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Diamond


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Boron doped diamond (BDD) is the subject of considerable interest as an electrode material as a consequence of its very wide potential window in aqueous solution, low background currents, and corrosion stability in aggressive media. In collaboration with the Diamond Physics group at Warwick and Element Six we investigate the link between the material and electrochemical properties with a focus on applications in electroanalysis. Recent highlights include the development of high quality electroanalysis grade all diamond electrodes of any geometry for a wide range of applications (see image left showing BDD electrodes (black) insulated in insulating diamond (transparent)).

For anyone wanting to learn more about working with BDD read: "A Practical Guide to Using Boron Doped Diamond in Electrochemical Research" PCCP, 2015, 17, 2935 click here (PDF Document)


 

For easy use of polycrystalline boron doped diamond (pBDD) in a recognisable electrode format we construct, robust and reliable pBDD macrodisk electrodes [1]. Laser micromachiners are used to cut precise diameter columns from pBDD wafers grown by Element Six to provide optimal electrochemical performance. A reliable ohmic connection is made using an annealed Ti/Au contact. The pBDD is then sealed in a glass capillary so that only the top (disk) surface is exposed and is ready for use.

To verify electrochemical performance, cyclic voltammograms are recorded for the electrolysis of simple outer sphere redox mediators e.g. as shown left, for the reduction of Ru(NH3)63+ at concentrations of 1 and 10 mM (in 0.1 M KCl) at different scan rates. It is important that metal-like characteristics are observed in these simple tests, in order for the BDD to be used in further studies.

References

To understand the performance of polycrystalline BDD electrodes it is important to be able to map the spatial variation in electron transfer kinetics across the surface. This requires the use of electrochemical imaging techniques. The technology has now advanced that it is now possible to obtain micron and sub-micron resolution electrochemical imaging whilst at the same time accurately mapping the topography of the sample, using techniques developed in the group such as intermittent contact-SECM (IC-SECM) and scanning electrochemical cell microscoopy (SECCM).

Using IC-SECM in combination with Raman mapping and localised capacitance measurements it is possible to show that the electron transfer kinetics, correlates exactly with boron dopant levels in the polycrystalline material and local density of states [1].

With SECCM, as solution is only confined to the micron sized imaging capillary and does not bathe the entire sample, diffusion overlap between neighbouring active sites is significantly reduced leading to enhanced electrochemical resolution, as shown [2].

Both techniques show in conjuction with Raman, that the pBDD used (grown by Element Six Ltd.) is of high enough quality that there is NO evidence of inter-facet enhanced electrochemical activity resulting from sp2 inclusion at grain boundaries.

References

1. Hollie V. Patten, Katherine E. Meadows, Laura A. Hutton, James G. Iacobini, Dario Battistel, Kim McKelvey, Alexander W. Colburn, Mark E. Newton, Julie V. Macpherson*, Patrick R. Unwin*, Angew. Chem. Intl. Ed., 2012, 51(28), 7002-7006

2. Hollie V. Patten, Stanley C. S. Lai, Julie V. Macpherson, and Patrick R. Unwin, Anal. Chem., 2012, 84(12), 5427-5432

The unique properties of diamond, including the wide solvent window and low capacitive currents, combined with the quality of diamond available (sp2 free, freestanding BDD wafers), has resulted in the exploration of the real-world applications of BDD here at WEIG. The realisation of the potential of BDD has led to numerous industrial collaborations being established.


The bare surface or functionalised substrate is used for a variety of different sensor applications. For example, using either direct or indirect electrodeposition strategies s it is possible to deposit Pt (direct) [1] and nickel hydroxide (indirect) nanoparticles on the BDD surface of controlled size. These electrodes have been used for the amperometric sensing of oxygen (Pt) and glucose (Ni).


The potential of using Boron Doped Diamond Metal Nanoparticle Functionalised Electrodes for the detection of genotoxic impurities (GIs) such as hydrazine in the pharmaceutical industry has been investigated with support from AstraZeneca, showing that electrochemistry provides a cheaper, simpler alternative to other analytical techniques currently available [2]. Work has also shown that this is amenable for on-line GI detection, showing great industrial viability.


Considered as a way to optimise heavy metal detection, in-situ control of local pH using a pBDD ring disk electrode has been studied, using a novel dual electrode system. Decreasing the local pH by over 4 orders of magnitude has been illustrated, with the pH remaining stable for prolonged periods of time [3].

The development of a novel heavy metal detection analytical technique, Electrochemcal X-ray Fluorescence (EC-XRF) is also underway vastly improving the detection limits compared to traditional EDXRF, by simply coupling a simple electrochemical preconcentration step with EDXRF analysis. Diamond provides the perfect electrode material for this application (low z-number and the wide solvent window). Research into in-situ EC-XRF is now being investigated, which has vast implications for 'in the field' and 'on-line' heavy metal detection [4].


References

1. D. Wakerley, A. G. Güell, L. A. Hutton, T. S. Miller, A. J. Bard, and J. V. Macpherson, Chem. Comm., 2013 49, 5657–5659.

2. R. B. Channon, J. C. Newland, A. W. T. Bristow, A. D. Ray, and J. V. Macpherson, Electroanalysis, 2013, 25 (12), 2613–2619.

3. T. L. Read, E. Bitziou, M. B. Joseph and J.V.Macpherson, Anal. Chem., 2014, 86 (1), 367–371.

4. L. A. Hutton, G. D. O'Neil, T. L. Read, Z. J. Ayres, M. E. Newton and J. V. Macpherson, Anal. Chem, 2014, Accepted.