Preparation and characterization of KOH-treated electrospun nanofiber mats as electrodes for iron-based redox-flow batteries

A series of electrospun nanofiber mats have been fabricated from polyacrylonitrile (PAN) precursor, followed by treatments with pyrolytic heat and KOH solutions. The heat & KOH-treated electrospun nanofiber mats were investigated to serve as electrodes for iron-based redox-flow batteries (RFBs). The morphology, porosity, wettability, and cyclic voltammetry have been studied for the treated electrospun nanofiber mats. The KOH treatment effectively reduced the fiber diameter, increased the mat porosity, and enhanced the surface wettability. Specifically, the heat & 4M KOH-treated electrospun nanofiber mat has similar to 300 nm of fiber diameter, 92% of porosity, and 20 degrees of contact angle. Compared with the electrospun nanofiber mat treated with heat alone, the heat & 4M KOH-treated electrospun mat increases the anodic peak current in cyclic voltammogram of Fe3+/Fe2+ redox by 60% at the same scan rate, implying considerably increased specific surface area. The KOH treatment does not seem to change the peak separation: around 120 mV is observed at 10 mV/s of scan rate on all electrospun nanofiber mats, regardless of treatment with heat alone or heat & KOH solutions. Such peak separation of those electrospun nanofiber mats is substantially narrower than that of a commercial carbon felt (977 mV at 3 mV/s), indicating much improved redox activity. The narrow peak separation and reasonably high current suggest that the treated electrospun nanofiber mats are promising candidates as electrodes for iron-based RFBs and other aqueous batteries.