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Although PtNi catalyst possesses good oxygen reduction activity,its poor stability is the main obstacle for the commercialization of proton exchange membrane fuel cells(PEMFCs).In this work,we introduce the acid-resistant refractory Mo to enhance the structure stability and modify the electronic structure of Pt in the prepared PtNi catalyst,improving the catalytic activity for oxygen reduction reaction(ORR).In addition,near-surface Pt content in the nanoparticle is also optimized to balance the ORR activity and stability.The electrochemical results show that the alloy formed by Mo and PtNi is obviously more stable than the PtNi alloy alone,because the acid-resistant Mo and its oxides effectively prevent the dissolution of Pt.Especially,the Pt3Ni3MoN/C exhibits the optimal ORR catalytic performance in O2-saturated 0.1 mol L-1 HClO4 aqueous solutions,with mass activity(MA)of 900 mA mg-1Pt at 0.90 V vs.RHE,which is 3.75 times enhancement compared with the commercial Pt/C(240 mA mg-1Pt).After 30k accelerated durability tests,its MA(690 mA mg-1Pt)is still 2.88 times higher than the pristine Pt/C.This study thus provides a valuable method to design stable ORR catalysts with high efficiency and has great significance for the commercialization of PEMFCs.