Egawa Yuta, Kawaguchi Kei, Pan Zhenhua, Katayama Kenji
Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan.
J Chem Phys. 2024 Apr 28;160(16). doi: 10.1063/5.0203491.
Photocatalytic water-splitting represents a promising avenue for clean hydrogen production, necessitating an in-depth understanding of the photocatalytic reaction mechanism. The majority of the photocatalytic materials need cocatalysts to enhance the photo-oxidation or reduction reactions. However, the working mechanism, such as collecting charge carriers or reducing the reaction barrier, is not clear because they disperse inhomogeneously on a surface, and it is difficult to follow the local charge carrier behavior. This study employs the pattern-illumination time-resolved phase microscopy (PI-PM) method to unravel the spatial charge carrier behavior in photocatalytic systems, utilizing time-resolved microscopic image (refractive index change) sequences and their clustering analyses. This approach is robust for studying the change in local charge carrier behavior. We studied two major cocatalyst effects on photocatalysts: TiO2 with/without Pt and hematite with/without CoPi. The PI-PM method, supported by charge type clustering and the effects of scavengers, allowed for the analysis of local activity influenced by cocatalysts. This approach revealed that the introduction of cocatalysts alters the local distribution of charge carrier behavior and significantly impacts their decay rates. In TiO2 systems, the presence of Pt cocatalysts led to a local electron site on the micron scale, extending the lifetime to a few tens of microseconds from a few microseconds. Similarly, in hematite films with CoPi, we observed a notable accumulation of holes at cocatalyst sites, emphasizing the role of cocatalysts in enhancing photocatalytic efficiency. The study's findings highlight the complexity of charge carrier dynamics in photocatalytic processes and the significant influence of cocatalysts.
光催化水分解是一种很有前景的清洁制氢途径，需要深入了解光催化反应机理。大多数光催化材料需要助催化剂来增强光氧化或光还原反应。然而，其工作机制，如收集电荷载流子或降低反应势垒，尚不清楚，因为它们在表面上不均匀分散，并且难以追踪局部电荷载流子的行为。本研究采用图案照明时间分辨相显微镜（PI-PM）方法，利用时间分辨显微镜图像（折射率变化）序列及其聚类分析，揭示光催化体系中的空间电荷载流子行为。这种方法对于研究局部电荷载流子行为的变化非常有效。我们研究了助催化剂对光催化剂的两种主要影响：有/无Pt的TiO2以及有/无CoPi的赤铁矿。PI-PM方法在电荷类型聚类和清除剂作用的支持下，能够分析受助催化剂影响的局部活性。该方法表明，助催化剂的引入改变了电荷载流子行为的局部分布，并显著影响其衰减速率。在TiO2体系中，Pt助催化剂的存在导致了微米尺度上的局部电子位点，使寿命从几微秒延长到几十微秒。同样，在含有CoPi的赤铁矿薄膜中，我们观察到在助催化剂位点有空穴的显著积累，强调了助催化剂在提高光催化效率方面的作用。该研究结果突出了光催化过程中电荷载流子动力学的复杂性以及助催化剂的重大影响。
