Rde Kinetic Study of V(IV)/V(V) and V(II)/V(III) Reactions on Thermally Activated and Non-Activated Carbon Felts

Abstract

Graphite felt is the most common electrode material used at both the cathode and the anode in vanadium redox flow batteries (VRFBs). Graphite felt exhibits good activity towards the redox reactions, has a wide operational potential range, and exhibits stability in acidic environments. A variety of studies have been conducted to investigate the effects of different felt pre-treatment methods for on VRFB performance (1, 2). Basically the pre-treatment methods can be categorized into oxidation and reduction of the graphite felts. Even though this field has been extensively studied by using different techniques, there is still some controversy. It is commonly accepted that chemical/electrochemical oxidation of graphite felts increases their activity towards V(IV)/V(V) reactions (3, 4). However, there are few studies reporting the opposite result (5, 6). It is therefore necessary to perform a fundamental study of the kinetics of vanadium species redox reactions on activated and non-activated graphite felts. The felt material (non-activated or activated) was ground using a mortar and mixed with epoxy resin to form a paste (33wt% of epoxy). The paste was pressed (8000 kg/cm2) in a stainless steel mold until it hardened, and the resultant electrode was employed as the disk in the rotating disk electrode experiments (RDE). To our best knowledge, this is the first RDE study of vanadium reactions on non-activated and activated graphite felts. The results and trends obtained in the RDE studies were verified by performing vanadium flow battery experiments. The presentation will discuss how the RDE disk was made, present the kinetic data of non-activated graphite felt and thermally activated (7) graphite felt for both V(IV)/V(V) and V(II)/V(III) redox reactions. The kinetic analysis will be accompanied with the analysis of the carbon felts by scanning electron microscopy, X-ray photoelectron spectroscopy, and charge/discharge curves in an all-vanadium redox flow battery.