Electrochemical Impedance Spectroscopic Investigation of Vanadium Redox Flow Battery

Abstract

The kinetics of redox reactions relevant to vanadium redox flow battery (VRFB) were investigated using voltammetry and electrochemical impedance spectroscopy in a three-electrode configuration and in a VRFB setup (two-electrode configuration). Impedance spectra were recorded in the VRFB configuration with equimolar concentrations of V5+/V4+ and V3+/V2+ solutions as positive and negative electrolytes, respectively (full-cell; asymmetric feed system); with an equimolar V5+/V4+ electrolyte on both sides (symmetric feed system 1), and also with V3+/V2+ electrolyte on both sides (symmetric feed system 2). Impedance of the full-cell VRFB (recorded with asymmetric feed system) is comparable to the sum of the half of the impedance of symmetric feed systems (of V5+/V4+ and V3+/V2+ electrolytes) at open circuit potential . Impedance and voltammograms recorded in the three-electrode configuration using Vulcan XC-72 modified rotating disk electrode, and impedance recorded in the two-electrode full-cell configuration unequivocally confirm that the V5+/V4+ redox reaction limits the VRFB performance. The optimal performance of the VRFB with the in-situ treated carbon felt compressed to 47 % is ~389 and ~336 mW cm-2 with 5 and 25 cm2 cell area, respectively.

A Stable and Energy-Dense Polysulfide/Permanganate Flow Battery

“…Before the long-term cycling tests, S/Mn RFB cells with variable concentrations (0.1 1.0, 2.0, 3.0, and 3.92 M) of NaMnO 4 in 5.0 M NaOH as the catholyte while 2.0 M Na 2 S 2 in 5.0 M NaOH as the anolyte were assembled and analyzed by EIS results (Figure S10). Two semicircles are well-resolved which denote the mass-transfer resistance (R 2 ) in the low-frequency region and the charge-transfer resistance (R 3 ) in the high-frequency region . Besides, when NaMnO 4 becomes concentrated, both R 2 and R 3 decrease owing to the increased number of ions in the catholyte.…”

“…Two semicircles are well-resolved which denote the mass-transfer resistance (R 2 ) in the low-frequency region and the chargetransfer resistance (R 3 ) in the high-frequency region. 54 Besides, when NaMnO 4 becomes concentrated, both R 2 and R 3 decrease owing to the increased number of ions in the catholyte. Furthermore, with 3.92 M NaMnO 4 in the catholyte, the S/Mn cell stably runs over 50 cycles with high efficiency (Figure 5a).…”

The impact of overpotential on the enthalpy of activation and pre-exponential factor of electrochemical redox reactions

“…A starting solution of 1.0 M VOSO 4 (VO 2+ ) in 3 M H 2 SO 4 was used to prepare the VO 2 + by the electrolysis of VO 2+ using a vanadium redox flow battery test station (Fuel Cell Technologies). 47 The VRFB of 25 cm 2 cell area was constructed with carbon felts as both positive and negative electrodes separated by a Nafion™ 117 membrane. Both the electrolytic tanks were filled with VO 2+ solution and a constant voltage of 1.7 V was applied to the cell with an electrolyte flow rate of 20 mL min −1 .…”

Implications of Polyoxometalate Properties on the Performance Characteristics of Redox Flow Battery

“…However, these RFBs have sluggish reaction kinetics and require highly concentrated electrolytes for the desired performance. [7][8][9][10][11][12][13] Other redox flow batteries reported in the literature include inorganic metal ion-based redox couples, such as Cr-Fe, [14][15][16][17] and hybrid flow batteries such as Pb-acid [18][19][20] and Zn-Br 2 . 21 The high rate of self-discharge, dendrite formation, cross-over, and limited cycle life are some of the problems associated with the metal containing redox species.…”