Using voltammetry augmented with physics-based modeling and Bayesian hypothesis testing to identify analytes in electrolyte solutions

Microelectrode-Based Sensor for Measuring Operando Active Species Concentrations in Redox Flow Cells

“…Most methods for monitoring SOC only measure the ratio of species concentrations in different oxidation states; however, the magnitudes of these concentrations are necessary to determine the SOH and elucidate sources of performance loss (e.g., crossover, species decay, self-discharge). While concentration measurements are often more challenging, electroanalytical techniques are well suited to quantify electroactive species in redox systems. − For example, amperometric measurements have been performed on gas diffusion electrodes to measure vanadium­(IV) and vanadium­(V) concentrations; but despite the robust methodology, the protocol requires specialized equipment to prepare electrodes . Microelectrode voltammetry has also been demonstrated as a viable method for characterizing electrochemical properties, , measuring redox species concentrations, and assessing the decay of active materials ex situ in deterministically prepared electrolytes .…”

Extending and Automating Quantitative Microelectrode Voltammetry through an Oblate Spheroidal Coordinate Framework

“…9,12 Accordingly, significant effort has been devoted to modeling voltammetric systems, and voltammograms in dilute electrolytes may be numerically, semianalytically, and analytically simulated in an array of programming languages (e.g., C++, MATLAB ® ) as well as in commercial or open-source software packages (e.g., COMSOL ® , EC-Lab ® ). 11,[13][14][15][16][17][18][19] Broadly, voltammetric methods polarize the working electrode to observe reactant fluxes that manifest as current, providing mechanistic insight into redox processes of interest. [20][21][22][23][24] A key differentiating factor in this electrochemical response is the radius of the working electrodemacroelectrodes describe radii that are ca.…”

“…9,12 Although such approaches have considerable utility, there are circumstances where steady-state currents do not provide enough information to sufficiently evaluate voltammograms. For example, signal convolution from multiple redox-active species 19 may frustrate such analyses, along with voltammograms that do not have fully developed plateau currents-specifically, voltammograms whose cutoff or turnaround potentials are close enough to the formal redox potential that no clear plateau is observed (e.g., to avoid electrode or electrolyte solution degradation at extreme potentials). 1,25 More generally, by only considering plateau currents, the remainder of the voltammogram, which offers insights into reaction kinetics and thermodynamics, is ignored.…”

“…While steady-state and transient voltammetry models can solve the forward problem-that is, simulating a voltammogram given a set of parameters-they may also be used to solve the inverse problem (e.g., estimating a parameter set given a voltammogram), which, in turn, can be used to estimate the identities and concentrations of analytes in an electrolyte solution via automated algorithms. 19 Closed-form expressions are readily adoptable for this purpose, as they can be computed nearly instantaneously and can be derived with relative ease using the oblate spheroidal coordinate framework. Though models that simulate transience are more difficult to employ for solving the inverse problem (i.e., longer simulation times), oblate spheroidal coordinates still overcome the singularity at the electrode perimeter and thus remain an attractive option for numerical methods.…”

Leveraging graphical models to enhance in situ analyte identification via multiple voltammetric techniques

“…Voltammetry is a foundational electroanalytical technique that has been leveraged for more than a century to evaluate electrochemical reactions, ranging from estimating fundamental transport and kinetic rate constants of analytes within well-defined electrolyte solutions to characterizing constituent components within electrolyte solutions of unknown, and sometimes evolving, composition in electrochemical devices. [1][2][3][4][5][6][7][8][9][10] Often, physical models-either closed-form or otherwise (e.g., finite difference formulations)-accompany voltammetric experiments to facilitate quantitative interpretation of data collected. 1,[10][11][12][13][14][15][16] This union of experiment and simulation provides insights into the physical processes that underpin the current response to changes in the electrode potential, leading to the codification of canonical relationships (e.g., Randles-Ševčik equation, Nicholson relation) 17,18 for a variety of potential waveforms, including cyclic linear sweep voltammetry (i.e., "cyclic voltammetry" (CV)), square wave and cyclic square wave (CSW) voltammetry, and alternating-current voltammetry.…”