Multi-dimensional Bi@C electrocatalyst for Cr3+/Cr2+ redox reaction boosting high-performance iron-chromium flow batteries

With the increasing demand for energy storage technology, iron-chromium flow batteries (ICFBs) have been widely concerned because of their price advantage. However, the low electrochemical activity of Cr 3+ /Cr 2+ redox couples and the side hydrogen evolution reaction limit the industrial application of ICFBs. A multi-dimensional Bi/carbon composite electrocatalyst (Bi@C) for ICFB is designed and prepared to improve the electrochemical activity of Cr 3+ /Cr 2+ redox couples. Benefiting by using the Bimetal organic framework (Bi-MOF) with solid matrix as precursors, Bi nanospheres are highly dispersed on the Bi@C electrocatalyst that effectively enhances the electrochemical activity. The special morphology of Bi@C electrocatalyst helps the transfer of electrons and ions, significantly reducing the polarization of battery. Herein, the 3D porous carbon frames accelerate mass transfer, and the 2D carbon nanobelts and carbon layer coating on 0D Bi nanospheres improve the conductivity of Bi nanospheres. Therefore, the ICFB with multi-dimensional Bi@C electrocatalyst exhibits coulombic efficiency of 98.10% and energy efficiency of 79.14% at 140 mA cm −2 , which is higher than ICFBs with commercial graphite carbon electrocatalyst and with heat treatment carbon felt. This work provides a simple and economical method to fabricate a high-performance multidimensional Bi@C electrocatalyst for Cr 3+ /Cr 2+ redox couples, boosting the development of ICFBs.