Efficient generation of H₂via water-splitting is an underpinning technology for realizing the hydrogen economy. However, the sluggish anodic oxygen evolution reaction (OER) requires a large energy input. Low-cost, transition metals such as NiFe oxides/hydroxides have been regarded as one of the most efficient catalysts for the OER in alkaline media, although the detailed mechanisms remain debated due to the lack of direct evidence for the proposed active sites during the catalytic processes. Herein, we show a NiFe (oxy)hydroxide catalyst doped with a third metal Cr prepared by facile electrodeposition to achieve further enhanced activity for the OER. Operando Raman and X-ray absorption spectroscopy (XAS) characterisation were employed to detect the formation of active intermediates and M–O bonds on active sites during the OER process. For the host NiFe (oxy)hydroxide catalyst, the shorter Fe–O in the Fe-substituted-β-NiOOH intermediate is observed as active sites for the OER. A Cr, Fe-substituted-β-NiOOH intermediate is detected in the enhanced NiFeCr (oxy)hydroxide catalyst where Cr is oxidized into the 6+ valence state with optimal Cr–O bonds, adding new active sites to boost the OER. Density functional theory (DFT) calculations support the operando spectroscopic observations and reveal the lower overpotential at the Cr⁶⁺ sites in the NiFeCr oxyhydroxide intermediate than the Fe³⁺ sites in the NiFe oxyhydroxide intermediate. This study demonstrates a strategy for designing highly active OER catalysts by introducing high valence metals into oxides/hydroxides to further enhance the kinetics of water oxidation.

Electrocatalytic water splitting offers a promising route to sustainable H₂, but the oxygen evolution reaction (OER) in alkaline media remains the principal bottleneck for activity and durability. This review focuses on alkaline OER and integrates mechanism, kinetics, materials design, and cell-level considerations. Reaction mechanisms are outlined, including the adsorbate evolution mechanism (AEM) and the lattice oxygen mediated mechanism (LOM), together with universal scaling constraints and operando reconstruction of precatalysts into active oxyhydroxides. Strategies for electronic tuning, defect creation, and heterointerface design are linked to measurable kinetics, including iR-corrected overpotential, Tafel slope, charge transfer resistance, and electrochemically active surface area (ECSA). Representative catalyst families are critically evaluated, covering Ir and Ru oxides, Ni-, Fe-, and Co-based compounds, carbon-based materials, and heterostructure systems. Electrolyte engineering is discussed, including control of Fe impurities and cation and anion effects, and gas management at current densities of 100–500 mA·cm⁻² and higher. Finally, we outline challenges and directions that include operando discrimination between mechanisms and possible crossover between AEM and LOM, strategies to relax scaling relations using dual sites and interfacial water control, and constant potential modeling with explicit solvation and electric fields to enable efficient, scalable alkaline electrolyzers.

The utilization of hydrazine as a reducing agent in the electroless cobalt bath is indispensable for the application of pure cobalt film fabrication in ultra-large-scale integration (ULSI). However, the deposition rate using the ordinary coating bath is relatively low. After conducting numerous experiments in this study, we have made a groundbreaking discovery: the deposition rate of electroless plating pure cobalt bath can be significantly increased from less than 1.0 μ·h⁻¹ to more than 5.0 μ·h⁻¹ by adding triethanolamine (TEA) as an accelerator. This remarkable finding greatly enhances the practical value of the electroless cobalt plating bath and enables its application in microholes filling of cobalt interconnect lines below 10 nm. According to the results of linear sweep voltammetry and mixed potential theory, the addition of TEA essentially forms [Co(C₆H₅O₇)(TEA)₂]₂ ²⁻ complex with more feasible reductivity than that of the [Co(C₆H₅O₇)(H₂O)]₂ ²⁻ in the ordinary plating bath and the cobalt center is favorable to be released under the electroless reduction attack to the unstably strong steric hindrance of TEA, which significantly increases the reduction current of Co(II) ions. After the further optimization of pH, temperature and annealing process, not only does resistivity decrease to 12.1 μΩ·cm, but also the surface morphology and crystallinity improve significantly. Therefore, an applicable electroless cobalt plating protocol with a moderate deposition rate is obtained.