S-vacancies and iron-doped nickel sulfide nanosheets constructed by a solvothermal method as efficient catalysts for electrocatalytic oxygen evolution

The development of high-performance and stable electrocatalysts for oxygen evolution reaction (OER) is essential to improve the overall efficiency of water splitting. Here, S-vacancies and iron-doped nickel sulfide nanosheets (V_s-Ni₂Fe₁S₂/NF) were successfully prepared on the surface of nickel foam via solvothermal reaction of nickel–iron layered double hydroxide with sublimed sulfur added with sodium borohydride. Under the synergistic regulation of iron-doped and S-vacancies, V_s-Ni₂Fe₁S₂/NF shows excellent electrocatalytic performance and long-term durability. To reach current densities of 10 and 500 mA cm⁻², V_s-Ni₂Fe₁S₂/NF requires only 185 (±5) and 248 (±5) mV overpotential, respectively, and can maintain long stability for 350 h at 500 mA cm⁻². The change of the mechanical pathway from adsorbate evolution mechanism to lattice oxygen oxidation mechanism is due to the increased acidity of the Ni site in V_s-Ni₂Fe₁S₂/NF, which facilitates the decouped proton and electron transfer process. Density functional calculation results show that the introduction of Fe atoms and S vacancies in Ni₃S₂ can enhance the conductivity of the intermediates by regulating the electronic structure of the intermediates, optimize the adsorption or desorption energy, and thus significantly improve the OER activity. For V_s-Ni₂Fe₁S₂/NF (+, −) cell, a voltage of 1.56 V is required to achieve 10 mA cm⁻². In addition, V_s-Ni₂Fe₁S₂/NF catalyst also showed low overpotential (270 mV at 100 mA cm⁻²) and high alkaline tolerance (100 h at 100 mA cm⁻²) at 30 wt% KOH of 70 °C. This shows that it has potential industrial application.