Microelectrode-Based Sensor for Measuring <i>Operando</i> Active Species Concentrations in Redox Flow Cells

The assessment of candidate materials for redox flow batteries requires effective diagnostic techniques monitoring the evolution electrolyte state charge and health to interrogate time-dependent changes in system behavior. Further, such tools can be applied practical embodiments inform maintenance schedules optimize energy utilization. In this work, we develop test a flow-through, microelectrode-based electrochemical sensor continuously measure active species concentrations cells. A gold microelectrode (working electrode) platinum wire (pseudoreference are sealed into stainless steel fitting (counter electrode), three-electrode electroanalytical (i.e., voltammetry, chronoamperometry) performed correlate steady-state current concentration. To validate transport thermodynamics that govern sensing mechanism, combine multiphysics simulation with ex situ experimental testing, confirming device is capable accurately determining individual concentrations. We then evaluate symmetric cell, demonstrating utility approach measuring operando concentrations, discuss additional considerations successful implementation (e.g., measurement protocol, material selection, cell design). Assembled from commercially available, off-the-shelf components, readily adopted by research laboratories integrated existing workflows, making it promising tool studying battery materials.