Kumar Amol, Li Jingguo, Beiler Anna M, Ott Sascha
Department of Chemistry─Ångström Laboratory, Uppsala University, P.O. Box 523, 75237 Uppsala, Sweden.
Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.
J Am Chem Soc. 2025 Jun 25;147(25):21996-22002. doi: 10.1021/jacs.5c05700. Epub 2025 Jun 10.
Surface modification is an effective method to realize high performance photoelectrodes. While current investigations mostly aim to leverage surface layers for improved charge carrier kinetics during charge separation, interfacial charge transfer, and decreased recombination, carrier transport within the surface layer is largely unattended. Herein, we explore this charge transport process on a model photocathode consisting of p-Si and GaP semiconductors (SCs) that are coated with a redox-active Zn-NDI (NDI = naphthalene diimide bis-pyrazolate) metal-organic framework (MOF) surface layer. The MOF layer is able to accept photogenerated electrons and support a large photovoltage of the underlying SC. In addition to well-established carrier generation and interfacial transfer processes that are frequently considered to control photocurrents, experimental photoelectrochemical data of the MOF@SC electrodes expose limitations that arise from electron transport in the surface layer coating. The transport-limited regime becomes relevant when the illumination intensity is gradually increased and is sensitive to the nature of the underlying semiconductor as well as the electrolyte. The phenomenon reported in this work is likely present in other surface-modified photoelectrodes with thick cocatalysts or redox-active polymer coatings but can easily be overlooked. In the MOF@SC construct, the transition between different limiting regimes can be visualized owing to the well-behaved cation-coupled photoelectron hopping transport in the MOF layer. These findings support the design and realization of efficient photoelectrodes.
表面改性是实现高性能光电极的有效方法。虽然目前的研究大多旨在利用表面层来改善电荷分离、界面电荷转移过程中的载流子动力学，并减少复合，但表面层内的载流子传输在很大程度上未得到关注。在此，我们在一个由p-Si和GaP半导体（SCs）组成的模型光阴极上探索这种电荷传输过程，该光阴极涂覆有氧化还原活性的Zn-NDI（NDI = 萘二酰亚胺双吡唑酸盐）金属有机框架（MOF）表面层。MOF层能够接受光生电子并支持下层半导体产生较大的光电压。除了经常被认为控制光电流的成熟的载流子产生和界面转移过程外，MOF@SC电极的实验光电化学数据揭示了表面层涂层中电子传输所带来的局限性。当光照强度逐渐增加时，传输受限状态变得显著，并且对下层半导体的性质以及电解质敏感。这项工作中报道的现象可能存在于其他具有厚助催化剂或氧化还原活性聚合物涂层的表面改性光电极中，但很容易被忽视。在MOF@SC结构中，由于MOF层中良好的阳离子耦合光电子跳跃传输，可以观察到不同受限状态之间的转变。这些发现为高效光电极的设计和实现提供了支持。
