Name: assessment of boron doped diamond electrode quality and application to in situ modification of local ph by water electrolysis
Uploaded: 2016-01-06T13:00:01.000+00:00
Duration: 13 min 9 s
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 (H2SO4; ~ 2 ml or deep enough to cover the diamond) on a hot plate at RT and insert the BDD.</li>
	<li>Add potassium nitrate (KNO3) until it no longer dissolves (~ 0.5 g in 2 ml), then cover with a watch glass and heat to ~ 300 &#176;C, the solution will turn brown as it heats and the potassium nitrate will dissolve. 
	CAUTION! Care should be taken when handling hot acid; rubber gloves, safety glasses and lab coat should be worn and this process should be conducted in a fume hood.</li>
	<li>Leave to heat for at least 30 min or until there is no longer any brown color to the solution, then turn off the hot plate and leave the solution to cool to RT.</li>
	<li>Carefully dispose of the acid by diluting in RT water and rinse the BDD with distilled water.</li>
	<li>Measure the surface contact angle, see section 1.2. Hydrophobic (H-terminated)20,21 electrodes have reported contact angles in the range 60-90&#176;3, which significantly reduces as the surface is rendered hydrophilic through O-termination.</li>
	<li>(optional alternative method) For very thin film electrodes (attached to the growth substrate and to avoid film delamination using the above treatment), wash once with 2-propanol and twice with deionized water in an ultrasonic bath. Then, adopt one of the following three cleaning procedures (1) anodically polarize the diamond for 30 min at 10 mA cm-2 in 1 M perchloric acid at 40 &#176;C22; or (2) anodically polarize the diamond for 20 min at 10 mA cm-2 in 1 M nitric acid, then subsequently cathodically polarize at 10 mA cm-2 for a further 20 min in the same solution23 or; (3) cycle the diamond between 2 V in 0.1 M H2SO4 until a stable electrochemical signal is achieved7. Follow this with step 1.4.</li>
</ol>
2. Contact Angle Measurement
<ol>
	<li>Place the diamond on the sample stage of a contact angle analyzer, ensuring it is flat. Place a 1 ml syringe in the positioner above the sample stage, secure a needle on the end. Fill the syringe with deionized water.</li>
	<li>Use the z-controller to lower the syringe to the sample, use the x- and y- controllers and the camera/illuminator to align the syringe above the center of the diamond.</li>
	<li>Using the analyzer software dispense repeat 1 &#181;l volumes of water out of the syringe until a droplet forms at the tip of the needle, visible on the camera image (never more than 10 &#181;l). Lower the needle to deposit the droplet on to the surface and adjust the illumination for maximum contrast.</li>
	<li>Collect an image and apply drop shape analysis software, using the conic section method. Click &#34;find baseline&#34; in the software, and then click &#34;computation&#34; followed by &#34;tangent&#34;. 
	NOTE: this procedure detects the baseline and fits a conic equation to the (elliptical) drop shape; a contact angle, &#952;, is drawn between the baseline and the tangent at the three-phase contact point.</li>
</ol>
3. BDD Material Characterization
<ol>
	<li>Raman Analysis for sp2/sp3 content
	<ol>
		<li>Carry out Raman (see reference14 for a guide to Practical Raman Spectroscopy) in several different areas of the BDD electrode,24 use of a 514.5 nm or 532 nm laser, which emphasizes sp2 content, is advocated.</li>
		<li>Turn on the micro-Raman spectrometer and allow ~30 min for the CCD Detector to cool down. Check the appropriate lens, diffraction grating and filters are in place for use with the laser of choice.</li>
		<li>Calibrate the system using a silicon (Si) calibration sample. Place the Si substrate in the instrument chamber and focus optically on the sample with the microscope. Shut the door to the chamber. Switch to laser view and check the laser spot is well defined and circular. Calibrate using the software, click &#34;tools&#34; followed by &#34;calibration&#34; then &#34;quick calibration&#34; then &#34;ok&#34;.</li>
		<li>Remove the Si substrate from the chamber and replace with the BDD electrode. Optically focus the microscope on the area of interest, switch to laser view and open the shutter to check that the laser is focused. Close the shutter.</li>
