Graphene-based RuO 2 nanohybrid as a highly efficient catalyst for triiodide reduction in dye-sensitized solar cells Van-Duong Dao a,b , Liudmila L. Larina a,c , Joong-Kee Lee b , Kwang-Deog Jung d , Bui The Huy e , Ho-Suk Choi a, * a Department of Chemical Engineering, Chungnam National University, 220 Gung-Dong, Yuseong-Gu, Daejeon 305-764, Republic of Korea b Energy Storage Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea c Department of Solar Photovoltaics, Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St. 4, 119334 Moscow, Russia d Clean Energy Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea e Department of Chemistry, Changwon National University, 220 Changwondaehak-ro, Uichang-gu, Changwon, Gyeongnam 641-773, Republic of Korea ARTICLE INFO Article history: Received 18 July 2014 Accepted 3 October 2014 Available online xxxx ABSTRACT This study is the first to report the synthesis of graphene-based RuO 2 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 precur- sor 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 RuO 2 in atmosphere. The resulting RuO 2 -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 RuO 2 -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. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Dye-sensitized solar cells (DSCs) are a promising alternative as next-generation solar cells due to their low fabrication cost and high efficiency [1]. Due to its excellent catalytic activity and high electrical conductivity, platinum (Pt) is the most commonly used material for the counter electrode (CE) of DSCs [1–6]. However, Pt is known to be an expensive material (137.00 USD/G for chloroplatinic acid hydrate, Sigma–Aldrich) with limited reserves [7]. Thus, its large-scale application is too expensive to compete with conventional solid-state photovoltaic (PV) devices. In order to introduce http://dx.doi.org/10.1016/j.carbon.2014.10.012 0008-6223/Ó 2014 Elsevier Ltd. All rights reserved. * Corresponding author. E-mail address: hchoi@cnu.ac.kr (H.-S. Choi). CARBON xxx (2014) xxx – xxx Available at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/carbon Please cite this article in press as: Dao V-D et al. Graphene-based RuO 2 nanohybrid as a highly efficient catalyst for triiodide reduction in dye- sensitized solar cells. Carbon (2014), http://dx.doi.org/10.1016/j.carbon.2014.10.012