The activity of non-metallic boron-doped diamond electrodes with sub-micron scale heterogeneity and the role of the morphology of sp2 impurities

The electrochemical activity of low boron-doped diamond electrodes prepared by hot filament chemical vapour deposition with varying methane levels in a hydrogen source gas ratio is studied by cyclic voltammetry (CV), Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical response of the electrodes is found to be inconsistent with the electrodes acting as semi-conducting interfaces i.e. no diode like behaviour is observable. Hence, on the basis of the presence of sp(2) and other non-diamond carbon impurities present in the electrode, the electrochemical response is ascribed as being dominated by these low level impurities masking any response of the boron that may or may not be present. Importantly, near fully reversible voltammetry of the redox probe ruthenium (III) hex amine is recorded and with increasing CH4/H-2 ratio used for the preparation, the CV showed the electro-reduction in aqueous solution is found to exhibit a significant decrease in the voltammetric peak-to-peak separation. This changed electrode response is attributed to the altered morphology and dimensions of the non-diamond and graphitic sp(2) impurities where the larger impurity domains serve to decrease the electrode resistivity. (C) 2016 Elsevier Ltd. All rights reserved.