Fabrication of highly effective electrodes for iron chromium redox flow battery

Iron-chromium redox flow batteries (ICRFBs) have emerged as promising energy storage devices due to their safety, environmental protection, and reliable performance. The carbon cloth (CC), often used in ICRFBs as the electrode, provides a suitable platform for electrochemical processes owing to its high surface area and interconnected porous structure. However, the CC electrodes have issues, such as, insufficient electron transfer performance, which limits their industrial application. Here, we employed silicic acid etching to carve dense nano-porous structures on the surface of CC electrodes based on the favorable design of ICRFBs and the fundamental principles of electrode polarization losses. As a result, we developed a multifunctional carbon cloth electrode with abundant vacancies, notably enhancing the performance of the battery. The fabricated electrode showcased a wealth of defect sites and superior electronic transport properties, offering an extensive and effective reaction area for rapidly flowing electrolytes. With an electrode compression ratio of 40% and the highest current density in ICRFBs so far (140 mA·cm−2), the battery achieved the average energy efficiency of 81.3%, 11.24% enhancement over the previously published work. Furthermore, throughout 100 charge–discharge cycles, the average energy efficiency degradation was negligible (∼ 0.04%), which has the potential to become the most promising candidate for large-scale and long-term electrochemical energy storage applications.