Fabrication of Multicavity Hierarchically Porous Carbon Nanospheres Using Compressed CO2 for Overall Water Splitting

Abstract The rational design of efficient bifunctional electrocatalysts is crucial for overall water splitting. As a catalyst support, the multicavity hierarchically porous carbon spheres scaffold facilitates efficient electron transport and structural stability during catalysis. Herein, we report a reverse microemulsion strategy assisted by supercritical/compressed CO2 for the synthesis of multicavity hierarchically porous carbon nanospheres. Pyrolysis of nickel phthalocyanine (NiPc) and dicyandiamide as nickel and nitrogen sources, respectively, yields nickel nanoparticles embedded in nitrogen-doped porous carbon nanospheres modified with atomically dispersed Ni sites (Ni–N@MC). The multicavity hierarchically porous structure affords abundant active sites and an enlarged interface, exhibiting low overpotentials of 197 mV for the oxygen evolution reaction (OER) and 148 mV for the hydrogen evolution reaction (HER) at 10 mA cm–2, thus demonstrating excellent bifunctional electrocatalytic activity. An overall water-splitting electrolyzer using this catalyst as both electrodes achieves 10 mA cm–2 at 1.59 V with over 24 h stability.