Coupling Hydrogen Evolution to Clean and Sustainable Oxidations in Dye-Sensitised Photocatalysis

太阳能燃料的圣杯是利用太阳能将水分解成氢和氧的能力。最新的方法之一是染料敏化的纳米材料，它结合了分子催化和纳米材料领域。在这种方法中，分子染料和催化剂被固定在半导体纳米颗粒如二氧化钛上。当光照射时，染料被激发，光电子被转移到半导体的导带，导致有效的电荷分离。它们随后被转移到分子催化剂上，在那里发生析氢。在“梦”系统中，水的氧化将允许染料的再生。然而，水氧化是一个动力学缓慢的过程，这是难以耦合到析氢。此外，氧气的产生是不希望的，因为它损害系统，在同一电池中氢气和氧气的释放引入爆炸的风险，并且氧气本身几乎没有市场价值。到目前为止，为了研究氢半反应，使用三乙醇胺等牺牲电子给体作为水氧化的替代品，以实现染料再生。然而，牺牲电子供体是昂贵的，并且它们的氧化产生分解催化剂的高反应性自由基。该博士学位的目的是探索不同的替代方案，以取代使用牺牲试剂来氧化有机化合物，其动力学速度更快，价值比氧气生产更高。不同的可能方法可能包括直接单电子自由基底物氧化，通过有机自由基或无机复合物氧化，或引入氧化还原介体并与另一种光催化剂偶联，形成Z-方案。

The holy grail of solar fuels is the ability to use solar energy to split water into its elements: hydrogen and oxygen. One of the newest approaches is dye sensitised photocatalysis which combines the fields of molecular catalysis and nanomaterials. In this approach, molecular dyes and catalysts are immobilised on a semiconductor nanoparticle such as titanium dioxide. When light is irradiated, the dye is excited and the photoelectrons are transferred to the conduction band of the semiconductor leading to efficient charge separation. They are later transferred to the molecular catalyst, where hydrogen evolution occurs. In a 'dream' system, water oxidation would allow for the regeneration of the dye. However, water oxidation is a kinetically slow process which is difficult to couple to hydrogen evolution. Furthermore, the production of oxygen is undesired as it damages the system, evolution of both hydrogen and oxygen in the same cell introduces a risk of explosion and oxygen itself has little market value. Until now, to study the hydrogen half reaction, sacrificial electron donors such triethanolamine are used as a substitute for water oxidation to allow for dye regeneration. However, sacrificial electron donors are expensive and their oxidation produces highly reactive radicals which decompose the catalyst. The aim of this PhD is to explore different alternatives to substitute the use of sacrificial reagents for an oxidation of an organic compound with faster kinetics and higher value than oxygen production. Different possible approaches might include direct one-electron radical substrate oxidation, oxidation by an organic radical or inorganic complex, or introduction of a redox mediator and coupling to another photocatalyst, forming a Z-scheme.