Low\npH-Induced Activation\nof Single-Atom Pt Sites\non TiO<sub>2</sub> for Enhanced Photocatalytic H<sub>2</sub> Evolution

The application of single atoms (SAs)\nhas emerged as\na cutting-edge\napproach to the cost-efficient utilization of noble metals in catalytic\nprocesses. However, the performance of SA systems under various acidity\nconditions has been barely investigated. Here, we use Pt SA cocatalysts\nanchored on thin TiO<sub>2</sub> films as a model system, which shows\na 2.3–3.2-fold enhanced H<sub>2</sub> evolution performance\nat pH = 1, as compared to less acidic conditions (pH = 6 and 14, respectively),\nwith a remarkable turnover frequency (TOF) of up to 589 #H<sub>2</sub> site<sup>–1</sup> s<sup>–1</sup>. Based on variations\nin H<sub>2</sub> evolution performance at different pH and Pt loadings,\nit is clear that activation of additional Pt sites takes place in\nacidic conditions, which is ascribed to changes in H-binding energy.\nThis allows better utilization of Pt SAs at high loadings and low\nlight intensities. Despite the partial agglomeration of Pt SAs, within\n4 h, a steady surface configuration of Pt sites with abundant SAs\nis established, which correlates with the stabilization of the H<sub>2</sub> evolution rate. This research demonstrates a route to extend\nthe limit of photocatalytic H<sub>2</sub> generation with suitable\nSAs and reaction conditions.