Developing renewable and clean energy systems for overall water electrolysis requires low-cost, highly efficient, and stable catalysts. With this motivation, nickel cobalt phosphorus (NiCoP) was electrodeposited onto nickel foam (NF) and then modified with graphitic carbon nitride (g-C₃N₄). The designed g-C₃N₄/NiCoP/NF electrode was used for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline water electrolysis. It exhibited a small overpotential of 80 mV@10 mA cm⁻² with a Tafel slope of 89 mV dec⁻¹ for the HER. It also exhibited an overpotential of 370 mV@10 mA cm⁻² with a Tafel slope of 64 mV dec⁻¹ for the OER. The g-C₃N₄/NiCoP catalyst exhibited satisfactory stability in an alkaline electrolyzer system, in which g-C₃N₄/NiCoP/NF was used as the anode and cathode. Meanwhile, the electrocatalyst requires only a cell voltage of 1.70 V to achieve 10 mA cm⁻² current density for overall water electrolysis.