CN100428545C - Fuel cell catalyst modified by proton conductor and supported by conductive ceramics and its preparation - Google Patents

Abstract

A fuel cell catalyst modified by a proton conductor and supported by conductive ceramics and a preparation method thereof. Compared with the carbon black carrier catalyst, this catalyst has the following advantages: 1) It has good electrical conductivity and corrosion resistance; 2) The surface of the conductive ceramic has less micropores, and the precious metal catalyst particles can be anchored on the carrier surface, which improves the utilization rate of the catalyst ; 3) The proton-conducting high polymer can be used as a binder to improve the binding force between the metal particles of the catalyst and the carrier conductive ceramic; 4) The proton-conducting high polymer is a proton conductor, and the synthesized catalyst has the function of conducting protons. Therefore, the present catalyst is a multifunctional fuel cell catalyst. The preparation method is as follows: firstly prepare the catalyst nano noble metal colloid modified by the proton-conducting high polymer, and then deposit the colloid on the conductive ceramic carrier, and the average particle diameter of the catalyst noble metal is 2-5 nanometers. The fuel cell chip CCM is made of catalyst and assembled into a single cell, which has good electrical output performance.

Description

Fuel cell catalyst modified by proton conductor and supported by conductive ceramics and its preparation

technical field

The invention relates to a fuel cell catalyst, in particular to a fuel cell catalyst with the function of conducting protons. It is characterized in that the precious metal particles of the catalyst are modified by the proton conducting high polymer, and the carrier of the catalyst is conducting ceramics. The invention also relates to a preparation method of the catalyst.

Background technique

Proton Exchange Membrane Fuel Cell (PEMFC for short), as a new type of energy device, has many advantages such as low operating temperature, no pollution, high specific power, and rapid start-up, and has attracted more and more attention. It is a hot spot that countries all over the world are competing to study. The catalyst commonly used in fuel cells is the noble metal platinum or platinum alloys. However, platinum resources are scarce and expensive. Therefore, it is necessary to increase the utilization rate of platinum and reduce the amount of platinum used, so as to achieve the purpose of reducing the cost of fuel cells. At present, carbon black is generally used as a catalyst carrier, because carbon black has a high specific surface area, good electrical conductivity and a good pore structure, which is conducive to improving the particle dispersion of platinum metal. Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CN1165092C) used ammonium chloride, potassium chloride, etc. as anchors for chloroplatinic acid to prepare a Pt/C catalyst in which platinum particles were uniformly distributed in the pores of activated carbon and on the surface. The Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (CN1677729A) first prepared PtO _x colloids by colloidal method, and then performed gas phase reduction to prepare Pt/C catalysts with uniform particle size and high dispersion. Beijing University of Science and Technology (CN1243390C) first pretreated the carbon black carrier with a highly alkaline solution containing a weak reducing agent stannoic acid, so that the surface active points of the carbon black were evenly distributed; then added to the mixed solution of chloroplatinic acid and ruthenium chloride The PtRu/C catalyst was obtained by reduction deposition. However, the utilization rate of platinum in Pt/C and PtM/C prepared by the above method will not be very high. An important reason is that a large number of platinum or platinum alloy particles enter the micropores on the carbon surface. Or the platinum alloy cannot be in contact with the proton conductor, so it is difficult to form more three-phase reaction interfaces, thereby reducing the utilization rate of platinum. In addition, since platinum or platinum alloy is directly connected with carbon, the proton exchange resin cannot enter the position between platinum or platinum alloy and carbon during the process of preparing the membrane electrode. On the one hand, this reduces the three-phase reaction zone, and on the other hand, due to the lack of bonding, the bonding strength between platinum or platinum alloys and carbon is not high. In addition, in PEMFC, the durability of carbon black is weakened due to the harsh working environment of the catalyst. Moreover, the presence of platinum will accelerate the aging of carbon, thereby causing the shedding of platinum, which will also greatly reduce the durability of the catalyst.

