Thin Films of Fully Noble Metal-Free POM@MOF for Photocatalytic Water Oxidation

P2W18Co4@MOF-545 which contains the sandwich-type polyoxometalate (POM) [(PW9O34)2Co4(H2O)2]10- (P2W18Co4) immobilized in the porphyrinic MOF-545 framework, is a “three-in-one” (porosity + light capture + catalysis) heterogeneous photosystem for the oxygen evolution reaction (OER). Thin films of this composite were synthesized on transparent and conductive indium tin oxide (ITO) supports using electrophoretic (EP) or drop casting (DC) methods, thus providing easy-to-use devices. Their electro- and photocatalytic activities for OER were investigated. Remarkably, both types of films exhibit higher turnover numbers (TONs) than the original bulk material previously studied as suspension for the photocatalytic OER, with TONs after 2 hours equal to 1600 and 403 for DC and EP films respectively compared to 70 for the suspension. This difference of catalytic activities is related to the proportion of efficiently illuminated crystallites, whereby a DC thin film offers the largest proportion of POM@MOF crystallites...