Strategies For Controlling The Activity And Stability Of Pt-Ni Alloy Catalysts For Oxygen Reduction

Proton exchange membrane fuel cells（PEMFCs）could operate at low temperature and with high energy conversion efficiency.While,the cathode catalyst is several times more than that of anode,thus becames a key factor affecting the cost of PEMFCs.Currently,the commercial catalysts are mostly 3-5 nm Pt-based alloys,but their expensiveness and unsatisfactory catalytic performance hinder their commerciallization.Because the overflow of base metals in an acidic environment leads to the disappearance of alloying;the migration and maturation of nanoparticles cause agglomeration;the corrosion of the carbon carrier under high potential causes the shedding of nanoparticles.Thus,it is significant to investigate the relationship between composition,structure and activity of oxygen reduction catalysts.The main contents of this work are as follows:（1）The introduction of acid-resistant W stabilizes the low-coordination Pt atoms on the surface of the catalyst,thereby reducing the Ni content on the surface,and inhibiting the dissolution of Ni in the alloy.In addition,the W atoms mostly exist on the surface of the catalyst in the form of coordination unsaturated WO_x,which is conducive to the overflow of OH*on the surface of the Pt atoms and improves the catalytic efficiency.At the same time,the Pt content in the catalyst is optimized to balance the catalytic activity and stability.Among them,Pt₃Ni₃WN/C exhibits excellent catalytic activity and stability.The initial mass activity in 0.1 M HCl O₄ is 400 m A mg^-1Pt,after 30k CV cycles,the activity decline is only 48%,compared with 61%of commercial Pt/C.This work is helpful to understand the effect of doping on the activity and stability of Pt Ni system.（2）During the electrochemical process,the stability of nanoparticles is inevitably reduced by the aggregation of nanoparticles and the corrosion of carriers.In this study,the Pt Ni-Mo O_x/C catalyst is prepared by pyrolysis and ethylene glycol method.The results show that the strong interaction between metals in Pt Ni-Mo O_x/C contributes to the stability of Pt Ni nanoparticles and inhibits their migration.The composite of metal oxide and carbon support alleviates the nanoparticle shedding caused by carrier corrosion.Furthermore,the spillover effect between Pt and Mo O_xcan effectively promote the spillover of oxygen-containing protons on the surface of Pt atoms and improve the reaction efficiency.The above results show that the strong interaction between metals is an effective way to improve the catalytic performance of Pt Ni alloy.（3）Metal oxides have been developed as a new type of catalyst carrier for fuel cells due to their strong electrochemical stability.However,the low electron transfer efficiency of oxides seriously hinders the interaction between electrons and ions in the ORR process.It is found that coordination unsaturated metal oxides have positive effects on improving charge transfer and promoting the ORR reaction.In this study,a series of metal oxide anchored Pt Ni alloys were synthesized to reveal the relationship between their catalytic performance and the content of coordination unsaturated WO_x.The results show that the catalytic activity is positively correlated with WO_x content.However,WO_x is easily oxidized in an acidic environment,so the stability of WO_x shows a negative correlation.Therefore,it is necessary to further adjust the content of WO_x to balance the catalytic activity and stability.This study reveals the effect of coordination unsaturated WO_x on the catalytic performance and provides a promising strategy for the design of efficient and stable ORR catalysts.