Water splitting using semiconductor photoelectrodes is a promising approach to solar hydrogen production. Previous studies have well-demonstrated that electrochemical reduction (ER) pretreatment of bare and Ti-doped α-Fe₂O₃ electrodes enhances water photooxidation efficiencies, however, the mechanism underlying this improvement remains poorly understood. In this study, this was quantitatively investigated by multiple photoelectrochemical techniques and transient absorption spectroscopy, using the doped electrodes as examples. The results reveal that the kinetics of photoholes after moving to the electrode surface can be well described by a model of surface-state mediated charge transfer and recombination. The reason for the photocurrent enhancement is attributed to a significantly increased charge transfer rate constant (k_ct) and a decreased surface recombination rate constant (k_sr) by ER. The reason for the accelerated k_ct is that a new type of surface state, with a favorable energy position for water oxidation, is produced. The decreased k_sr is due to the reduced electron density at the surface of the semiconductor, resulted predominately from the negatively shifted flat band potential. These findings provide new insights into the mechanism of water photooxidation and enlighten a simple way to develop more efficient electrodes.

中文翻译：

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通过电化学还原预处理了解掺钛的α-Fe2O3电极上增强的光电化学水氧化

使用半导体光电极进行水分解是生产太阳能氢的一种有前途的方法。以前的研究已经公证明裸和Ti掺杂的α-Fe的电化学还原（ER）预处理₂ ö ₃电极提高了水的光氧化效率，但是，这种改进的机理尚不清楚。在这项研究中，以掺杂的电极为例，通过多种光电化学技术和瞬态吸收光谱法对其进行了定量研究。结果表明，通过表面状态介导的电荷转移和复合模型可以很好地描述光洞移动到电极表面后的动力学。光电流增强的原因归因于通过ER显着增加的电荷转移速率常数（k _ct）和降低的表面复合速率常数（k _sr）。k _ct加快的原因产生了一种新型的表面态，具有有利于水氧化的能量位置。k _sr的降低是由于半导体表面电子密度的降低所致，而电子密度的降低主要归因于负向移动的平带电势。这些发现提供了对水光氧化机理的新见解，并启发了开发更高效电极的简单方法。