Metal-organic framework assembly derived hierarchically ordered porous carbon for oxygen reduction in both alkaline and acidic media

Efficient electrocatalysts for oxygen reduction reaction (ORR) are desirable but challenge in harsh conditions, which seriously limits the widespread application of many clean energy devices. Herein, a series of zeolitic imidazolate framework-8 (ZIF-8) assemblies are fabricated using a freestanding template and further used as pyrolytic precursors for synthesizing metal-free ORR catalysts. Impressively, the optimized 3D porous nitrogen-doped carbon (PNC-30) exhibits a half-wave potential of 0.90 and 0.76 V in alkaline and acidic electrolytes, respectively. Furthermore, when used as the cathode in zinc-air batteries, PNC-30 reaches a power density of 150 mW cm−2, 1.6 times higher than the commercial Pt/C. And, the PEMFCs equipped with PNC-30 cathode deliver a high power density of 562 W g−1. Experimental results and computational analysis indicate that the outstanding ORR performance is ascribed to the unique trimodal-porous structure, where micropores give abundant active sites/defects and meso-/macropores provide rapid mass transfer capabilities.