Facile route of nitrogen doping in nickel cobalt phosphide for highly efficient hydrogen evolution in both acid and alkaline electrolytes

Abstract

Ternary nickel cobalt phosphide (NiCoP) is believed to be a promising water-splitting electrocatalyst owing to the synergistic effect between different transition metals. Herein, nitrogen doping NiCoP (N-NiCoP) nanowire arrays on carbon fiber paper skeleton (CFP) are synthesized by a facile hydrothermal reaction and subsequent phosphorization-nigtrogenization method. Structural characterizations and density functional theory (DFT) calculations demonstrate that N dopant prefer to replace O defects rather than P atoms in NiCoP lattice. It is illustrated that the Gibbs free energy of H (ΔGH*) in Ni-Co bridge sites is lowered from −0.35 eV of NiCoP to −0.26 eV of N-NiCoP by 25.7%, moreover, the increased d-orbital electronic density of Co and Ni promotes the charge transfer of hydrogen evolution reaction (HER). Consequently, the HER performance of N-NiCoP is substantially enhanced as compared to NiCoP. For N-NiCoP, the overpotentials to reach a current density of 100 mA·cm−2 are 149 and 162.5 mV in 0.5 M H2SO4 and 1 M KOH, respectively, and their Tafel slopes are 40.1 and 59.8 mV·dec−1, respectively. N doping offers an effective and promising route for improved HER performance of NiCoP catalyst in acid and alkaline electrolytes.