Controllable synthesis of ultrathin Co₃O₄ and construction of RuO₂/Co₃O₄ interface for oxygen evolution performance

Replacing noble metal catalysts with transition metal oxides is a key goal in catalysis research. However, obtaining well-defined ultrathin oxides remains challenging, unlike the relatively facile preparation of typical ultrathin crystals. Here, we report the vapor-liquid-solid (VLS) growth of ultrathin Co₃O₄ nanostructures, using CoCl₂ as the precursor in combination with an oxygen-containing atmosphere. Single-crystalline, micrometer-scale, thickness-tunable epitaxial Co₃O₄ nanosheets were successfully synthesized on Al₂O₃(0001) substrates and displayed favorable oxygen evolution activity following the loading of RuO₂. During the growth process, the cobalt-containing liquid intermediate and the dynamic liquid-solid interface play crucial roles in guiding the epitaxial alignment and promoting expansion of the oxide layer. This method enables the fabrication of structurally well-defined Co₃O₄ with tunable surface morphology and crystallographic orientation, and offers an ideal model system for investigating structure-dependent catalytic mechanisms and surface reactivity in transition metal oxide catalysts.