Carbonized tubular polypyrrole with a high activity for the Br-2/Br- redox reaction in zinc-bromine flow batteries

Zinc-bromine flow batteries have been regarded as one of the most promising technologies for largescale energy storage. However, the widespread application of this technology is still hindered by its low power density, primarily resulting from a large polarization in the Br-2/Br- electrode. In this work, carbonized tubular polypyrrole with abundant nitrogen- and oxygen-containing functional groups is synthesized and, for the first time, applied to a zinc-bromine flow battery as a positive electrode material. Experimental results unravel that carbonized tubular polypyrrole exhibits a high activity toward the Br-2/Br- redox reaction, and enables the zinc-bromine flow battery to be operated at a current density of 80 mA cm(-2) with a high energy efficiency of 76.0%. In contrast, the battery with the pristine graphite felt electrode can only output an energy efficiency of 69.4% at the same current density. In addition, no degradation is observed for the zinc-bromine flow battery equipped with carbonized tubular polypyrrole for 100 cycles. These superior results suggest that carbonized tubular polypyrrole is a promising positive electrode material for zinc-bromine flow batteries. (C) 2018 Elsevier Ltd. All rights reserved.