Preparation of P-Doped Ni Catalyst Using Deep Eutectic Solvents and Its Excellent Hydrogen Evolution Performance in Water Splitting.

A deep eutectic solvent (DES) was prepared by mixing tetraalkylphosphonium chloride ([P]Cl) and glycerol in a 1:2 molar ratio. Nickel nitrate was dissolved in this DES, and then the mixture was heated at 350 °C to obtain phosphorus-doped nickel catalysts. In this system, the DES plays multiple crucial roles. (1) It serves as a reaction medium, providing a suitable solvent environment for the synthesis of Ni-based catalysts. (2) It actively participates in the catalyst preparation as a reactant. [P]Cl acts as a P source, while glycerol effectively promotes the formation of nickel metal as a reducing agent. (3) It exhibits a templating effect, inducing the morphology of product to be a unique thin sheet with angular edges. The synthesized P-doped Ni material exhibits excellent hydrogen evolution performance in water splitting. In an acidic environment, when the current densities reached 10 and 20 mA cm, the overpotentials were only 90.2 and 115.9 mV, with a Tafel slope as low as 55.6 mV dec. In an alkaline environment, the P-doped Ni also performed well. The η and η values were 107.0 and 145.4 mV, respectively. The Tafel slope was 57.0 mV dec.