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.