Uniquely designed surface nanocracks for highly efficient and ultra-stable graphite felt electrode for vanadium redox flow battery

Abstract

Large-scale activation of graphite felt electrode through a simple and cost-effective method is an imperative need for application of vanadium redox flow battery (VRFB). Here we report a rapid and low-cost method to develop highly functionalized activated graphite felt with uniformly distributed surface nanocracks (⁓30 nm × ⁓100 nm). Surface area, size, and distribution of surface nanocracks on electrode were controlled by tuning the process conditions and superior functionality was achieved through nitrogen doping. The activated graphite electrode with highly functionalized surface nanocracks offers improved pathways for electrolyte flow and improved hydrophilicity with high specific surface area (⁓19 m2g−1) for efficient vanadium redox reactions. The VRFB having activated graphite felt and nitrogen-doped alkaline graphite felt yield energy efficiencies as high as 89.6% and 87.4% at 50 mA cm−2, which is 18.3% and 15.4% higher than untreated graphite felt, respectively. Moreover, the VRFBs having activated graphite felt and nitrogen-doped activated graphite felt provide electrolyte utilization of 82.41% and 91.12% at 50 mA cm−2, 91.51% and 111.7% higher than that with untreated graphite felt. Additionally, the VRFBs were able to perform charge-discharge even at high current density of 200 mA cm−2 with electrolyte utilization of 41.78% and 61.09%, respectively.