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光催化，它结合了分子催化和纳米材料的领域。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上，如二氧化钛。当光被照射时，染料被激发，光电子被转移到半导体的导带，从而实现有效的电荷分离。它们随后被转移到分子催化剂上，在那里发生放氢。在“梦幻”系统中，水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，很难与放氢相结合。此外，氧气的生产是不受欢迎的，因为它会破坏系统，在同一个电池中同时释放氢气和氧气会带来爆炸的风险，而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，牺牲电子给体，如三乙醇胺，被用来代替水氧化，以允许染料再生。然而，牺牲电子给体价格昂贵，它们的氧化会产生高度活性的自由基，从而分解催化剂。该PHD的目的是探索不同的替代方案，以替代使用牺牲试剂的有机化合物的氧化，具有更快的动力学和比氧气生产更高的价值。不同的可能方法包括直接单电子自由基底物氧化，有机自由基氧化或无机络合物氧化，或者引入氧化还原介体并偶联到另一种光催化剂上，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.