Flexible all-solid-state supercapacitors (SCs) are fabricated using graphene/carbon black nanoparticle (GCB) film electrodes and cross-linked poly(vinyl alcohol)-H2SO4 porous gel electrolytes (gPVAP -H2SO4). The GCB composite films, with carbon black (CB) nanoparticles uniformly distributed in the graphene nanosheets, greatly improve the active surface areas and ion transportation of pristine graphene film. The porous structure of as-prepared gPVAP-H2SO4 membrane improves the equilibrium swelling ratio in electrolyte and provides interconnected ion transport channels. The chemical cross-linking solves the fluidity problem of PVA-H2SO4 gel electrolyte at high temperature. As-fabricated GCB//gPVAP(20)-H2SO4//GCB flexible SC displays an increased specific capacitance (144.5 F g(-1) at 0.5 A g(-1)) and a higher specific capacitance retention (67.9% from 0.2 to 4 A g(-1)). More importantly, the flexible SC possesses good electrochemical performance at high temperature (capacitance retention of 78.3% after 1000 cycles at 70 degrees C). (C) 2014 Elsevier B.V. All rights reserved.