0 In this study, the concentration effects of sulfuric acid solution and V(V) on positive electrolyte component of vanadium redox batteries were investigated by cyclic voltammetry and electrochemical impedance spectroscopy with pencil graphite working electrode for the first time. The current and redox capacity values of the oxidation and reduction peaks were determined by cyclic voltammetry. The optimum scanning rate and sulfuric acid concentration were at 20 mV s(-1) and 5.0 M, respectively. The current and capacity values of the anodic and cathodic peaks were found to increase but the charge transfer resistance decreased with increasing sulfuric acid concentration. When the concentration of V(V) was increased from 0.04 M to 2.0 M, the current and capacity values of the anodic and cathodic peaks increased. The charge transfer resistance also decreased with increasing the concentration of V(V), as expected. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.