N-doped carbon-coupled nickel nitride species/Ni2P heterostructure for enhancing electrochemical overall water splitting performance

Abstract

A class of electrodes consisting of amorphous-crystalline nickel nitride species (NNS)/Ni2P heterostructures anchored on N-doped carbon (NC) in-situ grown on Ni foam (NF) are reported (NNS/Ni2P@NC-NF). Thanks to the optimized electronic structure, d-band center and the existence of defective N-doped carbon regulated by the construction of heterostructure and the use of different N sources, the optimal NNS-d/Ni2P@NC-NF electrode exhibits excellent hydrogen evolution reaction (HER) activity and oxygen evolution reaction (OER) activity in alkaline electrolyte, which shows low overpotentials of 47 mV for HER and 210 mV for OER, respectively, attaining a current density of 10 mA·cm−2. Significantly, with NNS-d/Ni2P@NC-NF as both the anode and cathode for overall water splitting, they deliver a current density of 10 mA·cm−2 at a low cell voltage of ≈ 1.49 V. Moreover, the NNS-d/Ni2P@NC-NF electrode has excellent long-term durability for at least 120 h at the current density of 10 mA·cm−2. Density-functional theory (DFT) calculation also demonstrates that the construction of the heterostructure can effectively optimize the electronic structure and d-band center of the catalysts, thereby decreasing the Gibbs free energies of the rate-determining step and boosting the catalytic activity.