Novel carbon electrodes for zinc–bromine batteries

Abstract

Zinc-bromine batteries have long been considered one of the most suitable storage technologies due to their potential long life, deep discharge characteristics and potential low manufacturing cost, as well as very high theoretical specific energy density (~440 Wh/kg). However, there are still a number of challenges to their commercial success, including electrode lifetime, electrochemical efficiency and cost. The major purpose of this study is to investigate the property of both zinc and bromine electrodes in zinc bromine flow batteries, and to develop new materials for zinc bromine flow battery electrodes, suitable for utility scale use. Different carbon materials and high density polyethylene-carbon composites have been evaluated through physical and electrochemical methods. Calgon activated carbon, carbon cloth, multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO) and cryogel carbon have been investigated as the electrocatalysts for the bromine/bromide redox couple reaction in the positive half-cell of the zinc bromine redox flow batteries. As for the zinc electrodes, high density polyethylene (HDPE)-carbon black (CB) and HDPE-multiwall carbon nanotubes (MWCNTs) composites have been studied with macroscopic and microscopic techniques. The MWCNTs shows the best performance of the five carbon candidates. The HDPE-CB composite electrode exhibits better zinc deposition than the HDPE-CNT composite electrode due to a lower nucleation overpotential and higher exchange current density. In addition, the interfacial structure of the electrode/electrolyte on the bromine electrode and zinc electrode in zinc bromine electrolyte has been illustrated for the first time using electrochemical impedance spectroscopy.