Investigation On Electrode Reaction Mechanism for Vanadium Redox Flow Battery

Investigation on Electrode Reaction Mechanism for Vanadium Redox Flow Battery

XIE Xiaofeng¹, YANG Chun¹, WANG Jinhai¹, Shang Yuming¹, WANG Shubo¹, MAO Zongqiang¹ MATHUR V. K²

1. Institute ofNuclear andNew EnergyTechnology, Tsinghua University, Beijing100084, China

2.Department of Chemical Engineering, University of New Hampshire, NH 03824, USA

Abstract:

Vanadium redox flow battery (VRB) employs vanadium ions of different valences as liquid electrolytes. It is independent of storage capacity, output power, normal atmospheric temperature operation, fast response, and long operating life. The VRB system can be widely used for load leveling, distributing power, standby power supply and municipal transport.

In this work, electrochemical impedance spectrum (EIS) technique was employed to investigate the electrode reaction mechanism in anodic electrolyte containing glycerin as an additive for VRB. The spectrums were simulated and analyzed through the equivalent circuit of R_S(C_d(R_pW)). The simulation results showed that with the increase in glycerin content, the solution resistance (R_S), the double electric layer capacitor (C_d) and the polarization resistance (R_p) reduced to the minimum. However, the concentration polarization reached to its maximum when glycerin added was about 1%. It indicated that the glycerin, containing electron-donor group, had effectively promoted the vanadium ion dispersion in solution, so that the solution resistance decreased. When the vanadium ions were combined with glycerin, the increase in molecular volume resulted in the increase in distance of double electric layer, which lead to the decrease of the value of double electric layer capacitor. Because of the increase in electrode reaction, relative concentration difference both in the vanadium ions in solution and on the electrode surface became wider. The adsorption of vanadium ions on the electrode surface was enhanced by added glycerin in anodic electrolyte so as to increase redox catalyst efficiency of anodic electrolyte.

Key words:Vanadium Redox Flow BatteryGGlycerinGElectrolyteGElectrochemical Impedance Spectrum

Acknowledgements

The work was funded by Tsinghua University Initiative Scientific Research Program (201010800623),State Key Laboratory for Automotive Safety and Energy(KF10132), State Key Lab of Power Systems(SKLD10KZ03).