Tandem catalysis of Cu/Ni multi-sites promotes oxygen reduction reaction

Cu/Ni多位点串联催化促进氧还原反应

The special electronic characteristics and high atom usage efficiency of metal-nitrogen-carbon(M-N-C)materials have made them extremely attractive for oxygen reduction reactions(ORRs).However,it is inevitable that hydrogen peroxide(H_(2)O_(2))will be formed via the two-electron pathway in ORRs.Herein,the Cu nanoparticles(NPs)have been encapsulated into Ni doped hollow mesoporous carbon spheres(Ni-HMCS)to reduce the generation of H_(2)O_(2)in ORR.Electrochemical tests confirm that the introduction of Cu NPs improves the ORR performance greatly.The obtained Cu/Ni-HMCS exhibits a half-wave potential of 0.82 V vs.reversible hydrogen electrode and a limited current density of 5.5 mA cm^(-2),which is comparable with the commercial Pt/C.Moreover,Cu/Ni-HMCS has been used in Zn-air battery,demonstrating a high power density of 161 mW cm^(-2)and a long-term recharge capability(50 h at 5 mA cm^(-2)).The theoretical calculation proposes a tandem catalysis pathway for Cu/Ni multi-sites catalysis,that is,H_(2)O_(2)released from the Ni-N_(4)and Cu-N_(4)sites migrates to the Cu(111)face,on which the captive H_(2)O_(2)is further reduced to H_(2)O.This work demonstrates an interesting tandem catalytic pathway of dual-metal multi-sites for ORR,which provides an insight into the development of effective fuel cell electrocatalysts.

金属-氮-碳(M-N-C)材料的特殊电子性质和较高的原子利用率,在氧还原反应(ORR)中得到广泛研究.然而,在氧还原过程中,形成过氧化氢(H_(2)O_(2))的双电子途径是无法避免的.本文设计通过将Cu纳米粒子(NPs)引入到中空介孔碳球(HMCS)中来降低M-N-C材料的双电子选择性,增强其ORR性能.电化学测试证实了Cu NPs对ORR性能的改善.相对于可逆氢电极,Cu/Ni HMCS具有0.82 V的半波电位和5.5 mA cm^(-2)的极限电流密度,与商业Pt/C相当.此外,将Cu/Ni-HMCS应用在锌-空气电池中,表现出161 mW cm^(-2)的高功率密度和长期充放电稳定性(在5 mA cm^(-2)条件下持续50小时).理论计算提出了Cu/Ni多位点催化串联催化途径,即O_(2)在Ni-N_(4)和Cu-N_(4)位点还原生成的H_(2)O_(2)迁移到Cu(111)晶面,在Cu(111)面进一步还原为H_(2)O.本研究展示了ORR双金属多位点串联催化途径,为燃料电池电催化剂的设计提供了新思路.