It is also reported that carbon nanotubes (CNTs) are used as catalyst supports for fuel cells. CNT has a graphitized structure, so it has good electrical conductivity and chemical stability; at the same time, the degree of micropore development on the surface of the tube is low, and most of the platinum particles can be exposed on the surface of the tube, which improves the utilization of platinum; CNT has a tubular structure and The feature of one-dimensional extension and high mechanical strength can form an interpenetrating network structure in the catalytic layer, which not only improves the strength of the catalytic layer, but also enhances the electrical conductivity; in addition, it also has good thermal conductivity. But it should also be seen that the CNT surface is inert and lacks active sites. Therefore, the homogeneous dispersion of the metal catalyst is affected. Northern Jiaotong University (CN1414726A) used the photocatalytic in situ chemical reduction precipitation method to synthesize CNT-loaded platinum electrode catalysts, but did not fundamentally solve the problem of CNT agglomeration. Zhejiang University (CN1424150A) used microwave radiation heating method to support platinum-ruthenium alloy catalyst on the surface of carbon nanotubes. But their surface treatment of CNTs destroyed the chemical stability of CNTs. Although Xiamen University (CN1559686A) has solved the agglomeration problem of CNT to a certain extent, they also have the same problem to the surface treatment of CNT.

Ceramics usually have better chemical corrosion resistance, so if used as a catalyst carrier, they can have better corrosion resistance. However, ceramics are generally not conductive, so using them as catalyst supports cannot build electron channels for the catalyst layer. For this reason, the present invention adopts conductive ceramics as fuel cell catalyst carrier, and simultaneously uses proton-conducting high polymer to modify noble metal catalyst, and develops a fuel cell catalyst modified by proton conductor and using conductive ceramic as carrier. Compared with the background technology, the catalyst of the present invention has the following advantages: 1) it has good electrical conductivity; 2) it has excellent corrosion resistance; 3) the surface of the conductive ceramic has less micropores, and the catalyst noble metal particles can be anchored on the surface of the carrier. 4) The proton-conducting high polymer can be used as a binder to improve the bonding force between the catalyst metal particles and the carrier conductive ceramic, so that the durability of the catalyst is improved; 5) The proton-conducting high polymer itself is a proton conductor, and the synthesized catalyst also has Guide proton function.

At present, there are no related reports on fuel cell catalysts modified by proton conductors and supported by conductive ceramics.

Contents of the invention

The object of the present invention is to provide a fuel cell catalyst, especially a fuel cell catalyst with a proton-conducting function and a carrier of conductive ceramics. The invention also provides a preparation method of the catalyst.

The fuel cell catalyst of the present invention is a noble metal microparticle, and the characteristic is that the carrier is a conductive ceramic, and the catalytic noble metal microparticle loaded on the conductive ceramic carrier is modified by a proton-conducting high polymer.

The proton-conducting high polymer described in the present invention is perfluorosulfonic acid resin, sulfonated polysulfone resin, sulfonated polyphenylene sulfide resin (SPPS), sulfonated polybenzimidazole, sulfonated polyphosphazene, sulfonated Any of polyimide resin (SPI), sulfonated polystyrene resin, and sulfonated polyether ether ketone resin (S-PEEK).

The conductive ceramics described in the present invention are TiSi ₂ , TiB ₂ , TiC, SiC, PbTiO ₃ , Ti ₃ SiC ₂ , BaPbO ₃ , LaCrO ₃ , TiC/Si ₃ N ₄ or TiAl/TiB ₂ , with a particle size of 10-200 Nano.

The catalyst noble metal described in the present invention is noble metal alloy or noble metal simple substance,

Noble metal alloys are M _x N _y or M _x N _y O _z , where M, N, and O are Pt, Ru, Pd, Rh, Ir, Os, Fe, Cr, Ni, Co, Mn, Cu, Ti, Sn, respectively Any metal element in , V, Ga, and Mo, M, N, and O are different from each other, but at least one of them is the noble metal Pt, x, y, and z are natural numbers from 0 to 100, and x+y =100 or x+y+z=100;

The noble metal element is any one of Pt, Ru, Pd, Rh, Ir and Os.