		<li>Take a Raman measurement using the software; click &#34;measurement&#34; then &#34;new&#34; then &#34;spectral acquisition.&#34; set the measurement wavenumber range to cover the features of interest, for BDD this is 200 - 1,800 cm-1; set the scan acquisition time (&#60;10 sec); set the laser power to 100% (for BDD) and; set the number of accumulations (repeat scans) to five (for BDD). If the resulting spectrum is very noisy more accumulations may be necessary. Press run and save the resulting spectrum for analysis. Take a picture of the area Raman was performed in using the live video. Save the image as a reference.</li>
		<li>Observe the peak ~ 1,332 cm-1 in the spectrum which indicates sp3 diamond (Figure 1); the broader the peak the more defects present3,25.</li>
		<li>Observe any NDC &#8212; indicated by a broad G peak centered at 1,575 cm-1 26, in the spectra (Figure 1A and 1B), originating from the stretching of paired sp2 sites; the greater the peak intensity the more NDC present. 
		NOTE: the &#960; bonds formed by sp2 C are more polarizable than sp3 &#963; bonds and are resonantly enhanced by visible lasers, leading to broader, more dominant, G peaks25. Note that the exact method used to perform analyses may vary between different instruments and software.</li>
	</ol>
	</li>
</ol>
4. Electrochemical Characterization
<ol>
	<li>Preparing ohmic contacts
	<ol>
		<li>Freestanding BDD
		<ol>
			<li>Using standard techniques sputter (or evaporate)the backside of the BDD with titanium (Ti)/gold (Au) 10 nm/300 nm, using a sputterer/evaporator at pressures below 1 &#215; 10-5 mBar. If a three target source is available, more ideally is Ti 10 nm / platinum (Pt) 10 nm / Au 300 nm to avoid diffusion of Ti into the Au.</li>
			<li>Anneal for 5 hr at 400 &#176;C (atmospheric pressure) enabling the Ti to form titanium carbide, crucial for formation of an ohmic contact27. 
			NOTE: if the back surface of the BDD is highly polished (~ nm roughness) then it is preferably to roughen the surface prior to sputter deposition to ensure a more robust coating. This can be achieved by, for example, low power laser micromachining the surface (removing &#60; 30 &#956;m material).</li>
		</ol>
		</li>
		<li>Thin film diamond grown on a conducting substrate
		<ol>
			<li>Sputter/evaporate as above, but to the top face, using a shadow mask gently place on the top surface to avoid top contacting the entire electrode. 
			OR</li>
			<li>Scratch the back of the conducting substrate using a diamond tipped pen. Then coat the scratched area with conducting Ag paste or a similar conductive paint by painting on a thin layer with a small paintbrush. Finally, electrically connect by attaching copper wires with conductive epoxy. 
			NOTE: there are a variety of ways to prepare the BDD after electrical contact as described in reference 4, e.g. if the BDD can be machined into smaller structures, seal in glass or epoxy, or if still attached to the wafer clamp/attach an electrochemical cell to the top surface.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Capacitance Measurements
	<ol>
		<li>Prepare a 20 ml of 0.1 M KNO3 solution by weighing 0.20 g in doubly distilled water (this water quality is recommended throughout, resistivity 18.2 M cm). Clean the electrode prior to use either by alumina polishing or by electrochemically cycling in dilute acid (see section 1 NOTE)16,23,28.</li>
		<li>Using a potentiostat run cyclic voltammograms (CVs) at 0.1 V sec-1 between -0.1 V and 0.1 V, starting at 0 V, with the BDD as the working electrode versus a common reference electrode, e.g. silver/silver chloride (Ag/AgCl) or a saturated calomel electrode (SCE), and a Pt counter electrode. Analyze the second CV. 
		NOTE: Figure 2A shows a typical capacitance curve recorded with a freestanding metallic doped BDD electrode.</li>
		<li>Measure the total current magnitude at 0 V from the recorded capacitance curve and divide by 2, this value is &#34;i&#34;. Determine the capacitance, C, using the value for i, with equation 1, normalize with respect to electrode area (accounting for surface roughness if appropriate) and quote in &#181;F cm-2. High quality, &#34;metal-like&#34; BDD has a capacitance &#60;&#60; 10 &#181;F cm-2. Use any data plotting software to present and analyze the data. 
