Facile multilayer assemble of a mixed-valence Mn4-containing silicotungstate and its electrochemical study with Co3O4 as co-catalyst for photoelectrocatalytic water oxidation

Abstract In this work, three Mn-containing silicotungstates were prepared according to the published procedures, Na2.5K4.5[MnⅡ3(OH)3(H2O)3(A-α-SiW9O34)]·15H2O (NaK-Mn3), K4[MnIII3(OH)3(H2O)3 (A-α-SiW9O34)]·10H2O (K-Mn3) and Na3.5K2.5[MnIII3MnIVO3(CH3COO)3 (A-α-SiW9O34)]·20H2O·NaCH3COO·0.5KCH3COO (NaK-Mn4), and then their electrochemical behaviors were studied at pH 5 and electrocatalytic activities for water oxidation were compared at pH 7. Furthermore, the compound NaK-Mn4, which displayed the best catalytic activity for the water oxidation among three silicotungstates, is chosen to construct the composite films using PDDA (PDDA: poly(diallyldimethylammonium chloride)) or Co3O4 components through layer-by-layer (LbL) method and the fabricated composite films were proved by measuring cyclic voltammogram (CV) curves and UV–visible spectra. Additionally, taking the advantage of Co3O4 as a photocatalyst, the photoelectrocatalytic performance of the composite film [Mn4/Co3O4] towards the water oxidation was investigated. The results indicate that the designed composite film shows enhanced catalytic activity for the water oxidation.