Ultrafine Ni-Doped FeOOH Nanoparticles with Rich Oxygen Vacancies to Promote Oxygen Evolution

Nickel iron hydroxide oxide is one of the efficient catalysts for oxygen evolution reaction (OER). However, current synthesis methods, such as solvothermal and electrodeposition, require stringent experimental conditions (e.g., temperature, pressure, and solvent) and involve complex procedures with high costs. To address this issue, we developed a simple and efficient electrostatic self-assembly strategy to synthesize Ni-doped iron oxyhydroxide (Ni-FeOOH) by combining aminated two-dimensional g-C3N4 with trace amounts of Ni2+ and Fe2+, forming a tightly integrated heterostructure (Ni-FeOOH@g-C3N4). This method is notable for its simplicity and ability to produce ultrasmall Ni-FeOOH nanoparticles (∼1.9 nm), which significantly enhance the active surface area and functional sites. The resulting catalyst exhibits exceptional OER performance, achieving a low overpotential of 260 mV at 10 mA·cm-2 and demonstrating long-term stability. Remarkably, despite containing only trace amounts of Ni (2.46%) and Fe (3.36%), Ni-FeOOH@g-C3N4 delivers a high turnover frequency of 3.96 s-1, outperforming many conventional hydroxyl oxides. The improved performance is attributed to the ultrasmall particle size and the presence of excessive oxygen vacancies, which lower the energy barrier for O* formation and accelerate OER kinetics. This work proposes a method for constructing efficient catalysts with trace active metals to improve the OER activity.