As far as we know, the CO2 photoconversion reaction with H2O includes two important steps. One step is CO2 photoreduction (photogenerated electrons) while the other step is the oxidation of water (photogenerated holes). It is obvious that the oxidation of water is also the key step in the CO2 photoconversion reaction. However, little research has been done to improve the oxidation of water, thereby indirectly improving the photocatalytic CO2 reduction property of TiO2. Moreover, CO2 adsorption capacity is also considered as an important limiting factor for the CO2 photoconversion activity. Therefore, in this paper, CoPi (an amorphous cobalt-phosphate-based material) with high CO2 adsorption capacity was successfully immobilized on the surface of TiO2 nanosheets and served as a hole-cocatalyst to trap holes, thereby delaying the recombination of photogenerated electrons and holes and providing more CO2 gas to take part in the CO2 reduction reaction. Hence, the TiO2/CoPi exhibited much better CO2 photoconversion performance in water compared to pristine TiO2.