Tuning the dual-active sites of ZIF-67 derived porous nanomaterials for boosting oxygen catalysis and rechargeable Zn-air batteries

The rational control of the active site of metal-organic frameworks (MOFs) derived nanomaterials is essential to build efficient bifunctional oxygen reduction/evolution reaction (ORR/OER) catalysts. Accordingly, through designing and constructing a Co₃O₄-Co heterostructure embedded in Co, N co-doped carbon polyhedra derived (Co₃O₄-Co@NC) from the in-situ compositions of ZIF-67 and cobalt nanocrystals synthesized by the strategy of in-situ NaBH₄ reduction, the dual-active site (Co₃O₄-Co and Co-N_x) is synchronously realized in a MOFs derived nanomaterials. The formed Co₃O₄-Co@NC shows excellent bifunctional electrocatalytic activity with ultra-small potential gap (ΔE = E_j=10 (OER) - E_1/2 (ORR)) of 0.72 V, which surpasses the commercial Pt/C and RuO₂ catalysts. The theory calculation results reveal that the excellent bifunctional electrocatalytic activity can be attributed to the charge redistribution of Co of Co-N_x induced by the synergistic effects of well-tuned active sites of Co₃O₄-Co nanoparticle and Co-N_x, thus optimizing the rate-determining step of the desorption of O₂* intermediate in ORR and OH* intermediate in OER. The rechargeable Zn-air batteries with our bifunctional catalysts exhibit superior performance as well as high cycling stability. This simple-effective optimization strategy offers prospects for tuning the active site of MOF derived bifunctional catalyst in electrochemical energy devices.