Hydrogen storage/evolution behavior of nafion/NaCl/graphene quantum dot (GQD) mixed matrix as selective hydrogen capacitor (power source) was evaluated in detail through an electrochemical process at two independent potential ranges. For this purpose, a three electrode system included Pt disk as counter electrode, Ag/AgCl as reference electrode and GQD-based mixed matrix-modified Pt disk as working electrode. For hydrogen storage, the deposition potential and time were evaluated to -1.0 V (vs. Ag/AgCl) and 120 s, respectively under high basic solution generated using NaOH (1.0 M) solution, followed by evolution of hydrogen at +0.8 V (vs. Ag/AgCl) during formation of hydrogen bubbles. The main advantage of this system was the occurrence of hydrogen storage and evolution at two independent potential windows. Both mass transfer and adsorption processes were estimated for the tensammetric peak during the evolution step. The mechanism of hydrogen storage and evolution was obeyed from diffusion and tensammetry, respectively. According to Randles-Sevcik equation using 1.0 mM Fe(CN)(6)(3-/4-), the active surface area of nafion/NaCl/GQD mixed matrix was similar to 1906 m(2)g(-1). Based on the CHN analyses, pressure concentration temperature as well as hydrogen temperature-programmed desorption, the capacity of the synthesized GQDs for hydrogen storage and evolution was estimated to at least 10.1 and 8.6 wt%, respectively. The stability of the electrode was-also estimated during 7000s by chronoamperometry during applying at least 40 cycles in the range from -1.0 to +1.3 V with reproducible tensammetric peak current (relative standard deviation: 2.54%). (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.