Built-in electric field engineering in Co2N0.67/CoP heterostructures for glycerol electrooxidation-assisted hydrogen production

Glycerol electrooxidation emerges as an electrochemically cogent paradigm to supplant the sluggish oxygen evolution reaction in water electrolysis. However, most non-precious catalysts still suffer from large electrolytic voltage and poor stability when operating at industrially relevant current densities. Here, we develop a heterostructure catalyst by immobilizing abundant cobalt phosphide (CoP) nanoparticles on conductive cobalt nitride (Co₂N_0.67) support, which results in the construction of a strong built-in electric field at the heterointerface. The optimal catalyst demonstrates effective bifunctional catalytic performance, yielding an industrial-level current density of 500 mA cm^-2 at low potentials of -141 mV and 1.44 V for hydrogen evolution and glycerol oxidation, respectively. When integrated into a flow cell system, this catalyst maintains good stability for 260 hours at 1 A cm^-2 (1.67 V) while preserving > 85% Faradaic efficiency for formate production. Both theoretical and experimental analyses substantiate that the built-in electric field drives directional electron transfer from CoP to Co₂N_0.67, forming an electron-deficient region at the CoP interface that enriches OH* species, and an electron-rich region at the Co₂N_0.67 interface, facilitating hydrogen adsorption, thereby expediting the glycerol and H* co-adsorption process. Multiple in-situ spectroscopic characterizations verify the existence of a combined direct/indirect oxidation mechanism for glycerol electrooxidation. This discovery sets the stage for low-voltage hydrogen production by hybrid water splitting using the excess electrical power whenever and wherever available.