a. The formation of oxygen vacancies (Vo) inside the mesocrystals and band structure. Depletion layers of less than 1nm promote the electron division and water oxidation. CB: Conduction Band, VB: Valence Band, e-: electron, h+: hole.
b. In accordance to the potential gradient, a large amount of holes accumulated on the particle surface and oxidized the water, leading to a large decrease in the activation energy (Ea) and improving the conversion rate.