Enhanced performance of a Bi - modified graphite felt as the positive electrode of a vanadium redox flow battery

Graphite felt modified with nanodispersed bismuth was studied as electrode in the positive half-cell of a vanadium redox flow battery (VRFB). The felt was easily modified by immersion in a Bi2O3 solution followed by thermal reduction at 450°C in air. Despite the low metal content (1 at. %), the Bi-modified felt showed an excellent electrochemical performance (at 1 mVs) in terms of anodic and cathodic peak current densities (21 and 17 mA/cm, respectively), reversibility (ΔEp = 0.050 V) and overpotential for the V(IV)/V(V) redox reactions. Furhtermore, repetitive cyclic voltammetry measurements, at various scan rates, evidenced the long term stability of this material. These results demonstrate that bismuth nanoparticles on the carbon surface act as stable active sites to promote these reactions, and represent a significant step forward towards the development of outstanding electrode materials for VRFB.