Iron–Chromium Flow Battery

The Fe–Cr flow battery (ICFB), which is regarded as the first generation of real FB, employs widely available and cost-effective chromium and iron chlorides (CrCl₃/CrCl₂and FeCl₂/FeCl₃) as electrochemically active redox couples. ICFB was initiated and extensively investigated by the National Aeronautics and Space Administration (NASA, USA) and Mitsui Group (Japan) between the 1970s and 1980s. From the past few decades to now, extensive investigations on the ICFB systems have been conducted. Moreover, due to the capital cost of ICFBs being much lower than that of all-vanadium FBs (VFBs) and zinc-based FBs (ZFBs) in theory, they have been seen as promising direction that possess a huge potential for large-scale promotion. With the issues of electrolyte intermixing, self-discharge phenomenon, permeation through the membrane/separator, and hydrogen evolution to be tackled, ICFB techniques will move further out of the labs and are expected to realize industrialization requirements such as high stability and high power rate. This chapter summarizes the research history, research progress of pivotal components (catholyte/anolyte, carbon electrodes, and separators), and development process of ICFBs, to provide concise guidance for researchers in the related fields.