Ba–Ni–Ge Clathrate Transformation Maximizes Active Site Utilization of Nickel for Enhanced Oxygen Evolution Performance

Discovering novel oxygen evolution reaction (OER) (pre)catalysts with exceptional catalytic activity and long-term stability is pivotal for advancing decarbonization technologies. In this study, we present the ternary Ba₈Ni₆Ge₄₀ phase with an open clathrate structure exhibiting remarkable performance in alkaline OER. When integrated into an alkaline water electrolyzer, this clathrate precatalyst achieves high stability under a sustained current density of ∼550 mA cm^-2 for 10 days. By combining in situ Raman spectroscopy, quasi in situ X-ray absorption spectroscopy, and (micro)structural characterizations, we elucidate the complete electrochemical transformation of Ba₈Ni₆Ge₄₀ (~90 weight% leaching) forming ultrathin nanosheets composed of a porous and defective NiOOH nanostructure with maximized accessible active site exposure. Notably, a reversible phase transition mainly between Ni(OH)₂ and NiOOH has also been established in the electrochemical redox process. Meanwhile, the successful application of the model Ba₈Ni₆Ge₄₀ precatalyst represents a promising new class of functional inorganic materials for water electrolysis.