Nitriding-reduction fabrication of coralloid CoN/Ni/NiO for efficient electrocatalytic overall water splitting

The introduction of nitride in Ni/NiO-based catalytic system for electrocatalystic water splitting via a skillful strategy remains a great challenge. Herein, we proposed a one-step urea nitriding-reduction strategy for the fabrication of novel CoN/Ni/NiO electrocatalyst on carbon cloth (CC). The combination of CoN and Ni/NiO could construct CoN/Ni interface and expose more active sites, thus exhibiting excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in alkaline media. Consequently, CoN/Ni/NiO catalyst exhibited remarkable HER/OER performance with an overpotential of 92 mV/114 mV at 10 mA cm^-2 in 1.0 M KOH, along with a low cell voltage of 1.56 V to enhance overall water splitting. In addition, when CoN was introduced in Ni/NiO system, CoN/Ni/NiO displayed high conductivity, large active surface areas, high Faradic efficiency (FE) and remarkable stability. Density functional theory (DFT) calculations demonstrated that CoN/Ni/NiO possessed a decreased d-band center beneficial for optimizing the energy barrier of intermediates. Specifically, the ΔG_H2O (0.088 eV) and ΔG_H* (0.18 eV) in HER and the ΔG_OOH* (1.4 eV) of rate determining step (O*→OOH*) in OER of CoN/Ni/NiO catalyst were optimized to achieve high water splitting activity. Simultaneously, for adsorbed H₂O on CoN/Ni/NiO, the OH bond length extended from 0.975 to 1.110 Å, and the bond angle enlarged from 104.271 to 109.471°, thereby directly demonstrating the excellent HER/OER performance of CoN/Ni/NiO.