Reaction Kinetics and Mass Transfer Synergistically Enhanced Electrodes for High-Performance Zinc–Bromine Flow Batteries
Jiayi Li, Zeyu Xu, Maochun Wu
Abstract
High Resolution Image Download MS PowerPoint Slide Zinc–bromine flow batteries (ZBFBs) hold great promise for grid-scale energy storage owing to their high theoretical energy density and cost-effectiveness. However, conventional ZBFBs suffer from inhomogeneous zinc deposition and sluggish Br 2 /Br – redox kinetics, resulting in a short cycle life and low power density. Herein, a multiscale porous electrode with abundant nitrogen-containing functional groups is developed by growing zeolitic imidazolate framework-8 in situ on graphite felts, followed by a facile carbonization process to simultaneously tackle both the challenges. Theoretical and experimental results reveal that nitrogen-containing functional groups exhibit a high adsorption energy toward zinc atoms, while the microstructures promote pore-level mass transport, thereby resulting in compact and uniform zinc deposition. In the meantime, the electrode boosts the Br 2 /Br – reaction kinetics due to its high catalytic activity and large surface area. As a result, the ZBFBs equipped with optimized electrodes at both negative and positive sides can operate at an ultrahigh current density of 250 mA cm –2 while maintaining an energy efficiency of 68.0%, far surpassing that with pristine graphite felts (50.7%). Remarkably, the battery exhibits excellent cycling stability over 2000 cycles without obvious decay. This study provides a simple yet effective method for developing high-performance electrodes to tackle the critical challenges in ZBFBs, thereby promoting the commercialization of this promising energy storage technology.