A Spotter’s guide to dispersion in non-catalytic surface-confined voltammetry experiments

A Multiple-Technique Approach to Inferring Bio-electrochemical Reaction Parameters

“…22 The magnitude of this noise, as indicated elsewhere, 15 is proportional to the total current. Furthermore, as has been demonstrated previously, 15,19 several of the parameters in table 1 have similar effects over the potential window of interest. This manifests itself as correlations between sets of parameters, as illustrated, for example, for R u and k 0 in figures S1 and S2.…”

“…This is known as parameter compensation. 19 The effect is further compounded by the impact of the background non-Faradaic current on the parameter recovery process, which is described in more detail in the Results section. Overall, this means that the inverse problem is made very difficult by the presence of multiple local minima, often in disparate parts of the overall parameter space.…”

“…It was also determined that the effects of thermodynamic dispersion in the model should be included, from inspection of the r-FTACV experimental harmonics, as described in previous work. 19 This can be achieved by comparing the r-FTACV harmonics against a non-dispersed simulation. Such a simulation can be obtained by fitting to PSV data, and then using the best-fit parameters to obtain an r-FTACV simulation -if the higher r-FTACV experimental harmonics are of a lower magnitude and are wider than the non-dispersed simulation, then Figure 2: A: PSV total current, and two simulations with highly differing parameter values obtained by fitting to PSV total current (referred to as θ 1 and θ 2 , the parameter values of which can be found in the SI in table S1).…”

“…this is an indication that thermodynamic dispersion is present. The presence of thermodynamic dispersion also implies the presence of kinetic dispersion, but in the close-to-reversible kinetic regime, kinetic dispersion does not have a significant effect on the Faradaic current, and so it was not modelled for reasons of computational efficiency 19 After an initial parameter inference attempt, fitting to harmonics 4-10 of the Cj X183 current, it was determined that it was possible to obtain parameter vectors that provided a reasonably good fit to these PSV harmonics, but when compared to r-FTACV harmonics data as shown in figure 3, the fit is poorwith a mismatch between the predicted and experimental harmonic magnitudes, and implausible waveshapes -the parameters used to generate the simulation can be found in table S2 in the SI under "low k 0 ". The poor fit is particularly apparent in r-FTACV harmonic 4, where one single merged set of peaks is visible in the simulation while two separately resolved sets of peaks are observed in the experimental data.…”

A Voltammetric Perspective of Multi-Electron and Proton Transfer in Protein Redox Chemistry: Insights From Computational Analysis of Escherichia coli HypD Fourier Transformed Alternating Current Voltammetry

“…By definition, kinetic dispersion is not possible for a fully reversible electron transfer process that is fully described by the Nernst thermodynamic relationship. Furthermore, the experimental data shows none of the hallmarks of significant thermodynamic dispersiona broadening of the harmonics, and substantial reduction in current amplitude of the higher harmonics relative to the non-dispersed case (Lloyd-Laney et al, 2021a). Since the harmonic simulations generated without dispersion in Figures 2, 3, and Supplementary Figure S8 provide such an excellent fit to the experimental harmonics, it is concluded that the contribution of thermodynamic dispersion is negligible.…”