Nickel molybdate nanorod array as a dual-function electrocatalyst for urea oxidation and hydrogen evolution in urea-assisted water splitting

Abstract

In the urea-assisted water splitting, the superhydrophilic and superaerophobic NiMoO₄ nanoarray catalyst can significantly enhance both the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER). In contrast, the aggregated Ni(OH)₂ catalyst promotes UOR but reduces HER kinetics in the presence of urea. Coral-like NiMoO₄ nanorods with mixed α and β phases can be supported on nickel foam (NF) under hydrothermal conditions with phosphomolybdic acid. Conversely, α-Ni(OH)₂ forms aggregated microspheres on NF without it. A synergistic effect between Ni and Mo modulates the electronic structure of NiMoO₄ that enhances the catalytic activity, superhydrophilicity, and electrical conductivity. The NF@NiMoO₄ exhibits superior catalytic performance, as demonstrated by its low Tafel slope of 14.7 mV dec⁻¹ for UOR and 77.3 mV dec⁻¹ in magnitude for HER. The hydrated NF@NiMoO₄ nanoarray enhances wettability and increases the active surface area for catalytic reactions in UOR and HER compared to NF@Ni(OH)₂. Its configuration provides a superaerophobic surface and enables rapid transport of electrons, electrolytes, and gas bubbles. Consequently, NF@NiMoO₄ offers abundant active sites, strong substrate interactions, and efficient gas release, making it a promising dual-function electrocatalyst for urea-assisted water splitting.