Acta Phys. -Chim. Sin. ›› 2006, Vol. 22 ›› Issue (04): 403-408.doi: 10.1016/S1872-1508(06)60012-0

• ARTICLE • Previous Articles     Next Articles

Investigations on the Electrode Process of Concentrated V(IV)/V(V) Species in a Vanadium Redox Flow Battery

WEN Yue-Hua;ZHANG Hua-Min;QIAN Peng;ZHAO Ping;ZHOU Han-Tao;YI Bao-Lian   

  1. Full Cell R&D Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China; Chemical Defence Institute, Beijing 100083, P. R. China
  • Received:2005-09-08 Revised:2005-11-14 Published:2006-04-10
  • Contact: ZHANG, Hua-Min

Abstract: The electrode process of concentrated V(IV)/V(V) species has been studied at a graphite electrode using cyclic voltammetry, linear polarization, and impedance techniques. The results have revealed that in H2SO4 solution below 2 mol•L-1 containing 2.0 mol•L-1 V(IV), the electrode process of V(IV)/V(V) is controlled by the electrochemical polarization and diffusion with poor reversibility. When the concentration of H2SO4 is above 2 mol•L-1, the electrode process of V(IV)/V(V) turns into the diffusion control with improvement of the reversibility. An increase in concentration of H2SO4 solution facilitates a decrease in impedance, whereas too high concentration of H2SO4 solution(>3 mol•L-1) results in a remarkable increase in the viscosity of solution leading to a large mass transportation polarization, and thus the impedance starts to increase a bit. In 3 mol•L-1 H2SO4 solution, the reversibility and kinetics of V(IV)/V(V) are improved gradually as well as the characteristics of impedance with increasing concentration of V(IV) solution. But, when the concentration of V(IV) solution exceeds 2.0 mol•L-1, the viscosity of the solution is so high that the mass transportation polarization increases considerably, resulting in the deterioration of electrochemical performance of V(IV)/V(V) species and an increase in impedance. Therefore, considering from standpoint of increasing the energy density and electrode kinetics comprehensively, the optimal concentration of H2SO4 is 3 mol•L-1 containing 1.5~2.0 mol•L-1 of V(IV).

Key words: Vanadium redox flow battery, V(IV)/V(V), High concentration, Electrode process