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

A deep eutectic solvent (DES) prepared by mixing tetraalkylphosphonium chloride ([_P4444]Cl) and glycerol is applied in the synthesis of P-doped Ni materials. The DES not only serves as the reaction medium but also participates in the catalyst preparation. The synthesized P-doped Ni catalyst exhibits excellent performance in HER in both acidic and alkaline environments.

A deep eutectic solvent (DES) was prepared by mixing tetraalkylphosphonium chloride ([P₄₄₄₄]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. [P₄₄₄₄]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⁻², the overpotentials were only 90.2 and 115.9 mV, with a Tafel slope as low as 55.6 mV dec⁻¹. In an alkaline environment, the P-doped Ni also performed well. The η ₁₀ and η ₂₀ values were 107.0 and 145.4 mV, respectively. The Tafel slope was 57.0 mV dec⁻¹.

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