Thermodynamics, Electrode Kinetics, and Mechanistic Nuances Associated with the Voltammetric Reduction of Dissolved [n-Bu₄N]₄[PW₁₁O₃₉{Sn(C₆H₄)C≡C(C₆H₄)(N₃C₄H₁₀)}] and a Surface-Confined Diazonium Derivative

Abstract

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A perceived paucity of quantitative studies in the modern era of voltammetry: prospects for parameterisation of complex reactions in Bayesian and machine learning frameworks

“…If a single set of thermodynamic kinetic parameters and planar diffusion are used then detailed reports of statistics describing the level of agreement of experimental data with that predicted by models would be advantageous. An indirect way of addressing this issue would be to define how good a fit of the experimental data actually is achieved, if the impact of heterogeneity or other non-idealities is not accommodated in the modelling [24].…”

Electrode Material Dependence, Ion Pairing, and Progressive Increase in Complexity of the α-[S2W18O62]4–/5–/6–/7–/8–/9–/10–Reduction Processes in Acetonitrile Containing [n-Bu4N][PF6] as the Supporting Electrolyte

“…Because surface accumulation continues to increase at potentials where α-[S 2 W 18 O 62 ] 7– and even higher negatively charged species are generated, departures in experimental versus simulated data comparisons are anticipated to progressively increase for the α-[S 2 W 18 O 62 ] 7–/8– , α-[S 2 W 18 O 62 ] 8–/9– , and α-[S 2 W 18 O 62 ] 9–/10– processes, which occur at more negative potentials and at longer times after the onset of the α-[S 2 W 18 O 62 ] 6–/7– process. A mass increase and electrode blockage were also reported on the basis of EQCM data at a gold electrode in a recent study on the reduction of [ n -Bu 4 N] 4 [PW 11 O 39 {Sn­(C 6 H 4 )­CC­(C 6 H 4 )­(N 3 C 4 H 10 )}] …”

“…The electrolyte concentration and the potential dependent effect are related to the PZC, which in turn is electrode material-dependent . It has been well established that even the oxidized forms of negatively charged POMs can adsorb spontaneously at carbon, Au, and Pt electrodes. − The combination of more negative potentials where [ n -Bu 4 N] + concentrations in the double-layer region are considerably higher than in bulk solution and extensive reduction leading to very high charges on the POMs may even provide scenarios where the solubility product is exceeded at the solution–electrode interface, leading to precipitation of POM or specific adsorption of reduced POM which partially blocks the electrode and alters the mass transport, thereby leading to departure from theoretical predictions based on the Butler–Volmer electrode kinetics and linear diffusion as found in this and other studies . It needs to be remembered that the solubility products of [ n -Bu 4 N] + salts of [S 2 W 18 O 62 ] 8– , [S 2 W 18 O 62 ] 9– , or [S 2 W 18 O 62 ] 10– , for example, have a [ n -Bu 4 N] + concentration term raised to power 8, 9, and 10, respectively.…”

Covalent Attachment of Polyoxometalates to Passivated Si(111) Substrates: A Stable and Electronic Defect-Free Si|POM Platform

“…E 1/2,W2 is in good agreement with the E 1/2 of the (4–/5−) conversion of a similar POM system reported by Proust et al consisting of [PW 11 O 39 {Ge­(p-C 6 H 4 –CC–C 6 H 4 –N 2 + )}] 3– (POM-N 2 + ) covalently attached to hydride-terminated n + -Si­(100) ( Si|POM-N 2 + ), which was reported at −1330 mV vs Fc/Fc + (−0.95 V vs SCE) at low scan rates. , The W1 anodic shoulder and broadening of W2 at high scan rates are attributed to the presence of an equilibrium of diverse POM protonation states. POM protonation is known to contribute to redox potential dispersion of similar POM species exposed to acidic protons. , In this case, the presence of residual H + used to charge-balance the parent (TBA) 4 H 3 [PW 11 O 39 ] POM, carboxylic acid groups of organogermanium linkers from untethered POM Ge -COOH, or other adventitious sources could have each contributed to protonation of POMs during CV experiments. Redox features with similar characteristics as those observed in the CVs of n + -Si|POM Ge samples were also present in CVs of the solvated POM Ge -COOH species at glassy carbon working electrodes in dry MeCN containing 0.1 TBAPF 6 (Figure S4).…”

“…Covalent methods also provide greater control over key monolayer criteria, including the density of immobilized POMs and the distance between POMs and the electrode surface, which each contribute to overall device performance . Recently, notable advances in covalent POM attachment procedures have been achieved using the synthetically versatile lacunary Keggin-type heteropolytungstates − and molybdates. , These mono-vacant clusters readily incorporate organo-silanes, -germanes, and -stannanes that can contain functional groups for subsequent covalent bond-forming reactions . In this manner, Keggin-type POMs have been functionalized with organic linkers containing unsaturated terminal bonds and diazonium functional groups for covalent bonding to hydride-terminated silicon (Si–H) electrodes via hydrosilylation or radical diazonium reduction, respectively. ,,, …”