		i = C(Vt-1)&#160;&#160; (eq. 1); 
		where i is current (A) and (V t-1) is the potential scan rate.</li>
	</ol>
	</li>
	<li>Solvent Window
	<ol>
		<li>Clean the electrode as in step 4.2.1. Using a potentiostat run a CV in 0.1 M KNO3 at 0.1 V sec-1 from 0 V to -2 V then between -2 V and +2 V and back to 0 V with the BDD as the working electrode vs. a common reference electrode and Pt counter electrode. Repeat. Analyze the second CV, an example CV is shown in Figure 2B.</li>
		<li>Convert current to current density (mA cm-2), taking surface roughness into account, and quote the solvent window as the potential window defined by current limits of &#177;0.4 mA cm-2 in both directions.7,29 Use any data plotting software to present and analyze the data.</li>
		<li>Observe the evidence of NDC (sp2 carbon) in the solvent window; the oxygen reduction reaction is favored on NDC that is clearly evident in the reductive window. Oxidation of sp2 containing groups also results in characteristic peaks just before water electrolysis in the anodic window (Figure 2B). 
		NOTE: high quality &#34;metallic&#34; BDD electrodes have solvent windows &#62;&#62; 3 V, do not support the oxygen reduction reaction (ORR) in 0.1 M KNO3 (or ORR is strongly kinetically retarded) and show negligible NDC oxidation signatures.</li>
	</ol>
	</li>
	<li>Redox Electrochemistry
	<ol>
		<li>Clean the electrode as in step 4.2.1.</li>
		<li>Using a potentiostat record CVs in 1 mM ruthenium hexaamine (Ru(NH3)63+) and 0.1 M KNO3 between +0.2 V and -0.8 V versus SCE, for scan rates in the range 0.05 V sec-1- 0.2 V sec-1. 
		NOTE: This couple shows fast electron transfer and is electroactive in a region which challenges p-type semiconducting BDD. sp2 containing BDD will also show ORR in this region, the signal for the latter is more evident as the concentration of Ru(NH3)63+ is decreased.</li>
		<li>Measure the voltage separation between the anodic and cathodic peak current (&#916;Ep) from the recorded CV, and the temperature as described20. For &#34;metal-like&#34; ohmically contacted oxygen-terminated BDD at 298 K, &#916;Ep &#60; 70 mV30,31. Larger &#916;Ep values are symptomatic of a poor ohmic contact or a lower boron content, as shown in Figure 2C for BDD electrodes of dopant densities in the range 9.2 &#215; 1016 to 3 &#215; 1020 B atoms cm-3.</li>
		<li>Measure the peak current of the forward scan, ip, and correlate with that expected from the Randles Sevcik equation 2 (quoted at 298 K)3,30, assuming the electrode is disk-shaped in geometry and large enough (diameter 1 mm) that linear diffusion dominates. Use any data plotting software to present and analyze the data. 
		ip = 2.69 &#215; 105 n3/2 AD1/2 cv1/2&#160;&#160; (eq 2) 
		where n is the number of electrons transferred, A is area (cm2), D is diffusion coefficient (cm2 sec-1), c is concentration (mol cm-3) and v is scan rate (V sec-1).</li>
	</ol>
	</li>
</ol>
5. pH Generation: Preparation of pH Sensitive Electrode and pH Generation
<ol>
	<li>Iridium Oxide (pH sensitive) Solution Preparation
	<ol>
		<li>Prepare a 20 ml 0.1 M KNO3 solution as in section 5.4.1. Add 5 drops of phenolphthalein indicator solution using a Pasteur pipette and stir (this is sufficient to see a response by eye, but for a more intense color, add more drops). Place the BDD working electrode and Pt counter electrode in solution.</li>
		<li>Adjust pH of the solution to 10.5 by addition of anhydrous potassium chloride salt, stirring continuously. Leave covered and stirring for 48 hr at RT to stabilize, at this stage the solution will gradually go from yellow-green to blue-purple. Store in a refrigerator at 3 &#176;C.</li>
	</ol>
	</li>
	<li>pH Sensitive Iridium Oxide Film Deposition
	<ol>
		<li>Using a potentiostat run a CV in the iridium oxide solution between 0 V and +1 V versus SCE to determine the potential at which the maximum current is recorded. This is the deposition potential, Edep as shown in Figure 3A, typically lying between ~+0.6 V &#8211; +0.85 V; it can vary depending on a number of factors such as temperature, electrode material etc.32,33</li>
		<li>Using chronoamperometry with a potentiostat, step the potential from 0 V (&#34;initial E&#34; and &#34;Low E&#34; in the software), where no electrolysis occurs to Edep (&#34;High E&#34; in the software), for a time period of 0.2 sec per step, repeat 100x.</li>
