Interfacial electron redistribution in a TiO2/Mn3O4 hollow heterostructure for selective photocatalytic CO2-to-CO conversion.

Selective photocatalytic CO2-to-CO conversion remains challenging because of rapid charge recombination and insufficient CO2 activation. Herein, a TiO2/Mn3O4 hollow heterostructure was constructed through a SiO2 hard-template strategy combined with in situ growth. The hollow hemispherical architecture provides an open and accessible structural platform for the in situ growth of Mn3O4 nanosheets and the construction of intimate TiO2/Mn3O4 heterointerfaces. Uniformly anchored Mn3O4 nanosheets establish intimate heterointerfaces that induce interfacial electron redistribution and promote charge separation. As a result, TiO2/Mn3O4 exhibits a CO evolution rate of 9.31 μmol g-1 h-1, which is 1.62 and 2.20 times higher than those of pristine TiO2 and Mn3O4, respectively, together with a CO selectivity of 84.03%, an electron selectivity of 56.81%, and excellent cycling stability. X-ray photoelectron spectroscopy analysis reveals pronounced interfacial electronic redistribution between TiO2 and Mn3O4, while photoelectrochemical measurements demonstrate enhanced charge separation and interfacial charge transfer. In situ diffuse reflectance infrared Fourier transform spectroscopy further confirms the preferential formation of *COOH and *CO intermediates, favoring the selective two-electron CO2-to-CO conversion pathway. This work demonstrates that regulating interfacial electron redistribution through hollow heterostructure engineering is an effective strategy for achieving efficient and selective photocatalytic CO2-to-CO conversion.