Water splitting to produce H₂ and O₂ is a fundamental reaction for artificial photosynthesis on semiconductor photocatalysts. The mechanism of the multistepped reaction, especially four-electron oxidation to O₂, has not yet been understood. Although some intermediate states have been detected in transient spectroscopy, O₂ evolution kinetics remain unknown at the end of consecutive reaction steps. We apply operando O₂ detection with a microelectrode to determine the absolute evolution rate on a highly efficient SrTiO₃ photocatalyst film casted on a glass plate. The evolution rate was determined with a time resolution of 0.1 s, which was improved by 1000 times compared with that in widely used gas-chromatographic detection. The observed rate did not respond instantaneously to excitation light irradiation. When light was turned on, the photocatalyst film was inactive for evolution and light-activated in seconds. It was proposed that the first absorbed photons were consumed to fill trap states on SrTiO₃ surface and then the latter photons drove steady O₂ evolution. When excitation light stopped, the O₂ evolution rate exponentially decayed in seconds. The microelectrode method demonstrated herein will be useful for understanding many other reaction kinetics at liquid–solid interfaces.

中文翻译：

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O ₂在光催化水分解反应中的瞬态动力学

分解产生H ₂和O _2的水是在半导体光催化剂上进行人工光合作用的基本反应。多步反应的机理，特别是四电子氧化为O ₂的机理尚不清楚。尽管在瞬态光谱学中已经检测到一些中间状态，但是在连续反应步骤结束时，O ₂的释放动力学仍然未知。我们使用微电极操作O ₂检测来确定高效SrTiO ₃上的绝对演化速率在玻璃板上浇铸的光触媒膜。用0.1 s的时间分辨率确定析出速率，与广泛使用的气相色谱检测方法相比，析出速率提高了1000倍。观察到的速率没有立即对激发光照射作出响应。当打开灯时，光催化剂膜是无活性的，并在几秒钟内被光激活。提出了先吸收被吸收的光子以填充SrTiO ₃表面的陷阱态，然后使后者吸收稳定的O ₂逸出。当激发光停止时，O ₂进化速度在几秒钟内呈指数下降。本文演示的微电极方法将有助于理解液-固界面处的许多其他反应动力学。