The synergetic effect of the mixed phase of NiMoO4 with a 1D–2D–3D hierarchical structure for a highly efficient and stable urea oxidation reaction

Abstract

Using a urea oxidation reaction (UOR) instead of an oxygen evolution reaction (OER) is regarded as an effective method for reducing the required hydrogen potential and overall energy costs. Nickel molybdate (NiMoO₄) is considered as an efficient UOR catalyst, and its crystalline phase plays a pivotal role in improving the UOR activity. However, a deep understanding of the relevant mechanism of the NiMoO₄ phase remains largely ambiguous. Herein, a mixed phase (α/β) of the NiMoO₄@NF electrode with a 1D–2D–3D hierarchical structure is fabricated using a facile solvothermal strategy. This unique 1D–2D–3D hierarchical structure is conducive to exposing more abundant active sites. The experiments and density functional theory (DFT) calculations jointly demonstrate that α/β-NiMoO₄ can bring “1 + 1 > 2” multiphase synergetic effects, higher conductivity and lower adsorption energy of urea molecules, which is beneficial for improving the UOR performance. Consequently, the α/β-NiMoO₄@NF electrode exhibits a decent UOR activity, i.e., at a potential of 1.36 V to reach 100 mA cm⁻², about 315 mV less than that of the OER. This study provides a promising method for energy conservation and treatment of urea-containing wastewater.