Tailoring boron doped diamond surface properties for sensing applications

Abstract

Boron doped diamond (BDD) has found numerous applications for electroanalysis in recent years. It’s material properties set it apart from other electrode materials due to its oft quoted wide solvent window and low background capacitances. However, the electrochemical performance has been shown to be highly dependent on the quality of the material, in particular it’s sp2 carbon content. For some applications, such as pH sensing, it has been shown that the inclusion of sp2 carbon impurities is advantageous. This can be achieved during diamond growth or by post-processing procedures, such as laser micromachining, as has been used in this thesis. Herein methods for electrochemically measuring surface sp2 carbon have been developed, and the functional groups on the electrode surface used for pH sensing applications and the underlying sp2 carbon component for dissolved oxygen sensing via the oxygen reduction reaction. To develop a pH sensor that works in unbuffered solutions laser micromachining, with control of the quinone surface coverage, was combined with pulsed voltammetric techniques to avoid perturbing the interfacial environment and control the local pH change. To further enhance pulsed voltammetric techniques, as used throughout this thesis, the raw current-time data was captured and post processed to extract information on the non-faradaic processes occurring, in addition to optimising the faradaic response. This work together advances the understanding of the effect of sp2 carbon in BDD electrodes and its use for electrochemical applications that requires optimisation of the material properties and electrochemical methods