Spatiotemporal alignment of hole transfer and water oxidation for highly efficient photocatalytic water splitting

Photocatalytic overall water splitting remains limited by inefficient charge separation and utilization in reactions. Al-doped SrTiO₃ exhibiting near-100% apparent quantum efficiency for overall water splitting indicates nearly complete charge separation and surface catalytic efficiency. Although Al doping has been assumed to enhance charge separation and transfer, the exact role of Al is still unclear. Here, using spatiotemporal surface photovoltage imaging, we show that a gradient Al doping in Al-doped SrTiO₃ generates a built-in electric field that drives photogenerated holes from the bulk toward surface trap sites in the form of hydroxylated Al-O-Ti, prolonging their lifetime from ~100 ns to 10 ms. Spectroscopic analyses reveal that these hydroxylated Al sites serve as key centers for water adsorption, facilitating water oxidation. These findings underscore the pivotal role of Al in the spatiotemporal alignment of hole transfer and surface catalytic water oxidation, enabling high-efficiency photocatalysis in overall water splitting.