Nickel encapsulated in carbon-dot-derived nanosheets for efficient hydrogen evolution via urea-assisted water electrolysis

Abstract

The hydrogen evolution reaction (HER) through the urea-assisted electrolysis of water possesses considerable potential to reduce the consumption of energy during hydrogen generation. As a more favorable active site for the urea oxidation reaction (UOR), Ni has the merits of high intrinsic activity, excellent conductivity, and low price. However, achieving the desired activity and stability for single metal Ni remains a great challenge. Selecting appropriate substrates to maximize the activity of Ni while also maintaining its stability may be a feasible strategy. Herein, using N-doped carbon dots (NCDs) as a participant, a hydrophilic electrocatalyst with Ni nanoparticles wrapped in a carbon-dot-derived coating (Ni@NCDs) was fabricated. Benefiting from the encapsulated structure and their benign hydrophilicity, the Ni@NCDs showed an excellent bifunctional catalytic activity for the HER and the UOR. Specifically, an overpotential of only 86 mV is needed to sustain a current density of 10 mA cm⁻² for the HER in alkaline media and a potential as low as 1.38 V at 10 mA cm⁻² is required for the UOR. Furthermore, the coupled HER and UOR system requires a low cell voltage of only 1.47 V at 10 mA cm⁻² with outstanding long-term durability, which is much lower than that for standard water electrolysis. This study is expected to provide new opportunities for the application of carbon dots in electrocatalysis.