Name: assessment of boron doped diamond electrode quality and application to in situ modification of local ph by water electrolysis
Uploaded: 2016-01-06T13:00:01
Description: Watch this Scientific Journal Video about Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis at JoVE.com

We would like to thank Dr. Jonathan Newland for the photograph in Figure 4B and for processing optical microscope images for the video, Miss Jennifer Webb for advice and visuals on contact angle measurements, Miss Sze-yin Tan for the solvent window data in Figure 2B, Dr Maxim Joseph for advice on Raman spectroscopy, and also members of the Warwick Electrochemistry and Interfaces Group who have helped to develop the protocols described herein. We would also like to thank Max Joseph, Lingcong Meng, Zoe Ayres and Roy Meyler for their part in filming the protocol.

NOTE: BDD electrodes are most commonly grown using chemical vapor deposition techniques, attached to a growth substrate. They leave the growth chamber H-terminated (hydrophobic). If grown thick enough the BDD can be removed from the substrate and is termed freestanding. The freestanding BDD growth surface is often polished to significantly reduce surface roughness. Cleaning the BDD in acid results in an oxygen (O)-terminated surface.
1. Acid Cleaning BDD
<ol>
	<li>Place a beaker of concentrated sulfuric acid (H<...

Starting with an O-terminated surface is advocated because the H-terminated surface is electrochemically unstable, especially at high anodic potentials7,40,41. Changing surface termination can affect the electron transfer kinetics of inner sphere couples, such as water electrolysis (used herein to change the local solution pH). Furthermore, if the BDD contains significant NDC at grain boundaries it is also possible that upon application of the extreme anodic/cathodic potentials advocated in this article for pH...

Choice of electrode material is of great importance when conducting any electroanalytical study. In recent years, sp3 carbon (diamond) doped with sufficient boron to render the material &#34;metal-like&#34; has become a popular choice for a wide range of electroanalytical applications due to its excellent electrochemical (and thermal and mechanical) properties1,2,3. These include corrosion resistance under extreme solution, temperature and pressure conditions4 ultra-wide solvent windows, low background currents, and reduced fouling, in comparison to other commonly used electrode materials5-7,3. However, increasing non-diamond-carbon (NDC: sp2) content results in a decreasing solvent window, increasing background currents7,8, changes in both structural integrity and sensitivity towards different inner sphere redox species, e.g. oxygen9-12.
Note for some applications, NDC presence is seen as advantageous13. Furthermore, if the material does not contain sufficient boron it will behave as a p-type semi-conductor and show reduced sensitivity to redox species in the reductive potential window, where the material is most depleted of charge carriers7. Finally, the surface chemistry of boron doped diamond (BDD) can also play a role in the observed electrochemical response. This is especially true for inner sphere species which are sensitive to surface chemistry and lower doped diamond where a hydrogen (H-)-terminated surface may make a semi-conducting BDD electrode appear &#34;metal-like&#34;7.
To take advantage of the superior properties of BDD, it is often essential the material is sufficiently doped and contains as little NDC as possible. Dependent on the method adopted to grow the BDD, the properties can vary14,15. This paper first suggests a materials and an electrochemical characterization protocol guide for assessing BDD electrode suitability prior to use (i.e. sufficient boron, minimal NDC) and then describes one application based on locally changing pH electrochemically using the protocol-verified electrode. This process takes advantage of the surface resilience of NDC-free BDD towards corrosion or dissolution under application of extreme applied potentials (or currents) for long periods of time. In particular the use of a BDD electrode to generate stable proton (H+) or hydroxide (OH-) fluxes due to electrolysis (oxidation or reduction respectively) of water in close proximity to a second (sensor)16,17 is described herein.
In this way it is possible to control the pH environment of the sensor in a systematic way, e.g. for pH titration experiments, or to fix the pH at a value where the electrochemical process is most sensitive. The latter is especially useful for applications where the sensor is placed at the source, e.g. river, lake, sea and the pH of the system is not optimal for the electrochemical measurement of interest. Two recent examples include: (i) generation of a localized low pH, in a pH neutral solution, for the electrodeposition and stripping of mercury17; note BDD is a favored material for electrodeposition of metals due to the extended cathodic window9,18,19. (ii) Quantification of the electrochemically detectable form of hydrogen sulfide, present at high pH, by locally increasing the pH from neutral to strongly alkaline16.

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			<td height="20" style="height:20px;width:117px;">Pt Wire</td>
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			<td style="width:117px;">Counter Electrode</td>
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			<td height="100" style="height:100px;width:117px;">Saturated Calomel Electrode</td>
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			<td height="20" style="height:20px;width:117px;">Raman</td>
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assessment of boron doped diamond electrode quality and application to in situ modification of local ph by water electrolysis

Boron doped diamond (BDD) electrodes have shown considerable promise as an electrode material where many of their reported properties such as extended solvent window, low background currents, corrosion resistance, etc., arise from the catalytically inert nature of the surface. However, if during the growth process, non-diamond-carbon (NDC) becomes incorporated into the electrode matrix, the electrochemical properties will change as the surface becomes more catalytically active. As such it is important that the electrochemist is aware of the quality and resulting key electrochemical properties of the BDD electrode prior to use. This paper describes a series of characterization steps, including Raman microscopy, capacitance, solvent window and redox electrochemistry, to ascertain whether the BDD electrode contains negligible NDC i.e. negligible sp2 carbon. One application is highlighted which takes advantage of the catalytically inert and corrosion resistant nature of an NDC-free surface i.e. stable and quantifiable local proton and hydroxide production due to water electrolysis at a BDD electrode. An approach to measuring the local pH change induced by water electrolysis using iridium oxide coated BDD electrodes is also described in detail.

Raman spectra and electrochemical characteristics were obtained for representative BDD macrodisc electrodes with different dopant densities, and both significant and negligible levels of NDC, Figures 1 and 2. Figures 1A and B show typical Raman data for NDC-containing thin film microcrystalline BDD and larger grain freestanding BDD, doped above the metallic threshold, respectively. The presence of NDC is identifiable by t...

Watch this Scientific Journal Video about Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis at JoVE.com

Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis

A protocol is described for the characterization of the key electrochemical parameters of a boron doped diamond (BDD) electrode and subsequent application for in situ pH generation experiments.

Assessment of Boron Doped Diamond Electrode Quality and Application to In Situ Modification of Local pH by Water Electrolysis

Boron doped diamond (BDD) electrodes have shown considerable promise as an electrode material where many of their reported properties such as extended ...

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