d-band center upshift and electronic modulation of nickel cobalt phosphide integrated with reduced graphene oxide for stable and efficient water-splitting electrocatalysis

Green hydrogen is crucial for advancing renewable energy technologies and protecting the environment. This study introduces a controllable method for bimetallic nickel–cobalt phosphide on reduced graphene oxide on nickel foam (NiCo₃P.C/NF). The material demonstrated low overpotentials of 58 and 180 mV at 10 mA cm⁻² for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH. It achieved excellent electrochemical water-splitting performance with operating voltages of 1.54 and 2.6 V at 10 and 500 mA cm⁻², respectively. The overall water-splitting performance of NiCo₃.C/NF was extremely stable after 75 h of operation at 53 mA cm⁻², retaining 98% efficiency, better than the sample Pt–C + RuO₂, and outperforming previous reports. Density functional theory (DFT) results revealed a synergistic NiCo₃P.C interaction that yields nearly zero Gibbs free energy change (−0.100 eV) and upshift d-band center, the real active site at the Ni in HER, and the lowest overpotentials 0.26 V at the P active sites for OER. Furthermore, electronic charge distribution shows the maximum charge distribution between the NiCo₃P phase and graphene sheet heterojunction, enhancing the electrocatalyst conductivity. This combined approach offers an innovative strategy to design sustainable electrocatalysts for water splitting.