Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting

TLDR

Efficient water splitting demands highly active, earth‑abundant, and robust catalysts, and while monometallic phosphides such as Ni₂P are active, theory suggests that substituting extrinsic metals could further enhance performance, though this has been little explored. The study introduces a novel PH₃ plasma‑assisted method to convert NiCo hydroxides into ternary NiCoP, offering a versatile route to synthesize diverse bimetallic or complex phosphides. The authors employ PH₃ plasma to transform NiCo hydroxides into NiCoP nanostructures on Ni foam, enabling scalable synthesis of complex phosphides. The resulting NiCoP nanostructure on Ni foam delivers exceptional HER (32 mV overpotential at –10 mA cm⁻²) and OER (10 mA cm⁻² at 280 mV) performance, enabling overall water splitting at 10 mA cm⁻² with a 1.58 V cell voltage—among the best for non‑noble metal catalysts.

Abstract

Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH3 plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at −10 mA cm–2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm–2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm–2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications.