[show abstract][hide abstract] ABSTRACT: In order to produce polycrystalline oxygen-terminated boron doped diamond (BDD) electrodes suitable for electroanalysis, i.e. widest solvent window, lowest capacitive currents, stable and reproducible current responses and capable of demonstrating fast electron transfer, for outer sphere redox couples, the following factors must be considered. The material must contain enough boron that the electrode shows metal-like conductivity, electrical measurements demonstrate this is achieved at [B] > 1020 B atoms cm-3. Even though BDD contains a lower density of states than a metal it is not necessary to use extreme doping levels to achieve fast heterogeneous electron transfer (HET). An average [B] ~ 3 x 1020 B atoms cm-3 was found to be optimal; increasing [B] results in higher capacitive values and increases the likelihood of non-diamond-carbon (NDC) incorporation. As grown surfaces, i.e. hydrogen-terminated are unsuitable for electroanalysis as the surface is electrochemically unstable, even under very mild electrochemical potentials at pH neutral conditions. Hydrogen-termination can also cause a semi-conducting BDD electrode to behave ~ metal-like due to the additional surface conductivity hydrogen-termination brings. Thus unless [B] of the material is known the electrochemical properties of the electrode may be incorrectly interpreted. It is essential during growth that NDC is minimized as it acts to increase capacitive currents and decrease the solvent window. We found complete removal of NDC after growth using aggressive acid cleans, acid cycling and diamond polishing impossible. Although hydrogen-termination can mask the NDC signature in the solvent window and lower capacitive currents, this is not a practical procedure for improving sensitivity in electroanalysis. For the optimal pBDD electrode alumina polishing was found to be an effective way to produce well-defined, stable and reproducible surfaces, which support fast (reversible) HET for Fe(CN)64- electrolysis. This is the first time this has been reported at an NDC-free oxygen-terminated surface.
[show abstract][hide abstract] ABSTRACT: A Multi-Microscopy Approach has allowed electrochemical reaction rates to be linked to the corresponding dopant levels in polycrystalline boron-doped diamond electrodes. In their Communication on page 7002 ff., P. R. Unwin, J. V. Macpherson, et al. combine high-resolution electrochemical imaging, micro-Raman, and electron-microscopy data to demonstrate that spatially heterogeneous electron-transfer kinetics correlate directly with the local density of electronic states.
Angewandte Chemie International Edition 07/2012; 51(28):7049. · 13.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Conducting carbon materials: a multi-microscopy approach shows that local heterogeneous electron-transfer rates at conducting diamond electrodes correlate with the local density of electronic states. This model of electroactivity is of considerable value for the rational design of conducting diamond electrochemical technologies, and also provides key general insights on electrode structure controls in electrochemical kinetics.
Angewandte Chemie International Edition 06/2012; 51(28):7002-6. · 13.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The development of the first all-diamond hydrodynamic flow device for electroanalytical applications is described. Here alternate layers of intrinsic (insulating), conducting (heavily boron doped), and intrinsic polycrystalline diamond are grown to create a sandwich structure. By laser cutting a hole through the material, it is possible to produce a tubular flow ring electrode of a characteristic length defined by the thickness of the conducting layer (for these studies ∼90 μm). The inside of the tube can be polished to 17 ± 10 nm surface roughness using a diamond impregnanted wire resulting in a coplanar, smooth, all-diamond surface. The steady-state limiting current versus volume flow rate characteristics for the one electron oxidation of FcTMA(+) are in agreement with those expected for laminar flow in a tubular electrode geometry. For dopamine detection, it is shown that the combination of the reduced fouling properties of boron doped diamond, coupled with the flow geometry design where the products of electrolysis are washed away downstream of the electrode, completely eradicates fouling during electrolysis. This paves the way for incorporation of this flow design into online electroanalytical detection systems. Finally, the all diamond tubular flow electrode system described here provides a platform for future developments including the development of ultrathin ring electrodes, multiple apertures for increased current response, and multiple, individually addressable ring electrodes incorporated into the same flow tube.