P-doped nickel sulfide nanosheet arrays for alkaline overall water splitting

Abstract

Heazlewoodite, Ni₃S₂, is one of the most promising bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media due to its metallic conductivity and low cost. However, the reported HER activity of Ni₃S₂ is still unsatisfactory. Herein, 3D self-supported phosphorus-doped Ni₃S₂ nanosheet arrays on Ni foam (P-Ni₃S₂/NF) are synthesized by a simple one-step simultaneous phosphorization and sulfuration route and exhibit dramatically enhanced HER and OER activity. The introduction of P anions significantly optimized the hydrogen adsorption free energy (ΔG_H*) and increased the electrochemical surface area (ECSA). Accordingly, the optimal P-Ni₃S₂/NF exhibits relatively low overpotentials of 101 mV and 256 mV to drive a current density of 10 mA cm⁻² for the HER and OER in 1 M KOH. The reported electrocatalyst activation approach by anion doping can be adapted for other transition metal chalcogenides for overall water splitting, offering great promise for future applications.