		<li>Run a CV between 0 V and +1 V in 0.1 M H2SO4 for the IrOx deposited electrode. The characteristic CV shape is shown in Figure 3B. A current density in the range ~ 0.6 mA cm-2 - 0.7 mA cm-2 for the first anodic peak (corresponding to an average film thickness of ~ 8 nm for 0.7 mA cm-2), indicates a stable pH sensitive film34,35.</li>
		<li>If the current density is less than 0.6 mA cm-2 repeat steps 5.2.2 - 5.2.4 until this value is reached. Leave the electrode in pH 7 buffer solution for 24 hr to hydrate as the response of the IrOx film is hydration-dependant33.</li>
	</ol>
	</li>
	<li>IrOx Film pH Characterization
	<ol>
		<li>Prepare a series of buffer solutions which cover the pH range of interest (pH 2 - pH 12), these can be made in house (e.g. Carmody36) or purchased commercially.</li>
		<li>Rinse the electrode with distilled water. Place the IrOx electrode and reference electrode in the buffer solution of lowest pH. Using a potentiostat record the open circuit potential (OCP) over 30 sec, with three repeats. Remove the electrode from the solution, rinse and place in the next buffer.</li>
		<li>Repeat step 5.3.2 for each buffer, then repeat the series at least twice. Plot pH vs. OCP, the calibration plot for the film response. An IrOx film exhibits a slope with a gradient between 59 - 80 mV per decade37. 
		NOTE: Figure 3C shows an example calibration plot for a successful IrOx pH sensor on BDD.</li>
	</ol>
	</li>
	<li>Using a pH generator and measurement system 
	NOTE: this assumes use of a dual electrode system where one electrode is coated with the IrOx film (e.g. disc) and the second (e.g. BDD ring) will generate H+ or OH- galvanostatically from water electrolysis.
	<ol>
		<li>Prepare a 20 ml 0.1 M KNO3 solution by adding deionized water to the salt. Connect the IrOx coated electrode as the working electrode in a two electrode system, with the second electrode a stable reference electrode e.g. SCE. Measure the OCP using a potentiostat, to establish the starting pH.</li>
		<li>Connect the generator electrode to a suitable two electrode galvanostatic system with a counter electrode, e.g. Pt foil, and repeat step 5.4.1, but after a defined period of time apply a current to the generator electrode. 
		NOTE: we find currents in the range 0 to &#177; 50 &#956;A are suitable with our BDD electrodes; larger currents result in appreciable gas evolution. The magnitude and direction of the current depends on the desired result; a positive current will result in a shift to more acidic pH and a negative current to more alkaline pH, the larger the current the greater the pH change.</li>
		<li>Using the potentiostat, record the change in OCP in response to the galvanostatic current, wait until the response stabilizes. Then place the IrOx electrode in pH 7 buffer for 10 min to re-equilibrate the IrOx film.</li>
		<li>Repeat steps 5.4.2 to 5.4.3 with different applied currents, until all the data required has been collected. Plot the data using the calibration curve obtained in section 5.3 to convert OCP to pH, an example data set is shown in Figure 4A. Remove the IrOx film using alumina polishing or pulsing in 0.1 M H2SO4 from +2 V to -2 V for 0.2 sec, &#215;100. Apply to the measurement system of interest.</li>
	</ol>
	</li>
	<li>Visual assessment of local pH generation
	<ol>
		<li>Prepare a 20 ml 0.1 M KNO3 solution as in section 5.4.1. Add 5 drops of phenolphthalein indicator solution using a Pasteur pipette and stir (this is sufficient to see a response by eye, but for a more intense color, add more drops). Place the BDD working electrode and Pt counter electrode in solution.</li>
		<li>Apply a negative current to the working electrode using a galvanostat as in step 5.4.2 (e.g. ~ -0.6 mA cm-2) such that the solution changes color from colorless to pink. This now locally generates a solution which is at pH &#8805; 10.5.</li>
		<li>Repeat step 5.5.1 with 5 drops of methyl red solution instead of phenolphthalein and stir. Apply a sufficiently positive current (e.g. ~ 6.6 mA cm-2) such that the solution changes color from yellow to red. This now locally generates a solution which is at pH &#8804; 4.238.</li>
	</ol>
	</li>
</ol>

