Conceptual design of three-dimensional CoN/Ni3N-coupled nanograsses integrated on N-doped carbon to serve as efficient and robust water splitting electrocatalysts

Abstract

Developing binder-free, low-cost, and efficient electrocatalysts for water splitting is very important to meet the ever-increasing global energy demands. We have judiciously designed a polyaniline (PANI)-mediated protocol for the synthesis of nickel–cobalt nitride (NCN) heterostructures on carbon cloth (CC) to be applied as catalysts for full electrochemical splitting of water. Controlled pyrolyzation of the nickel–cobalt precursor on PANI-coated CC generates assembled grass-like nanostructures of cobalt nitride (CoN) and nickel nitride (Ni₃N) along with beneficial, conductive nitrogen-doped carbon layers on CC for improved electrochemical activity. The generation of numerous catalytically active centers with expeditious charge and mass transportation due to the incorporated nickel and high mechanical stability owing to the self-supporting nature of the designed material result in excellent and stable electrocatalytic performance. The designed NCN/CC electrode requires low overpotentials (η₁₀) of 247 and 68 mV to attain a current density of 10 mA cm⁻² during oxygen evolution and hydrogen evolution reactions, respectively, with appreciable stability (>90% retention of the initial current density) over a 24 h long electrochemical test in 1.0 M KOH. Finally, the NCN/CC electrocatalyst is utilized to demonstrate full alkaline water splitting at a cell voltage of 1.56 V to deliver the current density of 10 mA cm⁻² with tremendous stability over 240 h. Moreover, NCN/CC could afford a stable current density of 10 mA cm⁻² towards full water splitting at 1.59 V cell voltage in acidic electrolyte with 100 h long-term stability. These results suggest its prospects as a substitute for expensive noble-metal-based water splitting electrocatalysts in practical applications.