Charge-Separated States in Immobilized H2-Evolving Ru-Pt Photocatalyst Stabilized by Electric Field Modulation
in: Temporal Proceedings (2019)
Dye-sensitized H2-evolving photocathodes render the alternative and promising way for solar energy-based fuels generation. However, critical issues have been encountered to achieve high-performance dye-sensitized photocathodes due to, for example, the desorption photocatalyst and short-lived charge separated states . Recently, efforts to enhance the performance of dye-sensitized photocathodes are undertaken by structural modification of the catalysts , surface passivation , and external stimuli by applying external bias .
In this work, we investigate the dynamic of light-induced charge transfer, i.e., the hole injection and charge separation, in immobilized [RuII(bpyMeP)2tpphzPtCl2]2+ or Ru-Pt on NiO cathodes by using transient absorption spectroscopy. Particularly, we study the effect of surface passivation by atomic deposition of Al2O3 and the effect of different electric field modulation on the hole injection and stability of charge-separated states (CSS). The performance of Ru-Pt – sensitized NiO is, in principle, substantially controlled by the stability of h+(NiO)|bpy•¯- and h+(NiO)|tpphz•¯-based CSS. The present results show that Al2O3 passivation on the NiO|RuPt surface stabilizes the CSS by suppressing the recombination reaction resulting in a longer-lived CSS of 20 ns (vs. 2.5 ns in non-passivated NiO). The modulation of an electric field by applying reverse (negative) bias on the photocathode stabilizes the h+(NiO)/tpphz•¯ CSS due to suppressed non-geminate holes as recombination center on NiO surface. Furthermore, we report evidence of Coulombic repulsion force which shifts bpy•– toward tpphz ligand resulting in stabilized h+(NiO)|tpphz•– CSS with a lifetime of up to 39 ± 4 ns.