Preparation And Performance Study Of Pt₃Cu Catalyst Supported On Polypyrrole Modified Carbon Carrier

Platinum based catalysts occupy a dominant position in the catalysts of proton exchange membrane fuel cells.The carrier used for commercial Pt/C catalysts is traditional carbon black,which has the disadvantages of easy corrosion,small specific surface area,and surface passivation unfavorable to metal loading.resulting in a rapid decrease in the activity of platinum（Pt）catalysts and a short service life.in order to improve the utilization rate and life of platinum atoms,a solution was sought from the support material of Pt catalyst.It is optimized in terms of morphology,specific surface area and functional degree to increase the interaction between the carrier and the metal,achieve the purpose of regulating the performance of the active metal components,increase the dispersion and anchoring effect of the metal,and improve the catalytic activity and service life.Based on the excellent stability and specific surface area of polypyrrole conductive material,the overall performance of the catalyst was optimized when it was applied to the support material.The research content is as follows:（1）In order to expand the specific surface area of the support and optimize the pore structure,the mesoporous silica template was used to coat the polypyrrole shell,and three kinds of carbonized mesoporous hollow support with different morphologies and pore characteristics were prepared,and the influence of different shell thickness on the performance of the catalyst was explored.The unique hollow mesoporous structure has a large specific surface area,which can provide a broad growth area for the active site,and provide suitable pore diameter and pore structure.Meanwhile,the optimized mesoporous structure can shorten the diffusion length,making the reaction medium more effectively contacting the internal active site,and improving the mass transfer efficiency.The surface area of C-HCS was 721 m²/g,which is much higher than that of carbon black（318 m²/g）.The pore size distribution is about 3.5 nm.The mass activity（MA）of Pt₃Cu/C2-HCS with a shell thickness of about 14 nm was 0.46 A mg _Pt^-1,which was 4.2 times that of JM Pt/C(0.11 A mg _Pt^-1).The half-wave potential(E_1/2)of JM Pt/C was negative 39 m V after stability test（ADT）.The negative shift of Pt₃Cu/C2-HCS is only 12 m V,and the maximum battery power was 742 m W/cm².（2）Improving the passivation state of carbon black surface can increase the interaction between the carrier and the metal,which can improve the stability of the catalyst.Pyrrole was polymerized in situ on carbon black surface at low temperature to prepare functionalized modified carbon carrier,and the modification difference of different pyrrole addition levels on carbon black was investigated.After the polymerization of pyrrole,oxygen-containing functional groups were introduced on the surface of carbon black to promote the electron transfer between nitrogen and carbon,thus adjusting the crystal structure of carbon black and the electronic structure of C atom.The carrier performance optimization enhanced the interaction between pyrrole and metal,thus inhibiting the dissolution and shedding of metal components under carbon corrosion,and improving the stability.The electrochemical activity area of Pt₃Cu/C@0.4-PPy catalyst(112.04 m² g _Pt^-1)was much larger than that of JM Pt/C(76.190 m² g _Pt^-1),and it shows excellent MA(0.506 A mg _Pt^-1)and specific activity(0.45 m A cm _Pt^-2).After ADT,E_1/2 only shifted negative 6 m V,and the stability of catalyst was greatly improved.（3）In order to regulate the local coordination environment,defects were introduced to increase the number of active sites.N and S double doped modified carbon carrier was prepared by polymerization of pyrrole on carbon black surface with p-methylbenzene sulfonic acid dopant.Compared with the single doped N element,the synergistic effect is generated after double doping,which optimizes the chemisorption on the carrier surface.The atomic radius of S was larger than that of N and C,and the doping destroy the original graphite structure of C,causing defects and increasing the number of active sites.The ECSA and MA of Pt₃Cu/NC2-Ts OH catalysts were 134 m² g _Pt^-1,0.41 A mg _Pt^-1,the electron transfer number was 3.99,and the single cell power was 803mW/cm².