CN111933961A - Binary CoFe alloy loaded g-C3N4Catalyst and preparation method thereof - Google Patents

Abstract

The invention provides a binary CoFe alloy supported g-C ₃ N ₄ catalyst and a preparation method thereof, comprising the following steps: synthesizing sheet-like two-dimensional porous g-C ₃ N ₄ and dispersing in deionized water; , cobalt salt and iron salt are respectively dispersed in deionized water; 2-methylimidazole and polyvinylpyrrolidone are dispersed in deionized water; the solutions of step S1, step S2 and step S3 are mixed, and after water bath reaction and room temperature stirring, After centrifugation and vacuum drying, CoFe@g-C ₃ N ₄ was obtained; the obtained CoFe@g-C ₃ N ₄ was placed in a tube furnace and calcined to obtain a g-C ₃ N ₄ -loaded Co/CoFe-NC@g- _C3N4 material _. The Co/CoFe-NC@g-C ₃ N ₄ material is obtained by adopting the technical scheme of the present invention, which has good catalytic activity, stability and durability compared with commercial Pt/C and RuO ₂ , and the preparation process is simple and controllable.

Description

Binary CoFe alloy supported g-C3N4 catalyst and preparation method thereof

technical field

_The invention belongs to the technical field of catalysts, and in particular relates to a binary CoFe alloy supported _gC3N4 catalyst and a preparation method thereof.

Background technique

The increasingly serious energy crisis has put forward high requirements for environmentally friendly, safe and reliable new energy conversion systems with high energy density. Current promising energy systems include metal-air batteries (MABs), fuel cells, and metal-ion batteries. Among them, zinc-air battery, as a kind of fuel cell, has attracted much attention because of its high theoretical energy density and high earth reserves. The key to zinc-air battery (ZAB) technology is to develop efficient and stable electrocatalysts for cathodic oxygen reduction reaction (ORR) and anodic oxygen evolution reaction (OER).

The current commercial catalysts for ORR and OER on ZAB are noble metal-based Pt/C and _IrO2 /RuO2 catalysts, respectively, but their large _- scale applications are limited due to cost and stability issues. Therefore, the development of low-cost, highly active bifunctional electrocatalysts is of great significance for the future technological development of fuel cells.

Various non-noble metal-based catalysts containing carbon supports have been developed for ORR and OER. The results show that non-metallic elements (N, S, O, and P, etc.) doped carbon or transition metal (Co, Fe, Ni, and Zn, etc.)-based catalysts have better catalytic activity, which is attributed to their heteroatom doping. and modified electronic structures. Among all catalysts, cobalt-based catalysts have attracted extensive attention. Co in the form of metallic Co on carbonaceous supports, Co-M alloys, and Co-Nx were all confirmed to possess active sites for ORR and OER. In fact, they can effectively tune the electronic structure of carbon-containing supports and reduce the adsorption energy of intermediates, thereby reducing the overpotentials of ORR and OER. In addition, the electrocatalytic performance can be further improved by the electronic synergistic effect between metal elements based on binary or ternary component catalysts. However, the current synthesis of CoFe catalysts is through a high energy consumption route, and it is difficult to simultaneously achieve the miniaturization of metal particles, and it is difficult to suppress their migration and aggregation.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention discloses a binary CoFe alloy supported g-C ₃ N ₄ catalyst and a preparation method thereof, which have efficient dual functions of oxygen reduction and oxygen evolution, and can avoid the agglomeration of nano metal particles.

To this, the technical scheme adopted in the present invention is:

A preparation method of a binary CoFe alloy supported g _{- C3N4} catalyst, comprising the following steps:

Step S1, synthesizing sheet-like two-dimensional porous g-C ₃ N ₄ and dispersing in deionized water;

Step S2, disperse zinc salt, cobalt salt, iron salt in deionized water respectively;

Step S3, 2-methylimidazole and polyvinylpyrrolidone are dispersed in deionized water;

In step S4, the solutions of step S1, step S2 and step S3 are mixed, subjected to water bath reaction and room temperature stirring, centrifuged, and vacuum dried to obtain CoFe@gC ₃ N ₄ ;

In step S5, the obtained CoFe@gC ₃ N ₄ is calcined in a tube furnace to obtain a Co/CoFe-NC@gC ₃ N ₄ material supported by gC ₃ N ₄ .

