As one of the most important photocatalysts, TiO₂ has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO₂ at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO₂ are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO₂ nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO₂ surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO₂ interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H₂ (H-H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.

中文翻译：

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自氢化壳促进了锐钛矿型TiO2上光催化H2的释放。

作为最重要的光催化剂之一，TiO ₂引发了数十年的广泛兴趣和深入的研究。在微观尺度上观察水和TiO ₂之间的界面反应可以提供对光催化过程机理的关键见解。当前，表征锐钛矿型TiO _2的光催化反应的实验方法主要限于水蒸气或单分子化学。在这里，我们使用液体环境透射电子显微镜研究了锐钛矿型TiO ₂纳米粒子在水中的光催化反应。在TiO ₂上观察到自氢化的壳氢气泡产生之前的表面。第一性原理计算表明，该壳是通过在TiO ₂水溶液界面处产生的光还原水质子的地下扩散而形成的，该质子通过减少H ₂（HH键）形成的活化势垒而促进光催化氢的释放。实验证实，自氢化壳包含还原的钛离子，并且随着紫外线照度的增加，其厚度可以增加到几纳米。