The authors declare that they have no competing financial interests.

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.

<table><tbody><tr><td>Pt Wire</td><td></td><td></td><td>Counter Electrode</td></tr><tr><td>Saturated Calomel Electrode</td><td>IJ Cambria Scientific Ltd.</td><td>2056</td><td>Reference Electrode (alternatively use Ag|AgCl)</td></tr><tr><td>BDD Electrode</td><td></td><td></td><td>Working Electrode</td></tr><tr><td>Iridium Tetrachloride</td><td>VWR International Ltd</td><td>12184.01</td><td></td></tr><tr><td>Hydrogen Peroxide</td><td>Sigma-Aldrich</td><td>H1009</td><td>(30% w/w) Corrosive</td></tr><tr><td>Oxalic Acid&amp;nbsp;</td><td>Sigma-Aldrich</td><td>241172</td><td>Harmful, Irritant</td></tr><tr><td>Anhydrous Potassium Chloride</td><td>Sigma-Aldrich</td><td>451029</td><td></td></tr><tr><td>Sulphuric Acid</td><td>VWR International Ltd</td><td>102765G</td><td>(98%) Corrosive</td></tr><tr><td>Potassium Nitrate</td><td>Sigma-Aldrich</td><td>221295</td><td></td></tr><tr><td>Hexaamine Ruthenium Chloride</td><td>Strem Chemicals Inc.</td><td>44-0620</td><td>Irritant</td></tr><tr><td>Perchloric Acid</td><td>Sigma-Aldrich</td><td>311421</td><td>Oxidising, Corrosive</td></tr><tr><td>2-Propanol</td><td>Sigma-Aldrich</td><td>24137</td><td>Flammable</td></tr><tr><td>Nitric Acid</td><td>Sigma-Aldrich</td><td>695033</td><td>Oxidising, Corrosive</td></tr><tr><td>Sputter/ Evapourator</td><td></td><td></td><td>With Ti &amp;amp; Au targets</td></tr><tr><td>Raman</td><td></td><td></td><td>514.5 nm laser</td></tr><tr><td>Annealing Oven</td><td></td><td></td><td>Capable of 400 &amp;deg;C</td></tr><tr><td>Ag paste</td><td>Sigma-Aldrich</td><td>735825</td><td>or other conductive paint</td></tr><tr><td>Potentiostat</td><td></td><td></td><td></td></tr><tr><td>pH Buffer solutions</td><td>Sigma-Aldrich</td><td>38740-38752</td><td>Fixanal buffer concentrates</td></tr><tr><td>Phenolphthalein Indicator</td><td>VWR International Ltd</td><td>210893Q</td><td></td></tr><tr><td>Methyl Red Indicator</td><td>Sigma-Aldrich</td><td>32654</td><td></td></tr></tbody></table>

