Regulated adsorption capability by Interface–Electric–Field enabling promoted electrochemical kinetics of Zinc–Bromine flow batteries

Abstract

Zinc–bromine flow batteries (ZBFB) are gaining significant attention for large–scale energy storage due to the high energy density and affordable cost. Nevertheless, the diffusion of Br2 and the relatively low activity of Br2/Br− impede their broader application. Herein, a bi–phasic rutile/anatase–TiO2 embedded in carbon composite with hollow sphere structure (R/A–TiO2@HCS) is proposed as the catalyst for the Br2/Br− electrode. The internal electric field (IEF) formed between rutile–TiO2 and anatase–TiO2 regulates the adsorption capability for active bromine species. The appropriate adsorption capability can rapidly transfer the generated Br2 complex (QBrn) to the adsorbent component R/A–TiO2 during charging, liberating the carbon active sites, and release QBrn back to the carbon reaction sites timely during discharging, satisfying the both adsorption and desorption requirements of QBrn in different processes. The kinetics for oxidation and reduction are simultaneously enhanced. Moreover, the hollow construction offers storage space for QBrn, relieving its penetration problem. Under the synergistical cooperation, the ZBFB assembled with R/A–TiO2@HCS demonstrates the energy efficiency (EE) of 83.6 % at 80 mA cm−2, without significant decay over 500 cycles. And the EE still maintains 70.0 % even under 160 mA cm−2. This work highlights the significance of tailored electrocatalyst for ZBFB.