In-Situ Measurement of Vanadium Crossover for the Vanadium Redox Flow Battery

Abstract

A simple in-situ method for the quantification of the crossover in redox flow batteries, adapted from an electrochemical method currently used for quantifying the hydrogen crossover in fuel cells, is proposed and used for characterizing a vanadium redox flow battery. A linear sweep voltammetry (LSV) scan is performed with the pertinent redox species in one side of the electrochemical cell, while in the other side is the supporting electrolyte. The LSV plot should display a plateau where the current is limited by the crossover of the selected species. The crossover results were compared with an external analytical method using MP-AES, showing very good agreement with a maximum relative difference of 6%. This method was used to quantify the crossover of all vanadium species using both cation and anion exchange membranes. The proposed method can be applied for assisting the development and characterization of ion-exchange membranes for redox flow batteries and for in-situ diagnosis of component degradation and failure in RFB systems without disassembling them.

Montmorillonite-Based Separator Enables a Long-Life Alkaline Zinc–Iron Flow Battery

“…The zeta potential of Na-MMT is about −29 mV (Figure 2), indicating that the charge on the surface of Na-MMT is negative. Thus, although the channel of Na-MMT is larger than the size of the hydrated diameter of the Fe(CN) 6 3− ion, 42 it is difficult for the active materials of the anolyte (Zn(OH) 4 2− ) and catholyte (Fe(CN) 6 4− /Fe(CN) 6 3− ) to permeate through the channel of Na-MMT because of its negatively charged property. This negatively charged montmorillonite can also adjust the distribution of Zn(OH) 4 2− ions at the interface between the negative electrode and the membrane through the charge repulsion effect, which is expected to regulate the deposition direction and morphology of metallic zinc during charging of the battery.…”

“…After desolvation, the active material adsorbs on the electrode and receives two electrons to form metallic zinc. In this process, the electrochemical reaction rate of active material on the electrode is much faster than the diffusion rate of active material from bulk solution to the electrode's surface, which can easily lead to concentration polarization on the electrode and further enable the plating of Zn(OH) 4 2− in a direction opposite its diffusion path. This in turn results in a heterogeneous plating of the zincate ion on the electrode and makes the formation of dendritic zinc easy on the electrode.…”

“…Among the electrochemical energy storage technologies, flow batteries have demonstrated very promising prospect in the field of energy storage because of their advantages of high safety, flexibility, and long cycle life. , As a typical representative of flow battery technology, vanadium flow batteries (VFBs) have the unique advantage of using redox pairs based on the same chemical element in both the catholyte and anolyte. , However, the relatively high cost of battery materials (electrolytes and Nafion membrane) and the low energy density of VFB remain big challenges to its industrial implementation. − In the past decade, numerous new types of flow batteries with low cost and high energy density have been developed, such as zinc-based flow batteries, − phenazine-based flow batteries, quinone-based flow batteries, and tetramethylpiperidine 1-oxyl radical (TEMPO)-based flow batteries, which have shown promise for energy storage applications.…”

“…15−17 Similar to the plating−stripping process of lithiumbased batteries, 18,19 the redox reaction in the anode for AZIFB experiences a plating−stripping process during charging− discharging of the battery. During the charging process, the active material (Zn(OH) 4…”

A method for quantifying crossover in redox flow cells through compositionally unbalanced symmetric cell cycling

“…9,19 To isolate membrane / separator contributions, earlier efforts have established methods for monitoring crossover under controlled conditions with applied electric fields. [20][21][22][23][24][25][26] For example, Sing and Meyers previously demonstrated a 4-chamber, 3-membrane redox flow cell design, 20 enabling direct quantification of individual modes of active species transport and leading to adoption by others in the RFB community. 21,22 However, these experiments require a customized cell architecture and continuous electrolyte monitoring, challenging broad implementation and highthroughput experimentation.…”