Core-shell Ni/NiO heterostructures as catalytic cathodes enabling high-performance zinc bromine flow batteries

Zinc bromine flow batteries (ZBFBs) are well suited for stationary energy storage due to their attractive features of high energy density and low cost. Nevertheless, the ZBFBs suffer from low power density and limited efficiency owing to the relatively severe polarization of the Br₂/Br⁻ redox couple. Herein, a three-dimensional (3D) hierarchical composite electrode based on core-shell Ni/NiO heterostructures anchored on graphite felt (Ni/NiO@GF) is designed to promote the kinetics of the Br₂/Br⁻ couple, so as to improve the power density and efficiency of the ZBFB. In this design, the highly conductive carbon felt and Ni cores provide a composite electrode with a 3D electron transporting framework to guarantee excellent electronic conductivity, while the NiO shells possess great absorption ability to Br₂ and brilliant catalytic activity for the Br₂/Br⁻ redox reaction to reduce the electrochemical polarization. As a result, an enhanced ZBFB with Ni/NiO@GF electrode shows an outstanding energy efficiency of 86% at 20 mA cm⁻² and can be operated at a current density of up to 160 mA cm⁻² with a respectable energy efficiency of 67%. These results exhibit a promising strategy to fabricate catalytic electrodes for high-performance ZBFBs.