Development of high−performance and ultra−stability hierarchical nested−network−pore carbon electrode for vanadium redox flow batteries

Although graphite felt is a porous electrode in vanadium redox flow batteries, its poor specific surface area results in unfavorable reaction dynamics. Herein, we adopted self−growth zeolitic imidazolate framework−67 with N,N−dimethylformamide as a solvent (D−ZIF−67), to obtain modified graphite felts (D−EGF), which underwent oxidative etching using D−ZIF−67 as a precursor. It is found that D−EGF possesses a unique oxygen atom doped hierarchical nested−network−pore structure (macropore−mesopore−micropore). Mesopores act as a “bridge” between micropores and macropores for facilitating species diffusion and forming rich active cites, and micropores provide functional groups for electrochemical reactions. Due to the unique structure, D−EGF supplied an outstanding performance with energy efficiencies of about 83 % and 70 % at 200 and 400 mA cm⁻², respectively, and a long−life stability over 1000−cycle−test with an energy efficiency around 80 % at 200 mA cm⁻². It is shown that D−EGF is in the first tier of electrolyte utilization efficiency compared with other literatures. Furthermore, the modification method in this work provides crucial insights into the reduction of the commercial cost of vanadium redox flow battery system.