Using this technical scheme, the zinc metal zeolite imidazole compound, Co ²⁺ and Fe ³⁺ and gC ₃ N ₄ are hydrothermally synthesized by a one-pot method, combined with processes such as tube furnace sintering, and prepared on gC ₃ N ₄ nanosheets Highly dispersed, highly catalytically active Co nanoparticles and CoFe alloys for Zn _- air battery reactions with ORR at the cathode and OER at the anode, compared to commercial Pt/C and RuO2, this binary CoFe alloy supports g- The C ₃ N ₄ catalyst has good catalytic activity, stability and durability.

As a further improvement of the present invention, in step S1, the sheet-like two-dimensional porous gC ₃ N ₄ is synthesized by the following steps: placing melamine in a crucible, heating at 550° C. for 2 h in a muffle furnace, and then Heating at 500 °C for ₂ h, the sheet-like porous _gC3N4 material was obtained.

As a further improvement of the present invention, in step S2, the mol ratio of the zinc salt and the cobalt salt is 1: 0.8-1.2. Further, the molar ratio of the zinc salt and the cobalt salt is 1:1.

As a further improvement of the present invention, in step S2, the zinc salt is zinc nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, and the iron salt is iron nitrate nonahydrate.

As a further improvement of the present invention, the molar ratio of the 2-methylimidazole to the zinc salt is 1.5-2.5:1. Further, the molar ratio of the 2-methylimidazole to the zinc salt is 2.1:1.

As a further improvement of the present invention, in step S4, the temperature of the water bath is 50-70°C, the time of the water bath is 1-4h; the stirring time at room temperature is 6-14h, and the stirring speed is 650 rpm.

As a further improvement of the present invention, in step S4, the rotational speed of centrifugal separation is 6000-10000 rpm, and deionized water is used for washing at least twice; the temperature of vacuum drying is 60-80 °C, and the drying time is 10-14 h.

As a further improvement of the present invention, in step S5, the calcination is performed in an inert gas atmosphere, the calcination temperature is 800-1000°C, and the calcination time is 1-3 h.

The invention also discloses a binary CoFe alloy supported g-C _{3 N 4 catalyst, which is prepared by using the preparation method of the binary CoFe alloy supported g- C 3 N 4 catalyst} as described in any one of the above.

The invention also discloses the application of the above-mentioned binary CoFe alloy supported g-C ₃ N ₄ catalyst, which is used as a catalyst in a zinc-air battery.

Compared with the prior art, the beneficial effects of the present invention are:

The technical scheme of the present invention adopts a one-pot method to synthesize Co/CoFe-NC@gC ₃ N ₄ material from the bottom up, and the obtained material is based on a porous two-dimensional gC ₃ N ₄ material with abundant N coordination sites, which is beneficial to The uniform distribution and growth of nano-scale Co nanoparticles and CoFe alloys have good catalytic activity, stability and durability compared with commercial Pt/C and RuO ₂ ; and the method is simple in preparation process, abundant and controllable in raw materials, and has a relatively high performance. High scale production value.

Description of drawings

FIG. 1 is a schematic diagram of the preparation method of Example 3 of the present invention.

2 is the X-ray diffraction pattern of the products obtained in Example 1, Example 2 and Example 3 of the present invention.

3 is a Raman diagram of the products obtained in Example 1, Example 2, and Example 3 of the present invention.

4 is a scanning electron microscope image of Co/CoFe-NC@gC ₃ N ₄ obtained in Example 3 of the present invention.

