Graphene-based RuO2 nanohybrid as a highly efficient catalyst for triiodide reduction in dye-sensitized solar cells

This study is the first to report the synthesis of graphene-based RuO2 nanohybrid materials and their application as a counter electrode (CE) in dye-sensitized solar cells (DSCs). Ru nanoparticles (RuNPs) with an average size of 9 nm were uniformly immobilized on the surface of reduced graphene oxide (RGO) with the simultaneous co-reduction of Ru precursor ions and graphene oxide (GO) to Ru atoms and RGO, respectively, through dry plasma reduction (DPR) under atmospheric pressure and at near room temperature without using any toxic chemicals. Since RuNPs are more susceptible to oxidation, Ru atoms located on the surface of RuNPs are further oxidized to RuO2 in atmosphere. The resulting RuO2-RGO nanohybrid with a very small amount of Ru exhibits low charge transfer resistance, low diffusion impedance and good long-term stability. The application of RuO2-RGO nanohybrid as an alternative CE for DSCs leads to high energy conversion efficiency of 8.32 ± 0.15%, which is comparable to the value of 8.16 ± 0.13% of DSCs based on a Pt-NP CE prepared by DPR. This study also discusses the influence of hydrogen species existing in either precursor ions or graphenes on the formation of uniform and well-dispersed NPs on the substrates.