Understanding the Origin of High Quantum Efficiency in Photocatalytic Water Splitting of Al-Doped SrTiO ₃ from First-Principles Calculations

The aluminum (Al)-doped strontium titanate (SrTiO3, STO) photocatalyst has achieved an external quantum efficiency (EQE) of 96% in the overall water splitting reaction, far surpassing the approximately 10% EQE of traditional water-splitting photocatalysts. However, a comprehensive and systematic explanation of the origin of the high quantum efficiency in Al-doped STO and the intrinsic mechanism by which the dopant enhances the photocatalytic performance is still absent to date. In this work, we employ first-principles calculations to study the electronic structures and catalytic activities of STO (100), STO (110), and STO (210) facets. The calculated results clearly reveal that different STO facets exhibit the characteristic of band-edge misalignment. This misalignment endows the low-index STO (100) facet with the ability to capture photogenerated electrons, which are then applied to the hydrogen evolution reaction (HER). In contrast, high-index STO facets tend to preferentially capture photogenerated holes to drive the oxygen evolution reaction (OER), with the STO (210) facet, which has a higher valence-band alignment, showing relatively good performance. The oxygen vacancies can effectively activate the HER performance on the (100) facet, with the free energy change of the HER (ΔG*H) decreasing from 2.32 eV to 0.89 eV. Meanwhile, Al dopants are also capable of activating a lattice oxygen mechanism (LOM) pathway on the STO (210) facet, thereby leading to a further reduction in the OER overpotential from 0.86 V (the minimum OER overpotential within the adsorbate evolution mechanism (AEM) pathway) to 0.60 V, which boosts the catalytic activity of the OER. The low OER overpotential on the Al-doped STO (210) facet under the LOM pathway can be reasonably explained by the p-band center model. The facet-dependent defect regulation strategy enables cooperative optimization of HER and OER activities, providing a paradigm for designing photocatalysts with high quantum efficiency.