Efficient water splitting catalyzed by flexible NiP₂ nanosheet array electrodes under both neutral and alkaline solutions

Designing a non-noble-metal catalyst with high efficiency toward oxygen evolution reactions (OERs) is critical for renewable energy storage and conversion devices (e.g., water-splitting and metal-air batteries). In the current study, a flexible electrode of nickel diphosphide nanosheet arrays on carbon cloth (NiP₂/CC) is synthesized through phosphidation of Ni(OH)₂ nanosheet arrays as a precursor on the carbon cloth. The resultant three-dimensional (3D) porous nanosheet array architecture enhances the exposure of surface active sites and the release of gaseous products. When used as an OER catalyst, such an integrated 3D array electrode affords a current density of 4 mA cm⁻² at an OER overpotential of 570 mV with good stability in neutral solution. Moreover, the NiP₂/CC electrode also exhibits good OER performance (j = 20 mA cm⁻² at η = 310 mV) under alkaline conditions. Notably, this electrode also shows high activity and stability under both neutral and alkaline media toward the HER. More importantly, when assembled as a symmetric full water splitting device with NiP₂/CC as both the cathode and anode, a current density of 10 mA cm⁻² at a voltage of 1.65 V is achieved in 1.0 M KOH solution. Owing to its low cost and high activity, NiP₂/CC presents potential applications toward overall water splitting electrolysis and other electrochemical devices.