Ultralow-overpotential non-noble metal oxide–doped g-C3N4 heterostructure for efficient bifunctional water splitting electrocatalyst across all pH conditions

Creating affordable and efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) across different pH levels remains a significant challenge in renewable energy research. In this study, we report a novel hierarchical nanocomposite comprising CeO₂ and NiO nanospheres integrated with g-C₃N₄ nanosheets on nickel foam (NF), demonstrating bifunctional electrocatalytic activity toward HER and OER across alkaline, acidic, and neutral media. The g-C₃N₄/CeO₂/NiO exhibits ultra-low overpotentials (0.064 V for HER and 0.281 V for OER at 50 mA/cm²) and excellent durability. The synergistic electron transfer between Ce³⁺/Ce⁴⁺and Ni²⁺ in the porous g-C₃N₄ matrix reduces intermediate binding energies and boosts electrocatalytic kinetics. A two-electrode electrolyzer assembled with this hybrid catalyst achieves efficient overall water splitting at low cell voltages of 1.72 V (alkaline), 1.92 V (acidic), and 1.98 V (neutral) at 200 mA/cm². The superior performance is attributed to strong interfacial electron interactions among Ni²⁺, Ce³⁺/Ce⁴⁺, and the g-C₃N₄ matrix, which optimize intermediate binding energies and accelerate reaction kinetics. These results highlight the g-C₃N₄/CeO₂/NiO composite as a promising and versatile electrocatalyst for pH-universal water splitting.