Self-Assembled Blossom-Shaped NiCo₂S₄ Nanosheets In Situ Deposited Electrodes: Possessing High Reactivity and Selectivity for Bromine-Based Flow Batteries

Bromine-based flow batteries (Br-FBs) are emerging rapidly due to their high energy density and wide potential window for renewable energy storage systems. Nevertheless, the sluggish kinetics of the Br₂/Br^- reaction on the electrode is considered to be the main challenge contributing to the poor performance of Br-FBs. Herein, we report self-assembled blossom-shaped NiCo₂S₄ nanosheets, enabling in situ growth on graphite felt (GF) via a one-step hydrothermal method. In the prepared NiCo₂S₄-GF, the gaps formed by the nanosheets restrict bromine diffusion, the sulfuretted blossom-shaped structure provides active sites with bromine adsorption capacity, and the synergistic effect of Ni and Co accelerates the electron transfer rate, which allow the electrode to exhibit excellent electrocatalytic activity compared to commercial GF, CoS-GF, and NiS-GF. Moreover, NiCo₂S₄-GF demonstrates unique selectivity for enhancing the Br₂/Br^- redox reaction compared to the bimetallic oxide of NiCo₂O₄-GF. Consequently, the zinc-bromine flow battery (ZBFB) with NiCo₂S₄-GF achieves an energy efficiency of 80.16%, which is 16.18% higher than that of the battery with commercialized GF at a current density of 60 mA cm^-2, as well as a maximum power density of 260.75 mW cm^-2 at 280 mA cm^-2. The effective enhancement of the performance of ZBFB suggests that NiCo₂S₄-GF possesses great application potential in Br-FBs.