A microelectrode-based sensor for measuring operando active species concentrations in redox flow cells

Abstract

The assessment of candidate materials for redox flow batteries requires effective diagnostic techniques for monitoring the evolution of electrolyte state of charge and state of health to interrogate time-dependent changes in system behavior. Further, such tools can be applied in practical embodiments to inform maintenance schedules and optimize energy utilization. In this work, we develop and test a flow-through, microelectrode-based electrochemical sensor to

State and Prospects of Unbalanced, Compositionally Symmetric Flow Battery Cycling and Steady-State Amperometry Techniques for Electrolyte Stability Assessment: The Case of Methyl Viologen

“…The SOH at each measurement step was calculated according to eq 10 and as described in the literature. 14,15 For comparison, a new temperature correction approach was applied according to eq 11.…”

“…In contrast to that, ex situ stability assessment techniques overcome these issues by investigating the flow battery electrolyte itself under isolated conditions. So far, in the literature, ex situ stability measurement techniques are mostly represented by spectroscopic 8,13,14 and electrochemical methods. 14−19 Spectroscopy is capable of providing high accuracy; however, it requires special equipment, preliminary calibration, temperature control, or corrections, and it can often struggle with interference of other electrolyte components with the signal of the redox-active substance under investigation.…”

“…14,15,17−19 In particular, Brushett and co-workers proposed that redox species concentrations can be monitored both in situ and ex situ using the mass-transfer-limited current at microelectrodes. 14,15 Consequently, in this contribution, we aim to directly compare the most recent in situ and ex situ approaches for the long-term stability assessment of flow battery electrolytes and, thus, to provide an evaluation of the current status and prospects of the stability assessment methods in this research field. The N,N′-dimethyl-4,4′-bipyridinium dichloride (MV) molecule is chosen as an easily assessable, stable benchmark substance for the capacity fade rate measurement.…”

Towards a mechanically rechargeable solid fuel flow battery based on earth-abundant materials

“…1-10 µm) produces steady-state currents that simultaneously describe the charged and discharged active species concentrations, which, in turn, can be processed to estimate the solution SOC and state-of-health (SOH). [19][20][21] Figure 2a shows representative microelectrode voltammograms acquired on a carbon fiber This analysis enables a general trend to be discerned beyond the specific redox couples examined;…”

Towards a mechanically rechargeable solid fuel flow battery based on earth-abundant materials

“…1-10 µm) produces steady-state currents that simultaneously describe the charged and discharged active species concentrations, which, in turn, can be processed to estimate the solution SOC and state-of-health (SOH). [20][21][22] Figure 2a shows representative microelectrode voltammograms acquired on a carbon fiber working electrode throughout the experiment, depicting changes in the steady-state current plateaus representative of the time-dependent SOC. To increase the rate of Zn / 2-HNQ mixing and potentially the rate and extent of the chemical redox reaction at the upper limits of SOC, sparging was more aggressively conducted starting at 70 min; the stir rate, in turn, was increased from 600 to 1400 rpm at 80 min for the same purpose.…”