5 is a transmission electron microscope image of Co/CoFe-NC@gC ₃ N ₄ obtained in Example 3 of the present invention.

FIG. 6 is a graph comparing the oxygen reduction polarization curves of the catalysts prepared in Example 1, Example 2, and Example 3 of the present invention and commercial Pt/C.

FIG. 7 is a comparison diagram of the oxygen reduction stability cyclic voltammetry curves of the catalyst prepared in Example 3 of the present invention and commercial Pt/C.

FIG. 8 is a graph comparing the oxygen evolution polarization curves of the catalysts prepared in Example 1, Example 2, and Example 3 of the present invention and commercial RuO ₂ .

9 is a cyclic voltammetry diagram of oxygen evolution stability of the catalyst prepared in Example 3 of the present invention and commercial RuO ₂ .

FIG. 10 is a cycle stability test chart of the catalyst prepared in Example 3 of the present invention and the zinc-air battery assembled with commercial Pt/C+RuO ₂ .

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below by way of examples. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The invention provides a preparation method based on ZIF-derived binary CoFe alloy supported on gC ₃ N ₄ bifunctional catalyst, comprising the following steps:

Step S1, synthesis of sheet-like two-dimensional porous gC ₃ N ₄ : 10 g of melamine was placed in an alumina crucible with a lid, and heated at 550° C. for 2 h and then 500° C. for 2 h in a muffle furnace, and the heating rate was 5 ℃/min, dispersed in 15ml deionized water.

Step S2, 15 mmol of zinc nitrate hexahydrate, 15 mmol of cobalt nitrate hexahydrate and a certain mass of ferric nitrate nonahydrate are dispersed in 120 ml of deionized water.

In step S3, 32 mmol of 2-methylimidazole and 0.5 g of polyvinylpyrrolidone were dispersed in 80 ml of deionized water.

In step S4, the solutions of step S1, step S2 and step S3 are mixed, a 60-degree water bath is performed for 3 hours, and the room temperature is stirred for 12 hours, and the stirring speed is 650 rpm; The product CoFe@gC ₃ N ₄ was vacuum dried at 60 °C for 12 h.

In step S5, the obtained CoFe@gC ₃ N ₄ is calcined in a tube furnace to obtain a Co/CoFe-NC@gC ₃ N ₄ material supported by gC ₃ N ₄ . During the calcination process, a N ₂ atmosphere is maintained, and the calcination temperature is 900 °C, the calcination time was 2 h, and the heating rate was 5 °C/min.

The present invention will be further described below through specific examples using the above-mentioned preparation method.

Example 1

The preparation of Co-NC materials adopts the following steps: (1) Synthesis of Co-ZIF

Dissolve 4.462 g of zinc nitrate hexahydrate and 4.365 g of cobalt nitrate hexahydrate in 120 mL of deionized water to form a clear solution. At the same time, 2.624 g of 2-methylimidazole and 0.5 g of polyvinylpyrrolidone were dissolved in another 80 mL of deionized water to form a clear solution. Finally, the two solutions were thoroughly mixed, and the two solutions were thoroughly mixed, and the water bath was 60 degrees for 3 h, and stirred at room temperature for 12 h at 650 rpm. . The product was washed three times with deionized water, dried under vacuum at 60 °C for 12 h, and recorded as Co-ZIF.

(2) Synthesis of Co-NC

An appropriate amount of the above product was weighed and placed in a tube furnace, under nitrogen protection, heated to 900 °C at a heating rate of 5 °C/min and held for 2 h to obtain the final sample, denoted as Co-NC.

Example 2

The preparation of Co/CoFe-NC materials adopts the following steps:

(1) Synthesis of CoFe-ZIF

Dissolve 4.462 g of zinc nitrate hexahydrate, 4.365 g of cobalt nitrate hexahydrate and 0.101 g of ferric nitrate nonahydrate in 120 mL of deionized water to form a clear solution. At the same time, 2.624 g of 2-methylimidazole and 0.5 g of polyvinylpyrrolidone were dissolved in another 80 mL of deionized water to form a clear solution. Finally, the two solutions were thoroughly mixed, and the two solutions were fully mixed, and the water bath was at 60 degrees for 3 h, and stirred at room temperature at 650 rpm for 12 h. . The product was washed three times with deionized water, dried under vacuum at 60 °C for 12 h, and recorded as CoFe-ZIF.

