In heterogeneous catalysis metal particle morphology and size can influence markedly the activity, both in heat-driven and in electro-photocatalytic conditions. Because of the intimate coupling between the photoelectron transfer and the surface catalytic reaction, it has been challenging to determine the optimal metal particle size in photocatalytic reactions. Here, we utilize ab initio molecular dynamics and hybrid density functional theory calculations to reveal the size-dependent activity of photocatalytic hydrogen evolution reaction (HER) over Pt/TiO₂ photocatalysts. By supporting four different Pt particles Pt₅, Pt₈, Pt₁₃, and Pt₁₉ on anatase TiO₂(101), we determine the optimal geometries, the electronic structures, the photoelectron-transfer efficiency, and the surface hydrogen coupling reaction activity of these composite materials. We demonstrate that very small Pt clusters with less than two atomic layers are efficient photoelectron collectors from TiO₂ bulk due to their low highest occupied molecular orbital level with respect to the oxide conduction band; by contrast, larger particles with more than two Pt layers are the active site for hydrogen coupling to catalyze HER. Our results suggest that quasi two-Pt-layer particles, corresponding to ∼1 nm size, are the best catalyst for photocatalytic HER. Compared to heat-driven and electrocatalysis, we conclude that photocatalysis prefers even smaller metal particles to enhance photoelectron transfer, which should be a general guideline for designing optimal photocatalysts in the future.

中文翻译：

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DFT研究揭示了铂助催化剂在TiO ₂载体上光催化制氢的尺寸效应

在非均相催化中，在热驱动和电光催化条件下，金属颗粒的形态和大小都会显着影响其活性。由于光电子转移与表面催化反应之间存在紧密的耦合，因此在光催化反应中确定最佳的金属粒径一直是一项挑战。在这里，我们利用从头算分子动力学和混合密度泛函理论计算来揭示Pt / TiO ₂光催化剂上光催化氢释放反应（HER）的尺寸依赖性活性。通过在锐钛矿型TiO ₂上支撑四个不同的Pt颗粒Pt ₅，Pt ₈，Pt ₁₃和Pt ₁₉（101），我们确定这些复合材料的最佳几何形状，电子结构，光电子转移效率和表面氢偶联反应活性。我们证明具有少于两个原子层的非常小的Pt团簇是TiO _2的有效光电子收集器由于它们相对于氧化物导带具有较低的最高占据分子轨道能级，因此具有体积；相比之下，具有两个以上Pt层的较大颗粒是氢偶联催化HER的活性中心。我们的研究结果表明，相当于1 nm大小的准两层Pt颗粒是光催化HER的最佳催化剂。与热驱动和电催化相比，我们得出的结论是，光催化更喜欢使用较小的金属颗粒来增强光电子转移，这应该是将来设计最佳光催化剂的一般指南。