Influence of boron content on the morphological, spectral, and electroanalytical characteristics of anodically oxidized boron-doped diamond electrodes

The effect of boron content in nanocrystalline anodically polarized boron doped diamond (BDD) thin films deposited at B/C ratio 500 ppm - 8000 ppm on their morphology, quality, and electrochemical and spectral properties was investigated using scanning electron and atomic force microscopies and Raman spectroscopy, where the shift of maximum Lorentzian component of diamond phonon at ∼1332 cm−1 was used as the function of boron concentration. Cyclic voltammetry with the outer- and inner sphere redox markers ([Ru(NH3)6]3+/2+ and [Fe(CN)6]3−/4−) enables to differentiate among the semiconductive films (500 ppm and 1000 ppm) and films with metallic conductivity (2000 ppm - 8000 ppm). Nevertheless, only the inner sphere character of [Fe(CN)6]3−/4− redox marker enables to visualize the differences between individual boron content for metallic films. Further, reversible behavior with ΔEp of 59.8 ± 0.9 mV (n = 5) and Ipa/Ipc ratio 1.00 at the scan rate of 100 mV s−1 was achieved for this redox marker at 2000 ppm film; this film just above the semiconductive/metallic threshold exhibited also favorable spectral (e.g., roughness surface factor) and electrochemical characteristics. The width of the potential window in aqueous media of different pH values and in wide variety of supporting electrolytes decreases with increasing boron content, with independence of anodic potential limit for 2000 ppm - 8000 ppm electrodes and more pronounced dependence of cathodic potential limit on boron content for all tested BDD films. Further, well-defined and highly reproducible anodic DP voltammetric peak of 2-aminobiphenyl with peak current increasing with boron content were obtained at ca +0.7 V (vs. Ag/AgCl/3 mol L−1 KCl) at all BDD films tested.