(2) Synthesis of Co/CoFe-NC

An appropriate amount of the above product was weighed and placed in a tube furnace, under nitrogen protection, heated to 900 °C at a heating rate of 5 °C/min and held for 2 h to obtain the final sample, denoted as Co/CoFe-NC.

Example 3

_The preparation of Co/CoFe-NC@ _gC3N4 , as shown in Fig. 1, includes the following steps:

(1) Synthesis of gC ₃ N ₄

10 g of melamine was placed in an alumina crucible with a lid, heated at 550 °C for 2 h and then 500 °C for 2 h in a muffle furnace, and the heating rate was 5 °C/min to obtain gC ₃ N ₄ , which was dispersed in 15 ml deionized water.

( ₂ ) Synthesis of CoFe@ _gC3N4

4.462 g of zinc nitrate hexahydrate, 4.365 g of cobalt nitrate hexahydrate and 0.101 g of ferric nitrate nonahydrate were dissolved in 120 mL of deionized water to form a clear solution. At the same time, 2.624 g of 2-methylimidazole and 0.5 g of polyvinylpyrrolidone were dissolved in another 80 mL of deionized water to form a clear solution. Finally, these two solutions were thoroughly mixed with the solution in step 1, 60 degrees water bath for 3h, at 650 Stir at room temperature for 12 h at rpm. The product was washed three times with deionized water, dried under vacuum at 60 °C for 12 h, and recorded as CoFe@gC ₃ N ₄ .

(3) Synthesis of Co/CoFe-NC@gC ₃ N ₄

An appropriate amount of the above product was weighed and placed in a tube furnace, under nitrogen protection, heated to 900 °C at a heating rate of 5 °C/min and held for 2 h to obtain the final sample, denoted as Co/CoFe-NC@gC ₃ N ₄ .

The X-ray diffraction patterns of the catalyst products obtained in Examples 1 to 3 are shown in Figure 2, the Raman diagrams of the catalyst products obtained in Examples 1 to 3 are shown in Figure 3, and the Co obtained in Example 3 is shown in Figure 3. The SEM image of /CoFe-NC@gC ₃ N ₄ is shown in Fig. 4, and the TEM image is shown in Fig. 5.

The properties of the catalytic materials prepared in the above examples are tested below.

Electrochemical tests were performed using a three-electrode system, the counter electrode was a platinum sheet, the reference electrode was an Ag/AgCl electrode, and the working electrode was a glassy carbon electrode coated with a catalyst, wherein the catalyst was Example 1-3, and the commercial catalyst was Pt /C and RuO ₂ . When testing ORR and OER, the electrolytes are both 0.1 M KOH aqueous solution, but the electrolyte required for ORR needs to be saturated with oxygen. The preparation steps of the catalyst thin layer on the electrode are as follows: take 4 mg of catalyst, add 300 μL ethanol and 100 μL Nafion solution (0.5 wt.%), ultrasonically disperse for 30 min, and use a 10 μL pipette to take 4 μL of uniformly dispersed suspension droplets On the smooth glassy carbon electrode, it can be tested after infrared drying. The electrochemical performance test results are shown in Figure 6-9.

