Can electrospun nanofibres replace traditional carbon felt electrodes in redox flow batteries?

Electrospinning is fast finding its way as one of the preferred manufacturing techniques to process advanced materials for energy-storage applications. This is due to its remarkable advantages in terms of high versatility to produce free-standing nanofibre materials with controlled composition, porous microstructure and thickness. Among the different devices that can benefit from this technique, redox flow batteries are an emerging grid-scale energy- storage technology that uses electrodes consisting of commercially available carbon felts, cloths or papers. These materials exhibit relatively good stability and low cost. However, their activity towards relevant redox reactions is often poor, which leads to low-power densities and voltage efficiencies. Attempts to improve the electrochemical activity via thermal treatment or deposition of electrocatalytic species have produced mixed results. In addition, the microstructure and void volume are key properties that need optimisation to achieve effective mass transport. The electrodes act as porous media, providing heterogeneous interaction between the electrolyte and exposed catalytic sites. Therefore, the ability to control properties such as porous volume, specific surface area and tortuosity is highly desirable to minimise transport-limited inefficiencies and parasitic pumping losses. This opinion paper explores the potential of electrospun carbon materials to replace commercial carbons as electrodes for redox flow batteries, examining advantages, disadvantages and challenges.