Bifunctional phosphorus-doped NiMo oxide/Ni–Fe hydroxide composite for overall water electrolysis: optimized performance with exceptional stability

The achievement of outstanding catalytic activity in water electrolysis is contingent upon the presence of abundant active sites with enhanced kinetics in electrocatalysts. This study focuses on enhancing the catalytic activity of water electrolysis under alkaline conditions by designing P-doped NiMo oxide/Ni–Fe hydroxide composite on Ni foam through a straightforward hydrothermal process. The composite is further annealed with NaH₂PO₄ and subjected to induced growth via in situ precipitation in an oxalic acid solution containing Fe precursors. The resulting bifunctional catalysts exhibit notable catalytic performance, manifesting overpotentials of 20.5 mV and 69.4 mV for the hydrogen evolution reaction (HER) and 225.9 mV and 271.8 mV for the oxygen evolution reaction (OER) to drive 10 and 100 mA/cm², respectively. The improved kinetics, attributed to P doping, play a pivotal role in reducing the overpotential of HER. Meanwhile, the homogeneous mixing of Ni and Fe, coupled with the large active surface area, enhances the catalytic performance of OER. The investigation of Mo precursors reveals their significant contribution to structurally shaping the catalysts, thereby influencing excellent OER performance. Collectively, these factors enable overall water electrolysis with low potentials of 1.82 V at 100 mA/cm², underscoring the efficacy of the developed bifunctional catalysts.