The preparation method of the catalyst of the present invention is to firstly prepare the nano-scale noble metal particle colloid modified with the proton-conducting high polymer, and then load it on the conductive ceramic carrier to prepare the catalyst with the proton-conducting function. Concrete preparation method step is:

Step 1. Add the proton-conducting high polymer solution with a mass concentration of 1% to 10% into the alcohol-water mixture. After stirring, add the aqueous solution of the precursor salt of the catalyst, wherein the mass ratio of the noble metal to the proton-conducting high polymer is 1000～1:10, keep the pH of the solution at 8～13 during the reaction process, heat and reflux at 90～100°C for 10～50 minutes, and prepare the catalyst noble metal nanocolloid modified by the proton-conducting polymer;

Step 2. After fully dispersing the conductive ceramic particles, add them to the colloid solution prepared in Step 1, continue to stir for 1-2 hours, filter and dry to obtain a catalyst with the function of conducting protons.

The catalyst precursors of the present invention are H ₂ PtCl ₆ , RuCl ₃ , PdCl ₂ , RhCl ₃ , IrCl ₃ , OsCl ₃ , Fe(NO ₃ ) ₃ , Cr(NO ₃ ) ₃ , NiCl ₂ , Co(NO ₃ ) ₂ , MnCl ₂ , CuCl ₂ , TiCl ₃ , SnCl ₂ , VCl ₄ , Ga(NO ₃ ) ₃ or MoCl ₅ .

The mass ratio of alcohol to water in the alcohol-water mixture is 0.5-100:1, and the alcohol is any one of methanol, ethanol, propanol, ethylene glycol and isopropanol.

The prepared electrocatalyst was assembled into a single cell for electrical performance testing:

1. Preparation of fuel cell core chip CCM (catalyst coated membrane): add the prepared electrocatalyst to deionized water and 5% perfluorosulfonic acid resin solution, stir well, and adjust to a paste. Then evenly coated on both sides of the Nafion ^@ series film (NRE212 or NRE211, etc.) of DUPONT Company, and dried separately to obtain CCM.

2. Single cell assembly and testing: The carbon paper with polytetrafluoroethylene hydrophobic treatment is used as the gas diffusion layer, in which the mass content of polytetrafluoroethylene is 20% to 30%, and polytetrafluoroethylene and conductive carbon are compounded on one side The microporous layer composed of black particles (calcined at 350°C for 20 minutes), its main function is to optimize water and gas channels; the collector plate is a graphite plate with parallel grooves on one side; the end plate is a gold-plated stainless steel plate. The CCM, gas diffusion layer, collector plate, end plate and sealing material are assembled into a single cell. The single cell operating conditions are:

(1) Proton exchange membrane fuel cell (PEMFC): H ₂ /air, the air back pressure is 0; the anode is humidified, and the humidity is 0-100%; the operating temperature of the single cell is 60-80°C, and the humidification temperature is 60 ~75°C.

(2) Direct methanol fuel cell (DMFC): the concentration of methanol at the anode is 2 mol/liter, the flow rate is 5 ml/min, the cathode is air, and the back pressure is 0.

Compared with background technology, catalyst of the present invention is a kind of multifunctional fuel cell catalyst, has following advantage:

(1) Using conductive ceramics with stable chemical properties as the catalyst carrier can improve the corrosion resistance of the catalyst, thereby increasing the service life of the catalyst.

(2) The conductive ceramic particles with less micropores on the surface are used as the catalyst carrier, and the noble metal catalyst particles can be anchored on the surface of the carrier to improve the utilization rate of the catalyst metal.

(3) As a binder, the proton-conducting high polymer can improve the binding force between the metal particles of the catalyst and the conductive ceramic carrier, and improve the durability of the catalyst.

(4) The proton-conducting polymer itself is a proton conductor, and the synthesized catalyst also has the proton-conducting function.

