Enhancing Photocatalytic CO2 Conversion through Oxygen‐Vacancy‐Mediated Topological Phase Transition

Weak adsorption of gas reactants and strong binding of intermediates present a significant challenge for most transition metal oxides, particularly in the realm of CO2 photoreduction. Herein, we demonstrate that the adsorption can be fine‐tuned by phase engineering of oxide catalysts. An oxygen vacancy mediated topological phase transition in Ni‐Co oxide nanowires, supported on a hierarchical graphene aerogel (GA), is observed from a spinel phase to a rock‐salt phase. Such in situ phase transition empowers the Ni‐Co oxide catalyst with a strong internal electric field and the attainment of abundant oxygen vacancies. Among a series of catalysts, the in situ transformed spinel/rock‐salt heterojunction supported on GA stands out for an exceptional photocatalytic CO2 reduction activity and selectivity, yielding an impressive CO production rate of 12.5 mmol g−1 h−1 and high selectivity of 96.5 %. This remarkable performance is a result of the robust interfacial coupling between two topological phases that optimizes the electronic structures through directional charge transfer across interfaces. The phase transition process induces more Co2+ in octahedral site, which can effectively enhance the Co‐O covalency. This synergistic effect balances the surface activation of CO2 molecules and desorption of reaction intermediates, thereby lowering the energetic barrier of the rate‐limiting step. A topological phase transition, mediated by oxygen vacancies, is discovered in free‐standing Ni‐Co oxides supported on graphene aerogel. This phase transition introduces NiCoO2/NiCo2O4 heterojunction in the surface region, thus improving the catalytic activity thanks to a strong internal electric field and gradient oxygen vacancies. This synergistic effect balances the surface activation of CO2 and desorption of *CO intermediates, resulting in an exceptional photocatalytic CO2 reduction activity and selectivity.