Carbon layer-exfoliated, wettability-enhanced, SO3H-functionalized carbon paper: A superior positive electrode for vanadium redox flow battery

In this paper, carbon paper as positive electrode for vanadium redox flow battery was etched by chlorosulfonic acid with assistance of ultrasonication. Carbon layer-exfoliated, wettability-enhanced, SO3H-functionalized carbon paper was successfully achieved by facile treatment. The electrochemical kinetics of VO2+/VO2+ redox reaction on carbon paper was significantly improved after the treatment. Carbon paper after ultrasonication-assisted treatment exhibits better electrochemical activity compared with the untreated and only-soaking samples. The cell using treated carbon paper as positive electrode shows larger discharge capacity and higher energy efficiency compared with the pristine cell. The initial discharge capacity of the cell using optimal treated carbon paper reaches 127.7 mA h, 20.8 mA h larger than that of the pristine one at 50 mA cm(-2). Furthermore, the average energy efficiency increases by 5.1% by using the treated electrode. The introduced sulfonic groups as active sites and increased surface area by etching can reduce the electrochemical polarization of VO2+/VO2+ redox reaction. Moreover, the improved wettability of treated carbon paper can accelerate mass transfer of active species. Therefore, the reduced electrochemical polarization and accelerated mass transfer of active species conjointly cause the enhanced electrochemical properties of the treated carbon paper. (C) 2017 Elsevier Ltd. All rights reserved.