Highly Robust and Efficient Water Oxidation Catalysts based on Nanoscopic Metal Oxide Species (Polyoxometalates): from Fundamental Science to Devices

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In this SPP, photoelectrolytic cells are developed that harvest sunlight and use that energy to split water. The water splitting occurs in two half-reactions, the hydrogen and the oxygen evolution reactions (HER and OER). Only 1.23 eV per electron process are necessary to split water, highly 2 efficient light-harvesting materials will deliver cell voltages of 1.8…2.5 eV, depending. As a barrier is associated to HER and OER that suppresses the reaction and considerably lowers the overall cell efficiency, it is important to develop catalysts of high selective efficiency, low cost, and without environmental issues. We propose to develop novel catalysts for the OER on the basis of polyoxometalates (POMs).The emerging class of nanoscopic POMs in the past three years revealed significant potential as water splitting catalysts. Ranging between solvated metal ions and extended metal oxide lattices, these unique metal-oxide clusters are available for incorporation and engineering of catalytic cores with varying topologies. Current literature reveals high quantum efficiency for POM based photocatalytic water oxidation systems of up to 30% in the visible light region and turnover frequencies of about 450 h-1. However we believe that even more efficient Ru-POM catalysts as well as POM water oxidation catalysts based on more abundant and affordable metals (e.g. Mn, Co, Ni) can be developed. Besides their high efficiency, POMs have several strong features, namely the clusters can operate in neutral as well as low pHs, are thermally and oxidatively stable, can incorporate cost efficient and environmentally friendly elements and they are compatible for immobilization on semiconducting surfaces.In this proposal we offer to develop highly efficient Ru POM catalysts as well as explore the potential of POMs based on the less expensive metals (Mn, Co, Ni) for driving the OER. We will synthesize and thoroughly characterize these materials, test their catalytic performance in homogeneous phase and finally deposit them to TiO2 in order to produce photoelectrocatalytic anodes. The developments are a close collaboration between experiment and theory, with four mutually interconnected theoretical and experimental research packages.