ZIF-derived holey electrode with enhanced mass transfer and N-rich catalytic sites for high-power and long-life vanadium flow batteries

Electrode materials with good redox kinetics, excellent mass transfer characteristics and ultra-high stability play a crucial role in reducing the life-cycle cost and prolonging the maintenance-free time of the vanadium flow batteries (VFB). Herein, a nitrogen-doped porous graphite felt electrode (N-PGF) is proposed by growing ZIF-67 nanoparticles on carbon fibers and then calcinating and acid etching. The multi-scale structure of carbon fiber gap (electrolyte flow), micro/nano pore (active species diffusion) and Nitrogen active center (reaction site) in N-PGF electrode effectively increases the catalytic sites and promotes mass transfer characteristics. Reasonable electrode design makes the battery show excellent rate performance and ultra-high cycling stability. The peak power density of the battery reaches 1006 mW cm-2. During 1000 cycles at 150 mA cm-2, the average discharge capacity and average discharge energy of N-PGF increase substantially by 11.6% and 23.4% compared with the benchmark thermal activated graphite felt, respectively. More excitingly, after ultra-long term (5000 cycles) operation at an ultra-high current density (300 mA cm-2), N-PGF exhibits an unprecedented energy efficiency retention (99.79%) and electrochemical performance stability.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

A nitrogen-doped porous graphite felt electrode is proposed to improve the performance of vanadium flow batteries by increasing catalytic sites and promoting mass transfer characteristics. Experimental results show that the electrode exhibits excellent rate performance and ultra-high cycling stability.