Heterojunction-Induced Rapid Transformation of Ni³⁺/Ni²⁺ Sites which Mediates Urea Oxidation for Energy-Efficient Hydrogen Production.

Abstract

Water electrolysis is an environmentally-friendly strategy for hydrogen production but suffers from significant energy consumption. Substituting urea oxidation reaction (UOR) with lower theoretical voltage for water oxidation reaction adopting nickel-based electrocatalysts engenders reduced energy consumption for hydrogen production. The main obstacle remains strong interaction between accumulated Ni³⁺ and *COO in the conventional Ni³⁺-catalyzing pathway. Herein, a novel Ni³⁺/Ni²⁺ mediated pathway for UOR via constructing a heterojunction of nickel metaphosphate and nickel telluride (Ni₂P₄O₁₂/NiTe), which efficiently lowers the energy barrier of UOR and avoids the accumulation of Ni³⁺ and excessive adsorption of *COO on the electrocatalysts, is developed. As a result, Ni₂P₄O₁₂/NiTe demonstrates an exceptionally low potential of 1.313 V to achieve a current density of 10 mA cm^-2 toward efficient urea oxidation reaction while simultaneously showcases an overpotential of merely 24 mV at 10 mA cm^-2 for hydrogen evolution reaction. Constructing urea electrolysis electrolyzer using Ni₂P₄O₁₂/NiTe at both sides attains 100 mA cm^-2 at a low cell voltage of 1.475 V along with excellent stability over 500 h accompanied with nearly 100% Faradic efficiency.