New Diagnostic Technique to Characterize Electro-Kinetics in Redox Flow Battery

As the fraction of electricity generated from intermittent renewable sources (such as solar and wind) grows, developing reliable energy storage technologies to store electrical energy in large scale is of increasing importance. Redox flow batteries (RFB) are regarded as a leading technology in providing a well-balanced solution for current daunting challenges of grid-scale energy storage. Cell-level resistive losses reduce RFB power density and originates from ohmic, kinetic, or mass transfer limitations. existing studies on electron and mass transfer rates are mostly performed in ex-situ conditions based on planar electrodes, so the obtained key parameters are difficult to make specific interference about the performance of a practical electrode in a battery. To address this limitation, an in-situ electroanalytical technique for RFB is proposed for the first time by a symmetrical cell design. For both cathodic and anodic reactions, the polarization curves at condition of a serious of flow rate are obtained on the symmetrical flow cell. The high frequency resistance is also obtained by electrochemical impedance spectroscopy (EIS) at open circuit condition. The ohmic, kinetic and mass transfer resistance can be decomposed from total polarization. Then, the corresponding key parameters, i.e., membrane conductivity, reaction rates, transfer coefficients and mass transfer rates, can be obtained by using a theoretical calculation of specific surface area. The extracted key parameters are validated on both vanadium redox flow battery and aqueous organic redox flow battery.