From the ORR curves obtained for different catalysts in oxygen-saturated 0.1 M KOH solution in Fig. 6, it can be seen that among the four catalysts including commercial Pt/C, the catalyst Co/CoFe-NC@gC ₃ N ₄ exhibited the best The best ORR performance with a half-wave potential of 0.87 V and a diffusion-limited current density of 5.90 mA cm ^-2 surpasses that of a commercial 20% Pt/C catalyst (half-wave potential of 0.85 V). Compared with Co@NC, Co/CoFe@NC has better ORR performance when Co is doped with a small amount of Fe, which confirms that the added Fe element promotes the formation of the bimetallic electronic synergy between Co and Fe, Thereby improving ORR performance. _In addition, Co/CoFe@ _gC3N4 achieves better ORR performance compared with Co/CoFe@NC, which confirms the key optimization role of _{gC3N4 .}

It can be seen from Fig. 7 that after 2000 cycles under the same conditions, the potential shift of the catalyst Co/CoFe@ _gC3N4 is only ₃ mV, while that of commercial Pt/C is about 12 mV, which indicates that under alkaline conditions _The lower electrode material Co/CoFe@ _gC3N4 possesses better ORR stability than commercial Pt/C catalysts.

From the OER curves obtained for different catalysts in oxygen-saturated 0.1 M KOH solution in Fig. 8, it can be seen that among the _four catalysts including commercial RuO2, the catalyst Co/CoFe _- NC@ _gC3N4 exhibited an optimal The OER performance of 1.64 V required for potentiometric water oxidation at a current density of 10 mA cm _- ² far exceeds that of commercial RuO catalysts (1.69 V).

Figures 9 and 10 are the relevant performance tests of the catalyst prepared in Example 3. Figure 9 is a comparison diagram of the oxygen evolution stability cyclic voltammetry curves of the Co/CoFe-NC@gC ₃ N ₄ catalyst obtained in Example 3 and commercial RuO ₂ . It can be seen from Figure 9 that after 2000 CV cycles, Co The decay of the OER potential of /CoFe@gC ₃ N ₄ is only 2 mV, while that of RuO ₂ reaches 14 mV, which means that Co/CoFe@gC ₃ N ₄ has excellent OER stability.

Since Co/CoFe@gC ₃ N ₄ exhibits excellent bifunctional catalytic activity for ORR and OER, it can be used as a cathode material to assemble rechargeable Zn-air batteries. The performance test of zinc-air battery was evaluated by self-made battery, and the electrolyte was mixed with 6 mol KOH electrolyte and 0.2 mol zinc acetate solution. Specifically, a polished zinc plate (0.08 mm thick) was used as the anode, and a catalyst-modified carbon cloth was used as the cathode with an active area of ~1 cm ² . Experimental comparison catalysts were prepared from commercial Pt/C and RuO ₂ (mass ratio=1:1). The zinc-air battery was tested using the cyclic galvanostatic pulse method, subjected to 5 min galvanostatic discharge and charge cycles at a current density of 5 mA cm ^-2 .

The catalyst prepared in Example 3 was assembled into a zinc-air battery for open-circuit voltage measurement. The open-circuit potential of the battery assembled based on Co/CoFe@gC ₃ N ₄ was 1.505 V, which was at a high level among other non-precious metal catalysts.

Figure 10 is the cycle stability test chart of the catalyst prepared in Example 3 and the commercialized Pt/C+RuO ₂ assembled Zn-air battery. It can be seen that the battery can last for about 110 h (660 charge/discharge cycles), while The commercial Pt/C ₊ RuO2 can only be maintained for ₁₄ h (about 84 charge/discharge cycles), which indicates that Co/CoFe@ _gC3N4 has excellent battery cycling stability. According to the above experimental results, we believe that the Zn-air battery based on Co/CoFe@gC ₃ N ₄ catalyst has great commercial potential, even surpassing the current commercial catalyst Pt/C+RuO ₂ .

