Anisotropy Engineering for Constructing Gradient Electrodes with High-Efficiency Bi/C Catalyst In Situ for...

Iron-chromium flow batteries (ICFBs) are regarded as one of the most potential large-scale energy storage devices. Nevertheless, the slow dynamics of the Cr³⁺/Cr²⁺ redox couples hinder the development of ICFBs. Here, a high-efficiency carbon-loaded bismuth (Bi/C) catalyst is fabricated and introduced on the electrode in situ to improve the dynamics with the assistance of polyvinylpyrrolidone (PVP). To derive the greatest value, we explore the current density anisotropy in ICFB and design a strategy of anisotropy engineering to meet the requirements of the anisotropy for catalysts. In the work, the gradient electrode (G-PBiC/TCF) with a high-efficiency Bi/C catalyst is successfully prepared. In addition, the ICFB assembled with the G-PBiC/TCF(M/m, the side of more catalysts facing the Membrane side) shows excellent battery performance. It can run over 500 cycles with EE of 81.36% at 120 mA cm^-2, which is the longest cycle life reported. Furthermore, the catalytic mechanism and the effect of the catalyst distribution on the performance are explained by the DFT calculation and multi-physical field simulation. This work provides a novel pathway to design that catalyst-supported gradient electrode with high performance and low cost.