Probing Electrolyte Cation Effects on the Electron Transfer Kinetics of the [α-SiW12O40]4−/5− and [α-SiW12O40]5−/6− Processes using a Boron-Doped Diamond Electrode

• Fourier transformed large amplitude ac voltammetry (FTACV) is a kinetically sensitive technique.
• FTACV was used to probe the cation effect on the kinetics (k0) of [α-SiW12O40]4−/5− and [α-SiW12O40]5−/6− processes.
• k0 can be reliably determined at a boron doped diamond electrode.
• k0 is electrolyte cation dependent, increasing in the order of Li+ < Na+ < K+ ≈ NH4+.
• Diffusion coefficients of [α-SiW12O40]4− vary in different electrolyte media, increasing in the order of LiNO3 < NaNO3 < KNO3 ≈ NH4NO3.

ABSTRACTFourier transformed large amplitude alternating current (FTAC) voltammetry has been used to investigate the electrolyte cation dependence in aqueous media on the electron transfer kinetics (k0 values) of the [α-SiW12O40]4−/5− and [α-SiW12O40]5−/6− one-electron reduction processes of the highly negatively charged Keggin type silicon tungstate [α-SiW12O40]4− at a boron-doped diamond (BDD) electrode. In the presence of alkali metal nitrate electrolytes, k0 values for both processes were reliably determined by FTAC voltammetry at a BDD electrode. This proved possible because much smaller rate constants were found relative to those at the more commonly used glassy carbon electrode where the processes are reversible. Similar k0 values were found for both reduction processes at the BDD electrode and lie in the range of 0.045–0.10 cm s−1, but show a clear electrolyte cation dependence, increasing in the order of LiNO3 < NaNO3 < KNO3 ≈ NH4NO3.

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