A novel high-performance all-liquid formic acid redox fuel cell: simultaneously generating electricity and restoring the capacity of flow batteries

Abstract

Conventional formic acid fuel cells rely on the oxygen reduction reaction (ORR) to generate the cathode potential. However, this approach is plagued by mixed-potential issues caused by formic acid crossover and poor cathodic electrochemical kinetics. To address these limitations, we propose an innovative design that replaces the oxygen with a liquid redox couple. By implementing the Bi-modified Pt/C electrocatalyst that can facilitate the formic acid oxidation reaction with robust CO tolerance, this novel redox fuel cell achieves an open circuit voltage and a peak power density of 1.23 V and 281.5 mW cm⁻², respectively, representing a 55.7% and 235.1% improvement over the cell with the ORR cathode. Such performance metrics are among the highest recorded for formic acid fuel cells. Density functional theory calculations and a mathematical model are utilized to describe the increased activity of the produced catalysts and the cell working principles. Moreover, the redox fuel cell can be used to restore the capacity of flow batteries by using the degraded electrolyte as a cathode fuel. For example, the capacity of vanadium redox flow batteries can be recovered to 97.6% of the initial highest level after 400 cycle tests. Exhibiting high safety and convenience, this innovative cell offers a feasible, economically viable avenue for significantly extending the flow batteries’ cycle life.