Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions
Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions
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DOI：
10.1021/acsami.8b05190
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发表时间：
2019-02-13
影响因子：
9.5
通讯作者：
Wang, Dunwei
中科院分区：
文献类型：
--
作者：
Li, Wei;Yang, Ke R.;Wang, Dunwei
光电化学（PEC）系统的性能在很大程度上取决于光电-电解质界面的电荷分离、传输和转移特性。在影响电荷行为的因素中，与电解质接触的半导体的晶面起着重要的作用，但以前研究得很少。在这里，我们提出了一项研究，旨在了解如何不同方面的赤铁矿影响太阳能水氧化反应中的电荷分离和转移行为。具体地，合成了具有主要暴露的{012}和{001}晶面的赤铁矿微晶。密度泛函理论（DFT）计算表明，赤铁矿{012}表面具有较高的OH覆盖度，这是由X射线光电子能谱（XPS）证实。这些表面OH基团作为活性位点介导水氧化反应，这对PEC系统起着积极的作用。这些表面OH基团还促进电荷复合，这损害了赤铁矿的电荷分离能力。事实上，强度调制光电流光谱（IMPS）证实，赤铁矿{012}表面表现出较高的速率常数的电荷转移和重组。开路电位（OCP）的测量表明，赤铁矿{012}表面表现出更大程度的费米能级钉扎效应。我们的研究结果揭示了如何不同的表面晶体结构可能会改变表面动力学和能量。这些信息预计将有助于优化实际太阳能燃料合成的PEC性能。
The performance of a photoelectrochemical (PEC) system is highly dependent on the charge separation, transport and transfer characteristics at the photoelectrodel electrolyte interface. Of the factors that influence the charge behaviors, the crystalline facets of the semiconductor in contact with the electrolyte play an important role but has been poorly studied previously. Here, we present a study aimed at understanding how the different facets of hematite affect the charge separation and transfer behaviors in a solar water oxidation reaction. Specifically, hematite crystallites with predominantly {012} and {001} facets exposed were synthesized. Density functional theory (DFT) calculations revealed that hematite {012} surfaces feature higher OH coverage, which was confirmed by X-ray photoelectron spectroscopy (XPS). These surface OH groups act as active sites to mediate water oxidation reactions, which plays a positive role for the PEC system. These surface OH groups also facilitate charge recombination, which compromises the charge separation capabilities of hematite. Indeed, intensity modulated photocurrent spectroscopy (IMPS) confirmed that hematite {012} surfaces exhibit higher rate constants for both charge transfer and recombination. Open circuit potential (OCP) measurements revealed that the hematite {012} surface exhibits a greater degree of Fermi level pinning effect. Our results shed light on how different surface crystal structures may change surface kinetics and energetics. The information is expected to contribute to efforts on optimizing PEC performance for practical solar fuel synthesis.