Electrode Material Dependence of the Electron Transfer Kinetics Associated with the [SVW₁₁O₄₀]^3-/4- (V^V/IV) and [SVW₁₁O₄₀]^4-/5- (W^VI/V) Processes in Dimethylformamide

In this study, large amplitude Fourier transformed alternating current (FTAC) voltammetry has been used to determine the heterogeneous electron-transfer kinetics (k° and α values) associated with the vanadium [SVW₁₁O₄₀]^3-/4- (V^V/IV, E° = 0.050 V vs. Fc/Fc⁺, where Fc = ferrocene) and tungsten [SVW₁₁O₄₀]^4-/5- (W^VI/V, E° = -1.530 V vs. Fc/Fc⁺) processes in dimethylformamide containing tetrabutylammonium hexafluorophosphate as the supporting electrolyte. At glassy carbon (GC), platinum (Pt), gold (Au) and boron-doped diamond (BDD), the V^V/IV process is kinetically more facile than the W^VI/V one. Excellent simulation-experiment fits were achieved for the V^V/IV process at all electrode materials, and at a supporting electrolyte concentration of 0.1 M, the k° value associated with this process increases in the order BDD <Pt ≈ Au <GC. By contrast, at all electrode materials except GC, generally poor simulation-experiment fits were achieved for the W^VI/V process, preventing the data from being analysed quantitatively by FTAC voltammetry. Changing the concentration of supporting electrolyte from 0.1 to 0.5 M has a significant influence on the kinetics, with the k° value increasing at GC and decreasing at Pt, Au and BDD. Overall, the findings indicate that differences in density of states do not fully explain the electrode material dependence of the k° values and that other factors such as surface functional groups (on GC) and the double layer effect need to be taken into consideration.