Manganese‐Substituted Polyoxometalate as an Effective Shuttle Redox Mediator in Z‐Scheme Water Splitting under Visible Light

In the present study, a polyoxometalate is for the first time applied as a shuttle redox in two‐step (Z‐Scheme) photocatalytic water splitting. Photocatalytic H 2 evolution using a Mn‐substituted polyoxometalate [SiW 11 O 39 Mn II (H 2 O)] 6− as an electron donor proceeded over a Ru‐loaded SrTiO 3 :Rh photocatalyst under visible light with relatively high selectivity, accompanied by the stoichiometric production of its oxidized form [SiW 11 O 39 Mn III (H 2 O)] 5− . Photocatalytic O 2 evolution using the oxidized [SiW 11 O 39 Mn III (H 2 O)] 5− as an electron acceptor proceeded over PtO x ‐loaded WO 3 photocatalyst under visible light with relatively high quantum efficiency and selectivity, whereas the loading of effective PtO x cocatalyst was necessary to facilitate the reduction of polyoxometalate. Finally, a two‐step water splitting into H 2 and O 2 was demonstrated under visible light using the couple of Mn‐substituted polyoxometalate as shuttle redox between Ru/SrTiO 3 :Rh and PtO x /WO 3 photocatalysts, under mildly acidic conditions with pH≈4.5.