Solid-state electrochemical behavior of Keggin-type borotungstic acid single crystal

Abstract

We demonstrate the electrochemical characteristics of the, poorly described in the literature, mixed-valence proton conducting solid borotungstic acid single crystal, H 5 BW 12 O 40 xH 2 O, in the absence of liquid electrolyte phase. We performed electrochemical measurements in an all-solid cell with a gold fiber ultramicrodisk (diameter 10, 25, and 40 μm) working electrode, a silver semi-reference disk electrode, and a glassy carbon ring counter electrode. Diagnostic experiments at different scan rates aimed at probing the model of mass transport and potential kinetic limitations. Such bulk parameters as the effective diffusion coefficient of charge propagation and the concentration of mixed-valence redox centers were determined by two methods. The first method is based on the analysis of both Cottrellian and steady-state currents (the mixed-regimes method), and the second method provides the true diffusion coefficient (transport coefficient free of the migration influence) for both the substrate and the product of the electrode reaction. Together, these methods constitute a double potential step chronoamperometry experiment. The data obtained with these electrochemical experiments (effective diffusion coefficients, concentration of mixed-valence redox centers, etc.) can support the results obtained with other techniques (XRD, FTIR, and TGA).

Interfacing a heteropolytungstate complex and gelatin through a coacervation process: design of bionanocomposite films as novel electrocatalysts

“…This increase of the current baseline may be explained by a modication of the interface GCE/electrolyte by the ionic liquid. 32,43 While the E 1 and E 2 peaks have mean potential values (À0.42 and À0.67 V vs. Ag/AgCl respectively) similar to that of [BW 12 O 40 ] 5À in solution (see Fig. 2(a)), the peak E 3 at a mean potential of À0.89 V is shied to a negative value which is consistent with the strong dependence of this peak with pH (vide supra).…”

“…7 In the present work, the coacervation process with gelatin has been extended to a Keggin-heteropolytungstate [BW 12 O 40 ] 5À whose electrochemical characterization of a single crystal has been recently reported. 32 This study shows that crystals of [BW 12 O 40 ] 5À are characterized by a large population of redox sites and mobile protons, and a high effective diffusion coefficient for mass transfer, both requirements for the development of solid state electrochemical devices.…”

Electrochemical and UV–visible spectroscopy studies of K6As2W18−xMoxO62 (x = 0–3) Wells–Dawson heteropolyacid catalysts for oxidative dehydrogenation of benzyl alcohol

“…2 shows the dependence of peak current on square root of scan rate (plotted for peak current of first electron reduction). For all K 6 As 2 W 18 − x Mo x O 62 (x = 0-3), the linear relationship between peak current and square root of scan rate was observed, suggesting that these redox transitions were diffusion-controlled processes expressed by the Randles-Sevcik equation [15]. K 6 As 2 W 18 O 62 exhibited four tungsten-centered redox transitions in this scan range.…”