Optimizing oxygen redox kinetics of M-N-C electrocatalysts via an in-situ self-sacrifice template etching strategy

The accessibility and mass transfer between catalytic sites and substrates/intermediates are essential to a catalyst's overall performance in oxygen electrocatalysis based energy devices. Here, we present an “in-situ self-sacrifice template etching strategy” for reconstructing MOF-derived M-N-C catalysts, which introduces micro‑meso-macro pores with continuous apertures in a wide range and a central hollow-out structure to optimize the electrochemical oxygen redox kinetics. It is realized via one-step pyrolysis of ZIF-8 single crystal epitaxially coating on a multi-functional template of the Fe, Co co-loaded mesoporous ZnO sphere. The ZnO core is reduced during the general pyrolysis of ZIF-8 into M-N-C and acts as a pore former to etch the surrounding ZIF-8 shell into diverse channels anchoring highly exposed Fe and Co-based active sites with edge enrichment. The redesigned catalyst reveals apparent structural benefits towards enhanced oxygen redox kinetics as bifunctional cathode catalysts of rechargeable zinc-air battery compared with the primitive bulk M-N-C catalysts and the mixture of commercial Pt/C and Ir/C. The unique structure-based activity advantages, the omitted template removal step and good template compatibility during synthesis make the strategy universal for the channel engineering of electrocatalysts.