Compared with other materials, the material of Example 3 Co/CoFe-NC@gC ₃ N ₄ used in zinc-air batteries is characterized by the fact that the evaporation of zinc metal creates more channels, which exposes more active sites. ; The sheet-like gC ₃ N ₄ support has abundant N coordination sites, which provides a substrate for the uniform distribution of Co/CoFe nanoparticles; the synergistic effect of cobalt-iron binary metal further improves the electrochemical performance of the material. In addition, the cobalt iron particles wrapped by the carbon layer can effectively inhibit corrosion and further improve the catalytic stability of the material. The material was modified on a glassy carbon electrode, and tested by cyclic voltammetry and linear sweep voltammetry, the half-wave potential of oxygen reduction of the optimal material was 0.87 V, and the voltage of oxygen evolution at a current density of 10 mA cm ⁻² It is 1.64 V, which is superior to the catalytic activity and durability of commercial platinum/carbon and ruthenium oxide catalysts, respectively, and has good application prospects. In addition, the optimal materials were assembled into liquid zinc-air batteries with excellent cyclability and power density.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. Binary CoFe alloy loaded g-C₃N₄The preparation method of the catalyst is characterized by comprising the following steps:

step S1, synthesizing sheet-shaped two-dimensional porous g-C₃N₄And dispersed in deionized water;

step S2, respectively dispersing zinc salt, cobalt salt and iron salt in deionized water;

step S3, dispersing 2-methylimidazole and polyvinylpyrrolidone in deionized water;

step S4, mixing the solutions obtained in the steps S1, S2 and S3, performing water bath reaction, stirring at room temperature, centrifuging, and drying in vacuum to obtain CoFe @ g-C₃N₄；

Step S5, obtaining CoFe @ g-C₃N₄Calcining in a tubular furnace to obtain g-C₃N₄Supported Co/CoFe-NC @ g-C₃N₄A material.

2. The binary CoFe alloy loaded g-C of claim 1₃N₄A method for producing a catalyst, characterized in that, in step S1, the sheet-like two-dimensional porous g-C₃N₄The preparation method comprises the following steps: placing melamine in a crucible, heating at 550 deg.C for 2 h in a muffle furnace, and heating at 500 deg.C for 2 h to obtain sheet-like porous g-C₃N₄A material.

3. The binary CoFe alloy loaded g-C of claim 1₃N₄The preparation method of the catalyst is characterized by comprising the following steps: in step S2, the molar ratio of zinc salt to cobalt salt is 1: 0.8-1.2.

4. The binary CoFe alloy loaded g-C of claim 3₃N₄The preparation method of the catalyst is characterized by comprising the following steps: in step S2, the zinc salt is zinc nitrate hexahydrate, the cobalt salt is cobalt nitrate hexahydrate, and the iron salt is ferric nitrate nonahydrate.

5. The binary CoFe alloy loaded g-C of claim 4₃N₄The preparation method of the catalyst is characterized by comprising the following steps: the molar ratio of the 2-methylimidazole to the zinc salt is 1.5-2.5: 1.

6. the binary CoFe alloy loaded g-C of claim 1₃N₄The preparation method of the catalyst is characterized by comprising the following steps: in the step S4, the temperature of the water bath is 50-70 ℃, and the time of the water bath is 1-4 h; stirring time at room temperature is 6-14h, and stirring speed is 650 rpm.

7. The binary CoFe alloy of claim 6 loaded g-C₃N₄The preparation method of the catalyst is characterized by comprising the following steps: in step S4, the rotation speed of centrifugal separation is 6000-10000rpm, and deionized water is adopted for washing at least 2 times; the temperature of vacuum drying is 60-80 ℃, and the drying time is 10-14 h.

8. The binary CoFe alloy of any of claims 1 to 7 loaded with g-C₃N₄The preparation method of the catalyst is characterized by comprising the following steps: in the step S5, the calcination is performed in an inert gas atmosphere at a temperature of 800-1000 ℃ for 1-3 h.

9. Binary CoFe alloy loaded g-C₃N₄A catalyst, characterized by: adopting the binary CoFe alloy as 1-8 to load g-C₃N₄The catalyst is prepared by the preparation method.

10. The binary CoFe alloy loaded g-C of claim 9₃N₄The application of the catalyst is characterized in that: it is used as a catalyst in zinc-air batteries.

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