Photoelectrochemical water splitting has attracted significant attention as an environment-friendly method to generate H₂ and O₂. Electrodes composed of powders exhibit a large surface area and are favorable for surface reactions; however, their high resistance prevents charge transportation. In contrast, photoelectrodes composed of a dense film exhibit high conductivity; however, they constitute a small surface area. Therefore, a combination of these two films can lead to higher photoelectrochemical activities. Herein, a particulate/dense TiO₂ hybrid electrode exhibited eightfold and twofold higher activities for water oxidation at sufficiently positive potentials as compared to those of the single particulate and dense film electrodes, respectively. Electrochemical impedance measurements and the light intensity dependence of the photocurrent suggest that the activity enhancement is responsible for the synergistic effects of effective charge separation in the highly conductive dense TiO₂ film and effective hole-consuming reaction at the particulate TiO₂ layer. However, the activity rather decreased near the onset potential of water oxidation (<0.3 V) under the illumination of light near the bandgap energy (375 nm). Such an activity decrease was not observed for the 340 nm illumination; hence, the recombination of charge carriers generated in dense and particulate layers is responsible: the charge transfer resistance at the particulate/dense interface prevents the effective charge separation. These results demonstrate that the combination of particulate matter and dense films can produce a synergistic effect; however, the resistance at the junction remains a significant bottleneck, rendering resistance reduction necessary to maximize the advantages of hybrid electrodes, especially under the illumination of longer wavelength light.

中文翻译：

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通过颗粒/致密双层形成增强TiO2电极的光电化学活性。

作为产生H ₂和O _2的一种环境友好的方法，光电化学水分解法引起了广泛的关注。由粉末组成的电极具有较大的表面积，有利于表面反应。但是，它们的高电阻阻止电荷传输。相反，由致密膜组成的光电极显示出高电导率。但是，它们构成较小的表面积。因此，这两种膜的组合可以导致更高的光电化学活性。此处，颗粒/致密TiO ₂与单个颗粒电极和致密膜电极相比，混合电极分别在足够正的电势下对水的氧化表现出八倍和两倍的活性。电化学阻抗测量和光电流的光强度依赖性表明，活性增强是高导电致密TiO ₂膜中有效电荷分离和颗粒TiO _2上有效空穴消耗反应的协同效应的原因。层。但是，在带隙能量（375 nm）附近的光照射下，水氧化的起始电位（<0.3 V）附近的活性反而降低了。对于340nm的照射没有观察到这种活性降低。因此，致密层和颗粒层中产生的电荷载流子的重组是负责的：颗粒/致密界面处的电荷转移阻力会阻止有效的电荷分离。这些结果表明，颗粒物和致密膜的结合可以产生协同作用。然而，结处的电阻仍然是一个很大的瓶颈，因此必须降低电阻才能最大化混合电极的优势，尤其是在较长波长的光照射下。