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 ...

assessment-boron-doped-diamond-electrode-quality-application-to-situ

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14.7K Views.  University of Warwick. 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.

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

Electrochemically and Bioelectrochemically Induced Ammonium Recovery

Streams such as urine and manure can contain high levels of ammonium, which could be recovered for reuse in agriculture or chemistry. The extraction of ammonium from an ammonium-rich stream is demonstrated using an electrochemical and a bioelectrochemical system. Both systems are controlled by a potentiostat to either fix the current (for the electrochemical cell) or fix the potential of the working electrode (for the bioelectrochemical cell). In the bioelectrochemical cell, electroactive bacteria catalyze the anodic reaction, whereas in the electrochemical cell the potentiostat applies a higher voltage to produce a current. The current and consequent restoration of the charge balance across the cell allow the transport of cations, such as ammonium, across a cation exchange membrane from the anolyte to the catholyte. The high pH of the catholyte leads to formation of ammonia, which can be stripped from the medium and captured in an acid solution, thus enabling the recovery of a valuable nutrient. The flux of ammonium across the membrane is characterized at different anolyte ammonium concentrations and currents for both the abiotic and biotic reactor systems. Both systems are compared based on current and removal efficiencies for ammonium, as well as the energy input required to drive ammonium transfer across the cation exchange membrane. Finally, a comparative analysis considering key aspects such as reliability, electrode cost, and rate is made.
This video article and protocol provide the necessary information to conduct electrochemical and bioelectrochemical ammonia recovery experiments. The reactor setup for the two cases is explained, as well as the reactor operation. We elaborate on data analysis for both reactor types and on the advantages and disadvantages of bioelectrochemical and electrochemical systems.

We demonstrate the extraction of ammonium from an ammonium-rich stream using an electrochemical and a bioelectrochemical system. The reactor setup, operation and data analysis are discussed.

Streams such as urine and manure can contain high levels of ammonium, which could be recovered for reuse in agriculture or chemistry. The extraction of ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Engineering

Self-standing Electrochemical Set-up to Enrich Anode-respiring Bacteria On-site

Anaerobic respiration coupled with electron transport to insoluble minerals (referred to as extracellular electron transport [EET]) is thought to be critical for microbial energy production and persistence in many subsurface environments, especially those lacking soluble terminal electron acceptors. While EET-capable microbes have been successfully isolated from various environments, the diversity of bacteria capable of EET is still poorly understood, especially in difficult-to-sample, low energy or extreme environments, such as many subsurface ecosystems. Here, we describe an on-site electrochemical system to enrich EET-capable bacteria using an anode as a respiratory terminal electron acceptor. This anode is connected&#160;to a cathode capable of&#160;catalyzing abiotic oxygen reduction. Comparing this approach with electrocultivation methods that use a potentiostat for poising the electrode potential, the two-electrode system does not require an external power source. We present an example of our on-site enrichment utilized in an alkaline pond at the Cedars, a terrestrial serpentinization site in Northern California. Prior attempts to cultivate mineral reducing bacteria were unsuccessful, which is likely due to the low-biomass nature of this site and/or the low relative abundance of metal reducing microbes. Prior to implementing our two-electrode enrichment, we measured the vertical profile of dissolved oxygen concentration. This allowed us to place the carbon felt anode and platinum-electroplated carbon felt cathode at depths that would support anaerobic and aerobic processes, respectively. Following on-site incubation, we further enriched the anodic electrode in the laboratory and confirmed&#160;a distinct microbial community compared to the surface-attached or biofilm communities normally observed at the Cedars. This enrichment subsequently led to the isolation of the first electrogenic microbe from the Cedars. This method of on-site microbial enrichment has the potential to greatly enhance the isolation of EET-capable bacteria from low biomass or difficult to sample habitats.

On-site microbial enrichment or in situ cultivation techniques can facilitate the isolation of difficult-to-culture microbial taxa, especially from low-biomass or geochemically extreme environments. Here, we describe an electrochemical set-up without using an external power source to enrich microbial strains that are capable of extracellular electron transport (EET).

Anaerobic respiration coupled with electron transport to insoluble minerals (referred to as extracellular electron transport [EET]) is thought to be ...

