Crystalline/amorphous c-NiMo/a-NiMoOx nanoarrays for urea-assisted energy-saving H2 production in alkaline seawater†

Abstract

Electrocatalytic seawater splitting is regarded as the most effective method for producing green hydrogen (H₂), but it faces issues of high energy consumption and harmful chlorine evolution side reactions. Replacing the sluggish oxygen evolution reaction (OER) with the thermodynamically favorable urea oxidation reaction (UOR) would enable energy-saving and chlorine-free H₂ production. Herein, a novel three-dimensional (3D) structured electrocatalyst (c-MoNi/a-NiMoO_x) with crystalline MoNi alloy clusters coupled with amorphous NiMoO_x nanowires is reported. In the hydrogen evolution reaction (HER) process, the electron redistribution at the crystalline/amorphous interface could effectively regulate the electronic structure, thereby optimizing the Gibbs free energy of water dissociation and hydrogen adsorption. In the UOR process, c-MoNi/a-NiMoO_x undergoes surface reconstruction to form highly active β-NiMoOOH. The incorporation of Mo lowers the activation energy barrier of the rate-determining step, thus facilitating the progression of the multi-step UOR process. Excitingly, the urea-assisted seawater electrolysis based on c-MoNi/a-NiMoO_x requires an ultralow voltage of 1.68 V to deliver 500 mA cm⁻², and displays distinguished long-term stability to keep above 100 mA cm⁻² for 300 h. This work may show practical impact on designing efficient electrocatalysts for combing seawater splitting with urea purification.