Direct Electrodeposition of Phosphorus-Doped Nickel Superstructures from Choline Chloride–Ethylene Glycol Deep Eutectic Solvent for Enhanced Hydrogen Evolution Catalysis

Abstract

Hydrogen produced by electrochemical water splitting offers a hopeful and renewable solution to address the global energy crisis; however, development of highly efficient hydrogen generation electrocatalysts remains a big challenge. Herein, self-supported P-doped nickel superstructure films (NiPx) developed on Cu foil were prepared via a facile one-step electrodeposition route from the choline chloride–ethylene glycol (Ethaline)-based deep eutectic solvent (DES). Two depositional patterns including potentiostatic deposition and a consecutive potential cycling approach were compared, and the latter model with a potentiodynamic control was found to be a valid electrochemical protocol to create crack-free NiPx films which were highly active for catalyzing hydrogen evolution reaction (HER) under an alkaline condition. The optimal deposited sample with a Ni/P ratio of 1:0.056 achieved a low overpotential of 105 mV to deliver a current density of 10 mA cm–2 with a small Tafel slope of 44.7 mV dec–1 and excellent catalytic stability for at least 60 h. Detailed experimental investigations coupled with theoretical analyses revealed that the high-performance catalytic activity of the NiPx films originated from the enriched active sites and enhanced electronic conductivity induced by P-doping, which also altered the surface electronic structure of the material and resulted in a lower energy barrier for water dissociation and favorable H adsorption free energy. This study provides a new electrochemical potentiodynamic strategy performed in DES for the fabrication of transition-metal-phosphide-based catalysts for enhancing HER catalysis.