Surface electron transfer enhanced by molecular oxygen: Droplet and bulk mode experiments on boron-doped diamond electrodes

Abstract

The three-electrode screen printed boron-doped diamond (SP/BDD) sensor fabricated by chemical vapor deposition (CVD) on an alumina substrate allowed testing its different electroanalytical performance in terms of: (1) the termination of the SP/BDDE surface (H- or O-termination), (2) the immersion mode of the SP/BDDE in the analyte solution (B - bulk mode) and in the drop experiment (D - drop mode), and (3) the presence and absence of atmospheric oxygen. The electrochemical methods (CV – cyclic voltammetry, EVLS – elimination voltammetry with linear scan, EIS – electrochemical impedance spectroscopy) were complemented by methods that characterize the surface properties of the electrode material (Raman spectroscopy, SEM – scanning electron microscopy, XPS – X-ray photoelectron spectroscopy, OCA – optical contact angle). Mott-Schottky analysis demonstrated a higher density of free charge carriers and a closer localization of the valence band (VB) to Fermi level for H-termination than for O-termination of surfaces, therefore further experiments were performed on the H-terminated SP/BDDE. The B and D mode tests in the absence and presence of atmospheric oxygen using the redox probe [Fe(CN)6]3−/4- demonstrated a significant difference in both the heterogeneous charge transfer rate constants and charge transfer resistance values. The H-terminated SP/BDDE surface and the D-mode experiment in the presence of O2 provided the best electroanalytical performance of this screen-printed diamond electrode. The O2-enhanced surface electron transfer was discussed in the context of the electrochemical potential model of boron-doped diamond and the used electrolyte.