Detailed ways

The present invention is described in detail below by way of examples.

Example 1

Get 116 mg of TiB ₂ conductive ceramic particles with a particle size of 10 nm to 50 nm and a purity greater than 95%, add it to 20 ml of a mixture of absolute ethanol and water, and the mass ratio of absolute ethanol to water is 1:1 , Ultrasonic (R-S150 ultrasonic cell pulverizer) dispersed for 5 minutes to obtain TiB ₂ conductive ceramic dispersion. Get 4 milliliters of Nafion ^@ solution with a mass concentration of 5% and add it to the mixed solution of 240 milliliters of absolute ethanol and water, the mass ratio of absolute ethanol and water is 1:1, after stirring for 10 minutes, add 40 milliliters of 4 g/L The H ₂ PtCl ₆ solution continued to stir, adjusted the pH of the solution to 8 with NaOH, and heated to reflux at 80°C. The solution gradually turned from light yellow to black, and finally dark black, and a stable Pt colloid was obtained. Then, the TiB ₂ conductive ceramic dispersion was added dropwise to the prepared Pt colloid, and the stirring was continued for 2 hours to obtain a Nafion ^@ modified 40% Pt/TiB ₂ catalyst. Among them, the average particle size of Pt is 2 nanometers, and the dispersion is very good.

Preparation of the fuel cell core chip CCM: add the prepared catalyst to deionized water and a 5% perfluorosulfonic acid resin solution, stir well, and make a paste. Then evenly coated on both sides of Nafion ^@ series film NRE211 of DU PONT company, and dried to obtain CCM. The total loading of Pt in the catalytic layers of the cathode and anode of the CCM is 0.42 mg/cm ² .

Single cell assembly and testing: The carbon paper with polytetrafluoroethylene hydrophobic treatment is used as the gas diffusion layer. Pore layer (calcined at 350°C for 20 minutes), its main function is to optimize water and gas channels; the collector plate is a graphite plate with parallel grooves on one side; the end plate is a gold-plated stainless steel plate. The CCM, gas diffusion layer, collector plate, end plate and sealing material are assembled into a single cell. The operating conditions of the single cell are: H ₂ /air, the air back pressure is 0, the anode is 100% humidified, the operating temperature of the single cell is 70°C, and the humidification temperature is 70°C. The test results show that the electrical output of the single cell reaches 0.801 volts/cm ² @300 mA/cm ² .

Example 2

Get 116 mg of TiC conductive ceramic particles with a particle size of 50-100 nanometers and a purity greater than 92%, add it to a mixture of 20 ml of isopropanol and water, the mass ratio of isopropanol to water is 1:1, and ultrasonically (R -S150 Ultrasonic Cell Pulverizer) to disperse for 10 minutes to obtain a TiC conductive ceramic dispersion. Get 4 milliliters of sulfonated polyphenylene sulfide resin (SPPS) solution with a mass content of 5% and add it to a mixed solution of 240 milliliters of isopropanol and water. The mass ratio of isopropanol and water is 1:1. After stirring for 5 minutes, add Continue to stir 40 ml of 4 g/L H ₂ PtCl ₆ solution, adjust the pH of the solution to 10 with NaOH, and heat to reflux at 100°C. The solution gradually turns from light yellow to black, and finally becomes dark black, and a stable Pt colloid is obtained. . Then, the TiC conductive ceramic dispersion liquid was added dropwise into the prepared Pt gel, and the stirring was continued for 3 hours to obtain the SPPS-modified 40% Pt/TiC catalyst. Among them, the average particle size of Pt is 3 nanometers, and the dispersion is very good. The preparation process of the fuel cell core chip CCM, single cell assembly and test conditions are the same as in Example 1, and the catalyst prepared in this example is used. The test results show that the electrical output of the single cell reaches 0.765 volts/cm ² @300 mA/cm ² .

