▎ 摘　　要

Developing low-cost, high-performance electrocatalysts for the oxygen reduction reaction (ORR) is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative polymerization. Then iron (Fe) salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FeN0.05 nanoparticles after pyrolysis, generating ORR active sandwich-like carbon nanosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential similar to 30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only similar to 40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon nanosheets hold great potential as alternatives to precious metalbased catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.