Nanorod Niobium Oxide as Powerful Catalysts for an All Vanadium Redox Flow Battery

Abstract

A powerful low-cost electrocatalyst, nanorod Nb₂O₅, is synthesized using the hydrothermal method with monoclinic phases and simultaneously deposited on the surface of a graphite felt (GF) electrode in an all vanadium flow battery (VRB). Cyclic voltammetry (CV) study confirmed that Nb₂O₅ has catalytic effects toward redox couples of V­(II)/V­(III) at the negative side and V­(IV)/V­(V) at the positive side to facilitate the electrochemical kinetics of the vanadium redox reactions. Because of poor conductivity of Nb₂O₅, the performance of the Nb₂O₅ loaded electrodes is strongly dependent on the nanosize and uniform distribution of catalysts on GF surfaces. Accordingly, an optimal amount of W-doped Nb₂O₅ nanorods with minimum agglomeration and improved distribution on GF surfaces are established by adding water-soluble compounds containing tungsten (W) into the precursor solutions. The corresponding energy efficiency is enhanced by ∼10.7% at high current density (150 mA·cm^–2) as compared with one without catalysts. Flow battery cyclic performance also demonstrates the excellent stability of the as prepared Nb₂O₅ catalyst enhanced electrode. These results suggest that Nb₂O₅-based nanorods, replacing expensive noble metals, uniformly decorating GFs holds great promise as high-performance electrodes for VRB applications