Multinuclear Metal Complex Photosensitizers Covalently-Coupled to Cobalt-based Catalysts for Hydrogen Evolution

在过去的几十年里，大量的研究集中在将太阳能转化为化学能上。在这方面，光催化过程对生产所谓的“太阳能燃料”起着至关重要的作用。氧和氢是两种重要的太阳能燃料，分别由水的催化氧化和质子的还原产生。光催化装置的两个主要组成部分是光敏剂和催化剂。最近的事态发展可能会大大提高这两个组成部分的表现。例如，多核Ru(II)多吡啶配合物作为光敏剂被用于光催化析氧反应，以增加对太阳光的吸收，并能够吸收较低能量的太阳光。然而，对于类似的析氢反应，文献中很少描述多核配合物，通常使用单核配合物。另一方面，最近出现了一类新的钴(II)多吡啶分子络合物作为析氢催化剂。事实证明，这些催化剂比其他体系更坚固，在纯水中表现出更高的电催化活性。出于这个原因，该研究计划结合了这两个光催化系统的最新发展。为了进一步提高设计体系的效率，另一个目标是光敏剂和催化剂的共价键。通过这种方法，可以避免光敏剂对催化剂的过量，并促进从光敏剂到催化剂的电子转移过程。所设计的体系在水溶液中的光催化活性应该明显高于以前报道的体系。此外，它有望提供一个高效的光催化系统，利用广泛的可见光到近红外太阳光谱。这可能会对新体系的开发产生重大影响，因为在低能光的水溶液中进行光催化仍然具有挑战性。

In the last decades, tremendous research has been focused on the conversion of solar energy into chemical energy. In this regard, photocatalytic processes play a crucial role to produce so-called “solar fuels”. Oxygen and hydrogen are two important solar fuels and can be generated by the catalytic oxidation of water and reduction of protons, respectively. The two main components of a photocatalytic device are the photosensitizer and the catalyst. Recent developments could significantly improve the performance of both components. For example, multinuclear ruthenium(II) polypyridyl complexes as photosensitizer have been employed for the photocatalytic oxygen evolution reaction to increase the sunlight absorption and they are capable to absorb lower-energetic solar light. However, multinuclear complexes are rarely described in literature for the similar hydrogen evolution reaction, usually mononuclear complexes are used. On the other hand, a new family of molecular cobalt(II) polypyridyl complexes as catalysts for hydrogen evolution has recently emerged. These catalysts proved to be more robust than other systems and display higher activities for electrocatalysis in pure water. For this reason, the research plan is a combination of these two recent developments in photocatalytic systems. To further increase efficiency of the designed systems, another aim is the covalent linkage of photosensitizer and catalyst. By this approach, the excess of photosensitizer to catalyst can be avoided and the electron-transfer process from the photosensitizer to the catalyst will be facilitated. The designed systems should possess distinctly higher photocatalytic activity in aqueous solutions than previously reported systems. Moreover, it is expected to afford an efficient photocatalytic system, which utilize a wide range of the visible to near-infrared solar spectrum. This could be a major impact for the development of new systems, because photocatalysis in aqueous solutions with low-energetic light is still challenging.