Nitrogen-doped mesoporous nickel cobaltite for oxygen evolution and urea oxidation reactions

Abstract

Doping nitrogen atoms into spinel metal oxides enhances the electrical conductivity and boosts the catalytic active sites, which are favorable properties for catalytic applications such as oxygen evolution reaction (OER) and urea oxidation reaction (UOR). However, nitrogen doping approach suffers from lack of exposed surface sites, complicated process, and required expensive gas source, limiting their efficiency and implementation. In this study, a two-step process, combining self-assembly strategy, followed by hydrazine vapor treatment was employed to synthesize a nitrogen-doped mesoporous spinel nickel cobalt oxide catalyst (N@m-NiCo₂O₄) active for both OER and UOR. Structural modulation via self-assembly produced a mesoporous architecture with an enlarged surface area, which facilitated hydrazine vapor diffusion, enabling effective nitrogen doping, the formation of abundant oxygen vacancies, and enhanced electrical conductivity. As a result, the N@m-NiCo₂O₄ catalyst exhibited excellent OER activity, with an onset potential of 1.49 V and a Tafel slope of 44 mV dec^‑1, as well as outstanding UOR performance, delivering a low overpotential of 330 mV at a high current density of 500 mA cm^-2. These findings highlight the importance of integrating a porous structural design with improved electrical conductivity to achieve superior catalytic efficiency. This effective strategy may also be extended to other spinel metal oxides for diverse electrochemical energy applications.