Advanced dual-gradient carbon nanofibers/graphite felt composite electrode for the next-generation vanadium flow battery

Vanadium flow battery (VFB) is one of the most promising energy storage technologies because of its superior safety, reliability and cycle life, but the poor electrochemical performance at high current density limits its commercial application. Herein, an advanced design of the dual-gradient carbon nanofibers/graphite felt (DG-CNFs/GF) composite electrode is firstly proposed for the next-generation VFB with high power density. Specifically, there is a macro gradient distribution of CNFs along the thickness direction of the electrode, meanwhile a micro gradient distribution of CNFs is also existed along the radial direction of a single fiber, and both the macro and micro gradient structure are verified through the physicochemical characterizations. In addition, the DG-CNFs/GF with a dual-gradient structure exhibits an excellent electrocatalytic activity and a fast mass transfer characteristic. It is worth noting that the energy conversion efficiencies, cycling stability in addition to power density of VFB with DG-CNFs/GF are much better than those with commercial GF, which make the dual-gradient DG-CNFs/GF to be a promising alternative. Most importantly, the accomplishment of this work will provide a promising development direction of the highly efficient electrode for the next-generation VFB with high power density.