Photochemical Water Splitting at Soft Interfaces

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Although significant progress was made over the last years in the performance of visible light photocatalysts for direct water splitting, durability and turn over numbers must be improved to reach applications and the combination of the dioxygen and the dihydrogen generating steps remains a challenge. Molecular photocatalysts for water splitting typically consist of several components. We proposed the co-embedding of photoactive amphiphilic components into membrane structures at the water-lipid interface allowing facile assembly of two dimensional arrays of multi-component catalyst systems. The close proximity and the high local concentration of the catalyst subunits at the interface increase the photocatalytic performance. Simple variation of the composition of the embed¬ded dyes, catalysts and membrane amphiphiles allows the rapid optimization of the multi component catalysts. Depending on the nature of the applied amphiphiles the spatial distribution of compounds at the interface can be influenced leading to catalyst patches of high activity. Due to the dynamic nature of the assemblies self-repair of the aggregates should lead to a prolonged stability of the photocatalysts.The Chinese applicants have developed metal complex based multi-component catalysts for visible light driven water oxidation and hydrogen generation. The catalysts belong to the best performing systems currently known. The German group has experience in membrane embedding of metal complexes and the use of organic dyes as photosensitizers. The ideally complementary expertise will be combined to develop functionalized vesicles and membranes with embedded multi-component photocatalysts and the optimization of their performance. An already completed joint initial study revealed that such functionalized vesicles show photocatalytic water oxidation using blue light and exceed the performance of the components in homogeneous solution. Part of the metal complex photocatalysts will be replaced by redox active organic dyes to reduce the overall metal content of the system. Hydrogen generating catalysts will be co-embedded to obtain membranes performing simultaneous oxygen and hydrogen generation. Functionalized vesicles will be investigated and optimized in homogeneous solution, and then transferred onto surfaces or processed using printing technology. This will allow the facile preparation of complex multi-component photoactive devices with hierarchical architecture. Knowledge transfer and intensive collaboration within the project is ensured by exchange of PhD students and postdocs between the participating groups and an annual joint workshop of the groups.