InSitu Generation of Active Molybdenum Octahedral Clusters for Photocatalytic Hydrogen Production from Water

The photocatalytic hydrogen evolution reaction (HER) from water under homogeneous and heterogeneous conditions is explored for the {Mo6Br8i}(4+) cluster core based unit starting from (TBA)(2)[(Mo6Br8F6a)-F-i] (TBA=tetra-n-butylammonium; i and a refer to the face-capping inner and terminal apical ligand, respectively). The catalytic activity of {Mo6Br8i}(4+) is enhanced by the insitu generation of [(Mo6Br8F5a)-F-i(OH)(a)](2-), [(Mo6Br8F3a)-F-i(OH)(a)(3)](2-), and [Mo6Br8i(OH)(a)(6)](2-), which are identified by ESIMS, luminescence, and NMR techniques. Full substitution of F- by OH- leads to the formation of (H3O)(2)[Mo6Br8i(OH)(a)(6)]10H(2)O; its structure was determined by single-crystal XRD. The immobilization of the active {Mo6Br8i}(4+) onto graphene oxide (GO) surfaces enhances its stability under catalytic conditions. The catalytic activity of the resulting (TBA)(2)Mo6Br8i@GO material is improved with respect to GO, but is reduced compared to the activity under homogeneous conditions because of changes in the GO semiconducting properties as well as lower activity and/or accessibility of the anchored cluster.