Sponge-templated sandwich-like cobalt-embedded nitrogen-doped carbon polyhedrons/graphene composite as a highly efficient catalyst for Zn-air batteries
Non-noble metal materials are regarded as the most promising catalysts for oxygen reduction reaction (ORR) to overcome the inherent defects of Pt-based catalysts, like high cost, limited availability as well as deficient stability. Here, we fabricate a sandwich-like Co encapsulated in nitrogen doped carbon polyhedrons/graphene (s-Co@NCP/rGO) via a facile and scalable strategy by loading Co-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) layers individually on a polyurethane (PU) sponge template. The 3D sandwich structure is maintained with the assistance of the sponge template, which promotes the uniform dispersion of ZIF-67-derived Co embedded nitrogen doped carbon polyhedrons (Co@NCP) and prevents the graphene plates from agglomerating in time of the annealing process. The final product demonstrates considerable catalytic performance of ORR with a half-wave potential of 0.85 V, a preferable stability and a increased poisoning tolerance by comparison to 20 wt.% Pt/C, which stems from the 3D sandwich-like structure, N/Co-doping effect, large accessible surface area and hierarchical porous structures. The excellent ORR performance of the catalysts means that they can be utilised in a Zn-air battery as cathode catalysts. During such a demonstration, s-Co@NCP/rGO shows a high open-circuit voltage of 1.466 V, a remarkable long-term durability and outstanding peak power density of 186 mV cm-2, which shows its high potential as a prospective alternative for the widespread practical application in the field of non-noble metal ORR catalysts.