Diminished electron transfer kinetics for [Ru(NH3)6]3+/2+, [α-SiW12O40]4-/5-, and [α-SiW12O40]5-/6- processes at boron-doped diamond electrodes

Heterogeneous electron transfer rate constants (k0 values) at a boron-doped diamond (BDD) electrode (10-2 cm s-1 range) that are more than an order of magnitude smaller than found at metal or glassy carbon (GC) electrodes (≥2.0 cm s-1) are reported for the outer-sphere [Ru(NH3)6]3+/2+, [α-SiW12O40]4-/5-, and [α-SiW12O40]5-/6- redox couples in aqueous electrolyte media. The k0 values and other parameters relevant to electrode kinetics were derived from analysis of the higher-order harmonic components available in Fourier transformed large amplitude alternating current voltammetry at BDD, GC, and platinum (Pt) or gold (Au) electrodes for the reduction of highly positively charged [Ru(NH3)6]3+ and highly negatively charged Keggin-type silicon tungstate ([α-SiW12O40]4- and [α-SiW12O40]5-). The slower electron transfer kinetics at the BDD electrode, relative to the other electrode materials, are discussed in terms of the double layer, density of states, and other factors. (Chemical Equation Presented).