Homologous NiO//Ni2P nanoarrays grown on nickel foams: a well matched electrode pair with high stability in overall water splitting

Homologous NiO, Ni₃S₂, and Ni₂P nanoarrays were obtained by thermolysis, sulfuration, and phosphorization of the Ni(SO₄)_0.3OH_1.4 belt-like precursors. The three types of porous nickel compound films grown on nickel foam with a thickness of ∼8 μm have been used as anodes and cathodes in a two-electrode setup for overall water splitting. The electrode pairing of Ni_xM_y//Ni_xM_y (M = O, S, and P) for electrocatalysis in order of superiority is as follows: NiO//Ni₂P > Ni₃S₂//Ni₂P > Ni₂P//Ni₂P > Ni₃S₂//Ni₃S₂ > NiO//Ni₃S₂ > NiO//NiO. The other two sets of Ni_xM_y with different thicknesses of ∼5 and ∼11 μm also follow the abovementioned order. The well matched electrode pair of NiO_OER//Ni₂P_HER only needs 1.65 V, whereas NiO//NiO pair needs 1.84 V to afford the current of 10 mA cm^-2 in 1 mol L^-1 of aqueous KOH solution. In particular, the current density retention of the NiO//Ni₂P reached 92% after 120 hours of electrolysis at 1.70 V (NiO//NiO only maintains 72% after 30-hour electrolysis). The novelty of this study focuses on fabricating a well matched electrode pair to substantially enhance its electrochemical performance and durability, which would provide a new insight into developing non-noble, highly efficient, and stable electrode pairs.