A template-free I2-assisted pyrolysis strategy to synthesize coral-like nitrogen-doped carbon with a regulated hierarchical porous structure toward efficient oxygen reduction

Construction of hierarchical porous structures in N-doped carbon (N/C) catalysts is of great significance to promote the reaction kinetics during the electrocatalysis. However, many existing template methods used to synthesize porous carbon networks are usually complicated in operation and might undermine the catalytic active sites of N/C in the post-treatment processes (e.g., templates removal under caustic conditions). Herein, a template-free I2-assisted pyrolysis strategy is developed to regulate the morphology and porous structure of N/C thermally derived from zeolitic imidazolate frameworks. Gas-phase I2 is controllably adsorbed (by adjusting the adsorption temperature) into the porous structure of the zeolitic imidazolate frameworks and then corrodes the frameworks during the pyrolysis. The as-synthesized N/C without any post-treatment features a coral-like morphology, a large pore volume, and a meso/macropore-dominated porous structure, rendering excellent electrocatalytic performance toward oxygen reduction reaction with a half-wave potential of 0.868 V vs. RHE due to the effective exposure of active sites and enhanced mass-transfer capability. A Mg-air battery assembled with the as-synthesized coral-like N/C as the cathode catalyst exhibits an excellent peak power density of 123 mW cm−2 at 0.73 V. This I2-assisted pyrolysis strategy could be widely applicable for regulating the porous structure and morphology of carbon materials derived from different porous precursors for energy conversion and storage applications.