This study develops a strategy to optimize the chemical state of bimetallic PtRu alloys in order to increase the catalytic activity of the PtRu alloy/RGO counter electrodes (CEs) used in efficient dye-sensitized solar cells (DSCs). The well-dispersed bimetallic Pt1-xRux (0 <= x <= 1) nanoparticles (NPs) are stabilized with RGO after co-reduction of the metal precursor ions and graphene oxide. The nanohybrids exhibit a 3D network structure of RGO with a high NP loading on the RGO surface. The NP size is in range of 1-5 nm, with an average size of 2.5 nm. X-ray diffraction spectroscopy and HAADF-STEM measurements are conducted in order to confirm the structure of the PtRu alloy/RGO nanohybrid. As a result of optimizing the nanohybrid structure for high catalytic activity toward the reduction of the triiodide ions, the Pt0.7Ru0.3 NPs/RGO nanohybrid exhibited the highest electrocatalytic activity, which corresponds to the lowest charge transfer resistance of 3.29 V, among the electrodes. The DSC fabricated with Pt0.7Ru0.3 NPs/RGO CEs exhibits increases in efficiency of 12% compared with that of the Pt/RGO-based DSC and of 24% more than the efficiency of the Pt-free device. The obtained results indicate that tailoring the electronic structure of an alloy can be used to enhance the catalytic activity of nanohybrid CEs, and in turn for the construction of high-efficiency DSCs. (C) 2016 Elsevier Ltd. All rights reserved.