Synthesis And Properties Of Platinum Alloy Fuel Cell Catalysts

Hydrogen energy has the advantages of high energy capacity and environmental friendliness,and is considered as a potential energy carrier in many energy schemes with low greenhouse gas（GHG）emissions.Hydrogen fuel cell is a kind of pollution-free driving power that converts hydrogen energy directly into electric energy,which is expected to solve the problem of polluting gas emission in transportation industry.At present,proton exchange membrane fuel cells（PEMFCs）technology is in a period of rapid development.The high cost,low activity and limited performance durability of cathode oxygen reduction reaction（ORR）catalyst are the main problems.How to reduce the amount of platinum in the catalyst and improve the activity and durability of the catalyst is particularly important.In order to reduce the platinum load of ORR catalyst and improve its activity and stability,this paper carried out research on platinum-nickel alloy catalyst,explored its synthesis method,and further optimized its catalytic activity through three strategies,such as pickling calcination treatment,doping with a third metal and doping with anionic nitrogen,the activity and stability of platinum-based alloy ORR catalyst were improved,and good performance was obtained by fuel cell test.The details are as follows:1.PtNi/C alloy catalyst was synthesized by solvent method,and its ORR activity was investigated.The specific activity was 2.66mA cm^-2,and the mass activity was 1.55A mg_Pt^-1,showing better performance than commercial Pt/C.These results indicate that alloying can effectively improve the ORR performance of platinum-based catalysts.The specific activity of catalysts under N₂ and H₂ calcination atmosphere reached 3.3mA cm^-2 and 3.63 mA cm^-2,respectively,which further improved its specific activity.The increase of the specific activity is attributed to the increase of the size of the nanoparticles after calcination,the surface structure recombination,and the exposure of more Pt active sites.The PtNi/C catalyst was prepared as membrane electrode assemblies by spraying process.The peak power density was 1.82W cm^-2 and the current density was 2.16A cm^-2 at 0.65V（H₂/O₂）.After 100h of durability testing,the voltage dropped from the initial 0.7V to 0.688V,decreasing by less than 2%.The PtNi/C catalyst was prepared as membrane electrode assemblies by scraping and printing process.The peak power density was 2.16W cm^-2,and the current density at 0.65V was 2.20A cm^-2（H₂/O₂）.The performance of the membrane electrode assemblies was further improved by optimizing the preparation process.2.The influence of the addition of the third metal element on the performance of PtNi/C catalyst was explored.A series of M-PtNi（M=Mn,Fe,Mo,Pb,Pd,Cr,Cu,Ru,Co）ternary platinum alloy catalysts were synthesized,and it was found that Mo can effectively improve the stability of the catalysts.In the RDE test,its specific activity was 1.53mA cm^-2,and its mass activity was0.77A mg_Pt^-1.After 4000 cycles durability test,the half-wave potential was only1mv offset,and the specific activity and mass activity did not decrease and only decreased by 4%compared with the initial specific activity and mass activity.In the single cell test,its peak power density is 2.26W cm^-2 and current density is2.29A cm^-2 at 0.65V（H₂/O₂）,which also shows good performance.3.The influence of anionic nitrogen doping on the performance of PtNi/C catalyst was studied.By exploring the effects of different nitrogen sources on its performance,dicyandiamide was found to be the best nitrogen source and the optimal nitrogen mixing parameters were explored.The specific activity of the prepared N₁-PtNi/C catalyst reached 3.68mA cm^-2,1.4 times that of PtNi/C catalyst and 13 times that of commercial Pt/C catalyst.The mass activity reached2.89 A mg_Pt^-1,1.9 times that of PtNi/C catalyst and 12 times that of commercial Pt/C catalyst.This improvement was due to the formation of N_X-Ni site,N regulates the electronic structure of PtNi site,thus enhancing ORR activity.