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 H2 evolution using a Mn‐substituted polyoxometalate [SiW11O39MnII(H2O)]6− as an electron donor proceeded over a Ru‐loaded SrTiO3:Rh photocatalyst under visible light with relatively high selectivity, accompanied by the stoichiometric production of its oxidized form [SiW11O39MnIII(H2O)]5−. Photocatalytic O2 evolution using the oxidized [SiW11O39MnIII(H2O)]5− as an electron acceptor proceeded over PtOx‐loaded WO3 photocatalyst under visible light with relatively high quantum efficiency and selectivity, whereas the loading of effective PtOx cocatalyst was necessary to facilitate the reduction of polyoxometalate. Finally, a two‐step water splitting into H2 and O2 was demonstrated under visible light using the couple of Mn‐substituted polyoxometalate as shuttle redox between Ru/SrTiO3:Rh and PtOx/WO3 photocatalysts, under mildly acidic conditions with pH≈4.5. Mn POM for Z‐Scheme: A Mn‐subsituted polyoxometalate (POM)‐based redox couple is demonstrated for the first time to function as a redox mediator in a two‐step water splitting system under visible light. Specifically, the suitable redox potential and redox reversibility of Mn in the POM framework are the key beneficial features of the present redox couple. The study demonstrates the potential of the modified POM as a stable redox shuttle mediator for two‐step water splitting systems.