Redox-targeting catalyst developing new reaction path for high-power zinc-bromine flow batteries

Zinc-bromine flow batteries (ZBFBs) are considered as one of the most promising energy storage technologies, owing to the high energy density and low cost. However, the sluggish electrochemical kinetics and severe self-discharge lead to the limited power density and service life, hindering the practical application of ZBFBs. Herein, Prussian blue modified nitrogen-doped carbon (PB@NC) is synthesized as an auxiliary redox-targeting catalyst for the bromine cathode. The excellent conductivity and adsorption capability of nitrogen-doped carbon (NC) ensure the smooth electron transfer and the enriched bromine species at the reaction interface. Under the assistance of NC, Prussian blue (PB) could rapidly lose or gain electrons, then transform into the oxidized or reduced states that subsequently engages in the targeted redox reactions with the contacted Br‐ or Br2. It offers an alternative reaction pathway for the bromine redox, promoting the electrochemical kinetics significantly, which demonstrates a reversible redox-targeting catalytic effect. Therefore, a ZBFB modified with PB@NC achieves an energy efficiency of 85.9% at a current density of 80 mA cm−2, and ultra-high energy efficiency of 71.1% even at current density of 160 mA cm−2. This work offers a promising strategy for advancing the development of ZBFBs by the efficient cathode material design.