Iron-doped nickel sulfide@phosphate heterostructure nanosheets constructed from solvothermal P2S5 and layered double hydroxides for electrocatalytic oxygen evolution†

The design of efficient and active electrocatalysts for the oxygen evolution reaction (OER) is crucial for hydrogen generation from water electrolysis. Here, crystalline iron-doped nickel sulfide core-amorphous iron-doped nickel phosphate shell heterostructured nanosheets grown on nickel foam (Ni_0.9Fe_0.1S@NiFe(PO₄)_x/NF) are prepared by a solvothermal reaction of nickel iron layered double hydroxides on NF (NiFe-LDH/NF) with P₂S₅. The heterogeneous interface induces the electronic interaction between the Ni_0.9Fe_0.1S and NiFe(PO₄)_x phases, which is beneficial for the OER. The electrode exhibits excellent OER performance, requiring only 208 mV and 246 mV at current densities of 10 mA cm⁻² and 100 mA cm⁻², respectively, and a low Tafel slope of 38.75 mV dec⁻¹ in 1 M KOH. The OER mechanistic pathways of both Ni_0.9Fe_0.1S@NiFe(PO₄)_x/NF and NiFe-LDH/NF involve decoupled electron and proton transfer processes. The increase in the acidity of Ni sites leads to the enhanced participation of LOM for Ni_0.9Fe_0.1S@NiFe(PO₄)_x/NF. Additionally, the electrode also shows long-term durability (150 h), with the conversion of surface metal sulfides and phosphates to hydroxides and (oxy)hydroxides.