P‑Doped\nIron–Nickel Sulfide Nanosheet\nArrays for Highly Efficient Overall Water Splitting

Abstract

Iron–nickel\nsulfide ((Ni,Fe)₃S₂) is\none of the most promising bifunctional electrocatalysts for both the\nhydrogen evolution reaction (HER) and oxygen evolution reaction (OER)\nin alkaline media because of their metallic conductivity and low cost.\nHowever, the reported HER activity of (Ni,Fe)₃S₂ is still unsatisfactory. Herein, three-dimensional self-supported\nphosphorus-doped (Ni,Fe)₃S₂ nanosheet arrays\non Ni foam (P-(Ni,Fe)₃S₂/NF) are synthesized\nby a simple one-step simultaneous phosphorization and sulfuration\nroute, which exhibits dramatically enhanced HER activity as well as\ndrives remarkable OER activity. The incorporation of P significantly\noptimized the hydrogen/water absorption free energy (Δ<i>G</i>_H*/Δ<i>G</i>_H₂O*), enhanced electrical conductivity, and increased electrochemical\nsurface area. Accordingly, the optimal P-(Ni,Fe)₃S₂/NF exhibits relatively low overpotentials of 98 and 196 mV\nat 10 mA cm^–2 for HER and OER in 1 M KOH, respectively.\nFurthermore, an alkaline electrolyzer comprising the P-(Ni,Fe)₃S₂/NF electrodes needs a very low cell voltage\nof 1.54 V at 10 mA cm^–2 and exhibits long-term stability\nand outperforms most other state-of-the-art electrocatalysts. The\nreported electrocatalyst activation approach by anion doping can be\nadapted for other transition-metal chalcogenides for water electrolysis,\noffering great promise for future applications.