Solvothermally synthesized graphene nanosheets supporting spinel NiFe₂O₄ nanoparticles as an efficient electrocatalyst for the oxygen reduction reaction

The production of efficient and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is one of the key issues for the extensive commercialization of fuel cells. In this paper, we describe a facile one-pot hydrothermal synthesis route to in situ grow spinel NiFe₂O₄ nanoparticles onto the graphene nanosheets which were produced in advance by a scalable solvothermal reduction of chloromethane and metallic potassium. The resultant NiFe₂O₄/graphene nanohybrid exhibits superior electrocatalytic activity for the ORR to pure graphene nanosheets and unsupported NiFe₂O₄ nanoparticles, which mainly favours a desirable direct 4e^- reaction pathway during the ORR process. Meanwhile, the NiFe₂O₄/graphene nanohybrid exhibits the outstanding long-term stability for the ORR, outperforming the commercial 20 wt% Pt/C based on the current-time chronoamperometric test. The excellent catalytic activity and stability of NiFe₂O₄/graphene nanohybrid are ascribed to the strong coupling and synergistic effect between NiFe₂O₄ nanoparticles and graphene nanosheets.