Environment

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

In Situ Lithiated Reference Electrode: Four Electrode Design for In-operando Impedance Spectroscopy

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate multiple processes responsible for long-term performance decay. Given the complexity of physical processes occurring inside the cell, it is often challenging to achieve a full understanding of the root causes of this performance degradation. This difficulty arises in part from the fact that any electrochemical measurement of a battery will return the combined contributions of all components in the cell. Incorporation of a reference electrode can solve part of the problem, as it allows the electrochemical reactions of the cathode and the anode to be individually probed. A variation in the voltage range experienced by the cathode, for example, can indicate alterations in the pool of cyclable lithium ions in the full-cell. The structural evolution of the many interphases existing in the battery can also be monitored, by measuring the contributions of each electrode to the overall cell impedance. Such wealth of information amplifies the reach of diagnostic analysis in Li-ion batteries and provides valuable input to the optimization of individual cell components. In this work, we introduce the design of a test cell able to accommodate multiple reference electrodes, and present reference electrodes that are appropriate for each specific type of measurement, detailing the assembly process in order to maximize the accuracy of the experimental results.

The incorporation of reference electrodes in a Li-ion battery provides valuable information to elucidate degradation mechanisms at high voltages. In this article, we present a cell design that accommodates multiple reference electrodes, along with the assembly steps to assure maximum accuracy of the data obtained in electrochemical measurements.

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate ...

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in an aqueous and an organic solution. Cyclic voltammetry (CV) was used in the synthesis of PEDOT thin layers. Lithium perchlorate (LiClO4) was used as a dopant in both aqueous (aqueous/acetonitrile (ACN)) and organic (propylene carbonate (PC)) solvent systems. After the PEDOT layer was created in the organic system, the electrode surface was acclimatized by successive cycling in an aqueous solution for use as a sensor for aqueous samples. 
The use of an aqueous-based electropolymerization method has the potential benefit of removing the acclimatization step to have a shorter sensor preparation time. Although the aqueous method is more economical and environmentally friendly than the organic solvent method, superior PEDOT formation is obtained in the organic solution. The resulting PEDOT electrode surfaces were characterized by scanning electron microscopy (SEM), which showed the constant growth of PEDOT during electropolymerization from the organic PC solution, with rapid fractal-type growth on gold (Au) microelectrodes.

Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

We describe aqueous and organic solvent systems for the electropolymerization of poly(3,4-ethylenedioxythiophene) to create thin layers on the surface of gold microelectrodes, which are used for sensing low molecular weight analytes.

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of ...

Manufacturing of a Nafion-coated, Reduced Graphene Oxide/Polyaniline Chemiresistive Sensor to Monitor pH in Real-time During Microbial Fermentation

Here, we report the engineering of a solid-state micro pH sensor based on polyaniline-functionalized, electrochemically reduced graphene oxide (ERGO-PA). Electrochemically reduced graphene oxide acts as the conducting layer and polyaniline acts as a pH-sensitive layer. The pH-dependent conductivity of polyaniline occurs by doping of holes during protonation and by the dedoping of holes during deprotonation. We found that an ERGO-PA solid-state electrode was not functional as such in fermentation processes. The electrochemically active species that the bacteria produce during the fermentation process interfere with the electrode response. We successfully applied Nafion as a proton-conducting layer over ERGO-PA. The Nafion-coated electrodes (ERGO-PA-NA) show a good sensitivity of 1.71 &#937;/pH (pH 4 - 9) for chemiresistive sensor measurements. We tested the ERGO-PA-NA electrode in real-time in the fermentation of Lactococcus lactis. During the growth of L. lactis, the pH of the medium changed from pH 7.2 to pH 4.8 and the resistance of the ERGO-PA-NA solid-state electrode changed from 294.5 &#937; to 288.6 &#937; (5.9 &#937; per 2.4 pH unit). The pH response of the ERGO-PA-NA electrode compared with the response of a conventional glass-based pH electrode shows that reference-less solid-state microsensor arrays operate successfully in a microbiological fermentation.

Here, we report the protocol for the fabrication of a Nafion-coated, polyaniline-functionalized, electrochemically reduced graphene oxide chemiresistive micro pH sensor. This chemiresistor-based, solid-state micro pH sensor can detect pH changes in real-time during a Lactococcus lactis fermentation process.