Example 3

Get 116 mg of BaPbO ₃ conductive ceramic particles with a particle size of 100 to 120 nanometers and a purity greater than 90%, add it to a mixture of 20 ml of methanol and water, the mass ratio of methanol to water is 100:1, and ultrasonically (R- S150 ultrasonic cell pulverizer) dispersed for 6 minutes to obtain BaPbO ₃ conductive ceramic dispersion. Get 4 milliliters of sulfonated polyimide resin (SPI) solutions with a mass content of 5% and add them to a mixed solution of 240 milliliters of methanol and water. The mass ratio of methanol and water is 100:1. After stirring for 6 minutes, add 40 milliliters Continue to stir the 4 g/L H ₂ PtCl ₆ solution, adjust the pH of the solution to 9 with NaOH, and heat to reflux at 90°C. The solution gradually turns from light yellow to black, and finally dark black, and a stable Pt colloid is obtained. Then the BaPbO ₃ conductive ceramic dispersion was added dropwise to the prepared Pt gel, and the stirring was continued for 3 hours to obtain the SPI-modified 40% Pt/BaPbO ₃ catalyst. Among them, the average particle size of Pt is 4 nanometers, and the dispersion is very good. The preparation process of the fuel cell core chip CCM, single cell assembly and test conditions are the same as in Example 1, and the catalyst prepared in this example is used. Test results show that the electrical output of the single cell reaches 0.785 volts/cm ² @300 mA/cm ² .

Example 4

Get 116 milligrams of TiAl/TiB ₂ conductive ceramic microparticles, particle diameter 120～150 nanometers, purity greater than 92%, join in the mixed solution of 20 milliliters of dehydrated alcohol and water, the mass ratio of dehydrated alcohol and water is 1: 1. Ultrasonic (R-S150 Ultrasonic Cell Pulverizer) disperses for 10 minutes to obtain a TiAl/TiB ₂ conductive ceramic dispersion. Take 4 milliliters of 5% sulfonated polyether ether ketone resin (S-PEEK) solution and add it to a mixture of 240 milliliters of absolute ethanol and water, the mass ratio of absolute ethanol and water is 1:1, stir for 8 Minutes later, add 40 ml of 4 g/L H ₂ PtCl ₆ solution, 40 ml of 4 g/L RuCl ₃ solution, continue to stir, adjust the pH of the solution to 11 with NaOH, and heat to reflux at 100 ° C. The solution gradually changes from light yellow to reflux. It turns black, and finally becomes dark black, and a stable PtRu colloid is obtained. Then the TiAl/TiB ₂ conductive ceramic dispersion liquid was added dropwise to the prepared PtRu gel, and the stirring was continued for 2 hours to prepare the S-PEEK modified 40% Pt ₅₀ Ru ₅₀ /TiAl-TiB ₂ catalyst. Among them, the average particle diameter of the metal particles is 5 nanometers, and the dispersibility is very good.

Preparation of the fuel cell core chip CCM: add the prepared electrocatalyst to deionized water and a 5% perfluorosulfonic acid resin solution, stir well, and make a paste. Then evenly coated on both sides of Nafion ^@ series film NRE211 of DU PONT company, and dried to obtain CCM. The anode uses the self-made catalyst of the present invention with a Pt loading of 1 mg/cm ² , and the cathode uses a Pt/C catalyst from JM Company with a Pt loading of 1 mg/cm ² .

Single cell assembly and testing: The carbon paper with polytetrafluoroethylene hydrophobic treatment is used as the gas diffusion layer, in which the mass content of polytetrafluoroethylene is 30%, and a microporous layer composed of PTFE and conductive carbon black particles is compounded on one side. (calcined at 350°C for 20 minutes), its main function is to optimize water and gas channels; the collector plate is a graphite plate with parallel grooves on one side; the end plate is a gold-plated stainless steel plate. The CCM, gas diffusion layer, collector plate, end plate and sealing material are assembled into a single cell. The operating conditions of the single cell are: the concentration of methanol at the anode is 2 mol/L, the flow rate is 5 ml/min, the cathode is air, and the back pressure is 0. Test results show that the electrical output of the single cell reaches 245mW/ ^cm2 @400mA/ ^cm2 .

