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 ( k 0 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(NH 3 ) 6 ] 3+/2+, [α-SiW 12 O 40 ] 4–/5–, and [α-SiW 12 O 40 ] 5–/6– redox couples in aqueous electrolyte media. The k 0 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(NH 3 ) 6 ] 3+ and highly negatively charged Keggin-type silicon tungstate ([α-SiW 12 O 40 ] 4– and [α-SiW 12 O 40 ] 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.