As the bottleneck in photocatalytic water splitting, the oxygen evolution reaction (OER) has drawn huge attention, but its efficiency still falls short of expectations. A widely accepted speculation is that the catalysts’ activity is insufficient (high reaction barriers need to be overcome). Here, we develop a first-principles method to investigate the photocatalytic OER at the water/TiO₂(110) interface. A full mechanism uncovering the importance of radicals is determined. Kinetic analysis further enables to quantitatively estimate each possible obstacle in the process. We demonstrate unambiguously that the rate-determining factor of the OER varies with the concentration of surface-reaching photoholes (C_h+). Under experimental conditions, the intrinsic catalytic activity of TiO₂(110) does not represent the main obstacle, but all steps involving the photoholes are slow due to their low concentrations. This suggests that the key to enhance the OER efficiency is to increase C_h+ before C_h+ reaches the estimated threshold (C_h+ = ~10⁻⁴).

由于光催化水分解的瓶颈，氧气释放反应（OER）引起了极大的关注，但其效率仍未达到预期。广泛接受的推测是催化剂的活性不足（需要克服高反应障碍）。在这里，我们开发了一种第一原理的方法来研究水/ TiO ₂（110）界面上的光催化OER 。确定揭示自由基重要性的完整机制。动力学分析还使得能够定量估计过程中的每个可能的障碍。我们明确表明，OER的速率决定因素随表面到达光孔（C _{h +}）。在实验条件下，TiO ₂（110）的固有催化活性并不代表主要障碍，但是由于光孔的浓度低，所有涉及光孔的步骤都很缓慢。这表明提高OER效率的关键是在C _{h +}达到估计阈值（C _{h +}  =〜10 ^-4）之前增加C _{h +}。