Boron-doped Diamond Electrodes: Electrochemical, Atomic Force Microscopy and Raman Study towards Corrosion-modifications at Nanoscale

Abstract

Comparative studies of boron-doped diamonds electrodes (polycrystalline, single-crystalline, H-/O-terminated, and with different sp3/sp2 ratios) indicate morphological modifications of diamond which are initiated by corrosion at nanoscale. In-situ electrochemical AFM imaging evidences that the textural changes start at non-diamond carbonaceous impurity sites treated at high positive potentials (>2.2 V vs. Ag/AgCl). The primary perturbations subsequently develop into sub-micron-sized craters. Raman spectroscopy shows that the primary erosion site is graphite-like (sp2-carbon), which is preferentially removed by anodic oxidation. Other non-diamond impurity, viz. tetrahedral amorphous carbon (t-aC), is less sensitive to oxidative decomposition. The diamond-related Raman features, including the B-doping-assigned modes, are intact during reversible electrochemical charging/discharging, which is a salient difference from all usual sp2-carbons. The electrochemical oxidation partly transforms a hydrogen-terminated diamond surface to O-terminated one, but the electrocatalytic activity of plasmatically O-terminated diamond is not achieved for a model redox couple, Fe3+/2+. Electrochemical impedance spectra were fitted to six different equivalent circuits. The determination of acceptor concentrations is feasible even for highly-doped diamond electrodes.