Photoelectrochemical Reduction of CD_2 using Diamond Electrode

全球变暖等环境问题是当今社会形势下非常严重的问题，而排出的二氧化碳的回收利用是非常紧迫的挑战。我们正在尝试应用电化学方法来回收二氧化碳。我们最关注使用金刚石电极的光电化学还原，并且正在开发一个可以制造有用产品（例如乙烯或酒精）的整个系统。金刚石由于其物理硬度或高导热性而被用作切割工具或散热器。现在，金刚石利用半导体行为和高导热性被认为是下一代电子器件。另一方面，我们在这项研究中利用了金刚石的半导体行为和化学稳定性，这个想法是我们原创和独特的。由于这种化学稳定性，我们无需关心电极在任何条件下的劣化。在这项研究中，金刚石电极在连续电解几天的情况下实际上非常稳定。以下列出了本研究的历年成果。1）我们利用微波等离子体CVD制备了p型金刚石半导体的自支撑薄膜电极，并对其行为进行了研究。2）我们比较了自支撑金刚石电极和带有硅衬底的金刚石电极在Xe-Hg灯照射下的光电化学行为。3）我们比较了使用金刚石薄膜电极和其他电化学、光电化学或光催化方法的光电化学CO_2还原。4）我们研究了使用金刚石电极高效光电化学还原的最佳条件。 5）考察了电极、电解液等制备的最佳条件。6）考察了金刚石电极在恶劣条件下的应用，并考察了电极在长期电解下的稳定性。

Environmental problems such as global warming are very serious problems under the recent social situation and recycling of the exhausted carbon dioxide is the very urgent challenge. We are attempting to apply electrochemical methods to the recycling of carbon dioxide. We pay most attention to photoelectrochemical reduction using Diamond electrodes, and are developing a whole system which can make the useful products, such as ethylene or alcohol. Diamond has been using as cutting implement or heat sink due to its physical hardness or high heat conductivity. Now diamond is considered as a next-generation electronic device by the use of semiconducting behavior and high heat conductivity. On the other hand, we make use of semiconducting behavior and chemical stability of the diamond in this study, and this idea is our original and unique one. Due to this chemical stability, we need not care about deterioration of the electrodes under any conditions. In this study, diamond electrodes are actually very stable under continuous electrolysis for several days. The following lists the yearly results in this study.1) We made free-standing thin film electrodes of p-type diamond semiconductor with the microwave plasma CVD, and examined the behavior.2) We compared the photoelectrochemical behavior of free-standing diamond electrodes and diamond electrodes with silicon substrate under Xe-Hg lamp illumination.3) We compared the photoelectrochemical CO_2 reduction using diamond thin film electrodes and other electrochemical, photoelectrochemical or photocatalytic method.4) We examined the optimum conditions for the photoelectrochemical reduction using diamond electrode with high efficiency and high current density.5) We examined the optimum conditions for preparation of the electrode, electrolyte, and so on.6) We examined the application of diamond electrode under severe conditions and examined the stability of the electrode under long-term electrolysis.