Example 5

Get 116 mg of TiC/Si ₃ N ₄ conductive ceramic particles with a particle size of 150 to 200 nanometers and a purity greater than 85%, and add it to a mixture of 20 ml of absolute ethanol and water. The mass ratio of absolute ethanol to water is 1:1, ultrasonic (R-S150 ultrasonic cell pulverizer) dispersion for 5 minutes to obtain TiC/Si ₃ N ₄ conductive ceramic dispersion. Get 4 milliliters of Nafion ^@ solution with a mass content of 5% and add it to a mixture of 240 milliliters of absolute ethanol and water. The mass ratio of absolute ethanol and water is 1:1. After stirring for 10 minutes, add 40 milliliters of 4 g/L H ₂ PtCl ₆ solution, 20 ml 4 g/L RuCl ₃ solution, 20 ml 4 g/L SnCl ₃ solution, continue to stir, adjust the pH of the solution with NaOH to 9, and heat to reflux at 100 ° C. The solution turns from light yellow to Gradually darkens and finally dark black to obtain a stable colloid. Then the TiC/Si ₃ N ₄ conductive ceramic dispersion was added dropwise to the prepared colloid, and the stirring was continued for 2 hours to obtain a Nafion ^@ modified 40% Pt _5o Ru ₂₅ Sn ₂₅ /TiC/Si ₃ N ₄ catalyst. Among them, the average particle diameter of the metal particles is 4.5 nanometers, and the dispersion is very good. The preparation process, single cell assembly and test conditions of the fuel cell core chip CCM are the same as in Example 4, and the catalyst prepared in this example is used. The test results show that the electrical output of the single cell reaches 276 mW/cm ² @400 mAh/cm ² .

Claims (3)

1. A fuel cell catalyst, the catalyst is a noble metal particle, characterized in that the carrier is a conductive ceramic, and the catalyst noble metal particle loaded on the conductive ceramic carrier is modified by a proton-conducting polymer, wherein the proton-conducting polymer The material is any one of perfluorosulfonic acid resin, sulfonated polyphenylene sulfide resin, sulfonated polyimide resin and sulfonated polyether ether ketone resin; the conductive ceramics are TiB ₂ , TiC, BaPbO ₃ , TiC/Si ₃ N ₄ or TiAl/TiB ₂ , the particle size is 10-200 nanometers. 2. The fuel cell catalyst according to claim 1, wherein the catalyst noble metal is a noble metal alloy or a noble metal element, Noble metal alloys are M _x N _y or M _x N _y O _z , where M, N, and O are Pt, Ru, Pd, Rh, Ir, Os, Fe, Cr, Ni, Co, Mn, Cu, Ti, Sn, respectively Any metal element in , V, Ga, and Mo, M, N, and O are different from each other, but at least one of them is the noble metal Pt, x, y, and z are natural numbers from 0 to 100, and x+y =100 or x+y+z=100; The noble metal element is any one of Pt, Ru, Pd, Rh, Ir and Os. 3. The preparation method of the fuel cell catalyst according to claim 1, characterized in that the preparation steps are: Step 1. Add the proton-conducting high polymer solution with a mass concentration of 1% to 10% into the alcohol-water mixture. After stirring, add the aqueous solution of the catalyst precursor salt, wherein the mass ratio of the noble metal to the proton-conducting high polymer is 1000-1:10, during the reaction, the pH of the solution is 8-13, heated and refluxed at 90-100°C for 10-50 minutes, and the catalyst noble metal nanocolloid modified by the proton-conducting polymer is prepared; Step 2. After fully dispersing the conductive ceramic particles, add them to the colloid solution prepared in Step 1, continue to stir for 1 to 2 hours, filter and dry to obtain a catalyst; The mass ratio of alcohol to water in the alcohol-water mixture is 0.5-100:1, and the alcohol is any one of methanol, ethanol and isopropanol.