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

Abstract

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.