Synergistic Effect of N-NiMoO4/Ni Heterogeneous Interface with Oxygen Vacancies in N-NiMoO4/Ni/CNTs for Superior Overall Water Splitting

The exploring of economical, high-efficiency, and stable bifunctional catalysts for hydrogen evolution and oxygen evolution reactions (HER/OER) is highly imperative for the development of electrolytic water. Herein, a 3D cross-linked carbon nanotube supported oxygen vacancy (V_o)-rich N-NiMoO₄/Ni heterostructure bifunctional water splitting catalyst (N-NiMoO₄/Ni/CNTs) is synthesized by hydrothermal-H₂ calcination method. Physical characterization confirms that V_o-rich N-NiMoO₄/Ni nanoparticles with an average size of ≈19 nm are secondary aggregated on CNTs that form a hierarchical porous structure. The formation of Ni and NiMoO₄ heterojunctions modify the electronic structure of N-NiMoO₄/Ni/CNTs. Benefiting from these properties, N-NiMoO₄/Ni/CNTs drives an impressive HER overpotential of only 46 mV and OER overpotential of 330 mV at 10 mA cm⁻², which also shows exceptional cycling stability, respectively. Furthermore, the as-assembled N-NiMoO₄/Ni/CNTs||N-NiMoO₄/Ni/CNTs electrolyzer reaches a cell voltage of 1.64 V at 10 mA cm⁻² in alkaline solution. Operando Raman analysis reveals that surface reconstruction is essential for the improved catalytic activity. Density functional theory (DFT) calculations further demonstrate that the enhanced HER/OER performance should be attributed to the synergistic effect of V_o and heteostructure that improve the conductivity of N-NiMoO₄/Ni/CNTs and facilitatethe desorption of reaction intermediates.