Sudrajat Hanggara, Kitta Mitsunori, Ito Ryota, Yoshida Tomoko, Katoh Ryuzi, Ohtani Bunsho, Ichikuni Nobuyuki, Onishi Hiroshi
Department of Chemistry, Graduate School of Science, Kobe University, Kobe 657-8501, Japan.
Phys Chem Chem Phys. 2021 Apr 14;23(14):8868-8879. doi: 10.1039/d1cp00375e. Epub 2021 Apr 6.
NaTaO, a semiconductor with a perovskite structure, has long been known as a highly active photocatalyst for overall water splitting when appropriately doped with La cations. A profound understanding of the surface feature and why and how it may control the water splitting activity is critical because redox reactions take place at the surface. One surface feature characteristic of La-doped NaTaO is a La-rich layer (shell) capping La-poor bulk (core). In this study, we investigate the role of the shell in core-shell-structured La-doped NaTaO through systematic chemical etching with an aqueous HF solution. We find that the La-rich shell plays a role in electron-hole recombination, electron mobility and water splitting activity. The shallow electron traps populating the La-rich shell trap the photoexcited electrons, decreasing their mobility. The shallowly trapped electrons remain reactive and are readily available on the surface to be extracted by the cocatalysts for the reduction reaction evolving H. The presently employed chemical etching method also confirms the presence of a La concentration gradient in the core that regulates the steady-state electron population and water splitting activity. Here, we successfully reveal the nanoarchitecture-photoactivity relationship of core-shell-structured La-doped NaTaO that thereby allows tuning of the surface features and spatial distribution of dopants to increase the concentration of photoexcited electrons and therefore the water splitting activity. By recognizing the key factors that control the photocatalytic properties of a highly active catalyst, we can then devise proper strategies to design new photocatalyst materials with breakthrough performances.
NaTaO 是一种具有钙钛矿结构的半导体，长期以来人们都知道，当适当掺杂 La 阳离子时，它是一种用于全分解水的高活性光催化剂。深入了解其表面特征以及它为何以及如何控制水分解活性至关重要，因为氧化还原反应发生在表面。La 掺杂的 NaTaO 的一个表面特征是富 La 层（壳层）覆盖贫 La 的主体（核）。在本研究中，我们通过用 HF 水溶液进行系统的化学蚀刻，研究了壳层在核壳结构的 La 掺杂 NaTaO 中的作用。我们发现富 La 壳层在电子 - 空穴复合、电子迁移率和水分解活性中起作用。填充在富 La 壳层中的浅电子陷阱捕获光激发电子，降低其迁移率。被浅捕获的电子仍然具有反应活性，并且很容易在表面上被用于还原反应生成 H 的助催化剂提取。目前采用的化学蚀刻方法还证实了核中存在 La 浓度梯度，该梯度调节稳态电子数量和水分解活性。在此，我们成功揭示了核壳结构的 La 掺杂 NaTaO 的纳米结构 - 光活性关系，从而能够调整表面特征和掺杂剂的空间分布，以增加光激发电子的浓度，进而提高水分解活性。通过认识到控制高活性催化剂光催化性能的关键因素，我们随后可以设计适当的策略来设计具有突破性性能的新型光催化剂材料。
