Topics in Current Chemistry Volume 303, 2011, pp 121-150
Date: 06 May 2011

Artificial Photosynthesis Challenges: Water Oxidation at Nanostructured Interfaces

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Innovative oxygen evolving catalysts, taken from the pool of nanosized, water soluble, molecular metal oxides, the so-called polyoxometalates (POMs), represent an extraordinary opportunity in the field of artificial photosynthesis. These catalysts possess a highly robust, totally inorganic structure, and can provide a unique mimicry of the oxygen evolving center in photosynthetic II enzymes. As a result POMs can effect H2O oxidation to O2 with unprecedented efficiency. In particular, the tetra-ruthenium based POM [RuIV 4(μ-OH)2(μ-O)4(H2O)4(γ-SiW10O36)2]10−, Ru 4 (POM), displays fast kinetics, electrocatalytic activity powered by carbon nanotubes and exceptionally light-driven performance. A broad perspective is presented herein by addressing the recent progress in the field of metal-oxide nano-clusters as water oxidation catalysts, including colloidal species. Moreover, the shaping of the catalyst environment plays a fundamental role by alleviating the catalyst fatigue and stabilizing competent intermediates, thus responding to what are the formidable thermodynamic and kinetic challenges of water splitting. The design of nano-interfaces with specifically tailored carbon nanostructures and/or polymeric scaffolds opens a vast scenario for tuning electron/proton transfer mechanisms. Therefore innovation is envisaged based on the molecular modification of the hybrid photocatalytic center and of its environment.