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

Abstract

After comparing the catalytic performance of three manganese-containing polyoxometalates, NaK-Mn4 and Co 3 O 4 were selected to construct the composite film, and their photoelectrocatalytic water oxidation performance was studied. • The electrocatalytic OEC performance of three Mn POM in different valence states were compared. • The composite films were successfully constructed and showed a synergistic enhancement effect on electrocatalytic OEC. • The composite film displays high PEC OEC owing to the presence of Mn-POM. In this work, three Mn-containing silicotungstates were prepared according to the published procedures, Na 2.5 K 4.5 [Mn Ⅱ 3 (OH) 3 (H 2 O) 3 (A-α-SiW 9 O 34 )]·15H 2 O (NaK-Mn3), K 4 [Mn III 3 (OH) 3 (H 2 O) 3 (A-α-SiW 9 O 34 )]·10H 2 O (K-Mn3) and Na 3.5 K 2.5 [Mn III 3 Mn IV O 3 (CH 3 COO) 3 (A-α-SiW 9 O 34 )]·20H 2 O·NaCH 3 COO·0.5KCH 3 COO (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 Co 3 O 4 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 Co 3 O 4 as a photocatalyst, the photoelectrocatalytic performance of the composite film [Mn4/Co 3 O 4 ] towards the water oxidation was investigated. The results indicate that the designed composite film shows enhanced catalytic activity for the water oxidation.