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

Abstract

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.