claimed in claim 1, wherein the electrolyte used in the fuel cell is oxygen-saturated KOH solution.
11. A one-pot method for synthesizing metal-based chalcogenide nanoparticle comprising:
(i) mixing one or more metal acetylacetonate (0.1-0.6 atomic percent) or acetate (0.1-0.6 atomic percent) based precursor with a chalcogen precursor (0.1-0.7 atomic percent) in a solvent (20-50 ml) to obtain a reaction solution;
(ii) adding a reagent (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250'3C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of 1:3 (v/v) of hexane and ethanol and drying at 60-100°C for 6-12 hrs to obtain a metal-based chalcogenide nanoparticle.
12. The process as claimed in claim 11, wherein the metal acetylacetonate or acetate based precursor is selected from a group comprising of platinum acetylacetonate (Pt(acac)2), platinum acetate (Pt(OAc)2), palladium acetylacetonate (Pd(acac)2), palladium acetate (Pd(OAc)2), cobalt acetylacetonate (Co(acac)2), cobalt acetate (Co(OAc)2), iron acetylacetonate (Fe(acac)3), iron acetate (Fe(OAc)3), nickel acetylactonate (Ni(acac)2), nickel acetate (Ni(OAc)2), copper acetylactonate (Cu(acac)2), copper acetate (Cu(OAc)2), manganese acetylacetonate (Mn(acac)2) and manganese acetate (Mn(OAc)2.
13. The process as claimed in claim 11, wherein the chalcogen precursor is selected from a group comprising of selenium powder (Se), seleneous acid (H2Se03), sodium selenide (Na2Se), sodium telluride (Na2Te), sodium sulphide (Na2S), thiourea (NH2CSNH2) and sodium selenosulphate (Na20 SSe).
14. The process as claimed in claim 11, wherein the solvent for the synthesis is selected from a group comprising of octyl amine, oleyl amine, ethylene diamine, ethylene glycol and tetraethylene glycol.
15. The process as claimed in claim 11, wherein the reagent is selected from a group comprising of trioctylphosphine, sodium borohydride (NaBH4) and lithium triethylborohydride (Li(C2H5) BH).
16. The process as claimed in claim 11, wherein the metal -based chalcogenide nanoparticle is having hexagonal or spherical morphology.
17. The process as claimed in claim 11, wherein the metal-based chalcogenide nanoparticle has a stability of 50000 cycles towards ORR with less than 20 mV shift in half- wave potential.
18. The process as claimed in claim 11, wherein the metal-based chalcogenide is CoPd2Se2 nanoparticle and obtained by the process comprising:
(i) mixing palladium acetylacetonate (Pd(acac)2) (0.1-0.6 atomic percent), and cobalt acetylacetonate (Co(acac)2) (0.1-0.6 atomic percent),with a seleneous acid (H2Se03) (0.1-0.7 atomic percent), in a oleyl amine (20-50 ml) to obtain a reaction solution;
(ii) adding a trioctylphosphine (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250'3C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of hexane and ethanol and drying at 60-120°C for 6-12 hrs to obtain a CoPd2Se2 nanoparticle.
19. The process as claimed in claim 11, wherein the Metal-based chalcogenide is Seis nanoparticle and obtained by the process comprising:
(i) mixing palladium acetylacetonate( Pd(acac)2) (0.1-0.6 atomic percent) with a seleneous acid (H2Se03) (0.-0.7 atomic percent), in a tetraethylene glycol (20-50 ml) to obtain a reaction solution;
(ii) adding a sodium borohydride (NaBH4) (0.6-5 ml) to the reaction solution;
(iii) heating the reaction solution of step (ii) for 2-6 h at a temperature in the range of 220-250°C to obtain a reaction product; and
(iv) washing the reaction product with a mixture of hexane and ethanol and drying at 60-120°C for 6-12 hrs to obtain a Pd17Se15 nanoparticles.
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