Here, we report the engineering of a solid-state micro pH sensor based on polyaniline-functionalized, electrochemically reduced graphene oxide (ERGO-PA). ...

Bioengineering

Chronoamperometry Analysis of EET in Lactiplantibacillus plantarum with DHNA

Characterizing Mediated Extracellular Electron Transfer in Lactic Acid Bacteria with a Three-Electrode, Two-Chamber Bioelectrochemical System

Many bacteria perform extracellular electron transfer (EET), whereby electrons are transferred from the cell to an extracellular terminal electron acceptor. This electron acceptor can be an electrode and electrons can be delivered indirectly via a redox-active mediator molecule. Here, we present a protocol to study mediated EET in Lactiplantibacillus plantarum, a probiotic lactic acid bacterium widely used in the food industry, using a bioelectrochemical system. We detail how to assemble a three-electrode, two-chambered bioelectrochemical system and provide guidance on characterizing EET in the presence of a soluble mediator using chronoamperometry and cyclic voltammetry techniques. We use representative data from 1,4-dihydroxy-2-naphthoic acid (DHNA)-mediated EET experiments with L. plantarum to demonstrate data analysis and interpretation. The techniques described in this protocol can open new opportunities for electro-fermentation and bioelectrocatalysis. Recent applications of this electrochemical technique with L. plantarum demonstrated an acceleration of metabolic flux towards producing fermentation end-products, which are critical flavor components in food fermentation. As such, this system has the potential to be further developed to alter flavors in food production or produce valuable chemicals.

Here we present a protocol for characterizing mediated extracellular electron transfer (EET) in lactic acid bacteria using a three-electrode, two-chamber bioelectrochemical system. We illustrate this method with Lactiplantibacillus plantarum and the redox mediator 1,4-dihydroxy-2-naphthoic acid and provide a thorough description of the electrochemical techniques used to evaluate mediated EET.

Many bacteria perform extracellular electron transfer (EET), whereby electrons are transferred from the cell to an extracellular terminal electron ...

Biochemistry

Electrochemical Measurements of Supported Catalysts Using a Potentiostat/Galvanostat

Source: Laboratory of Dr. Yuriy Rom&#225;n &#8212; Massachusetts Institute of Technology
A potentiostat/galvanostat (often referred to as simply a potentiostat) is an instrument that measures current at an applied potential (potentiostatic operation) or measures potential at an applied current (galvanostatic operation) (Figure 1). It is the most commonly used instrument in the electrochemical characterization of anode and cathode materials for fuel cells, electrolyzers, batteries, and supercapacitors.
Conventionally, these anode and cathode materials are interfaced with a potentiostat via a three-electrode electrochemical cell. The electrode leads from the potentiostat are connected to the reference electrode, the counter electrode (often called the auxiliary electrode), and the working electrode (which contains the test material of interest). The electrochemical cell is then filled with a high ionic strength electrolyte solution, such as an acidic, alkaline, or salt solution. The media for this high ionic strength solution is typically aqueous; however, for applications necessitating higher operating cell potential windows, such as batteries and supercapacitors, non-aqueous media is often used. The cell media is degassed with an inert gas (to prevent unwanted side reactions) or with a test gas (if the test reaction involves a gas at one of the electrodes).
Alternatively, a salt bridge or membrane is employed to maintain ionic contact if the two half cells are to be measured in different electrolytes. In heterogeneous electrocatalysis, this type of &#34;two compartment&#34; cell is often used if the test molecule at the working electrode is also reactive at the counterelectrode. This happens frequently as the counterelectrode typically employed is platinum, which is a highly active catalyst for many reactions. Here, single compartment cells will be used, where all three electrodes are in the same media.
This video will explain the process of polishing a working electrode, preparing a catalyst ink, mounting the catalyst ink onto the working electrode, preparing the electrochemical cell, and then performing electrochemical measurements. The measurements that are performed include: cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronopotentiometry (CP), and chronoamperometry (CA).
<img alt="Figure 1" src="/files/ftp_upload/5698/5698fig1.jpg" /> 
Figure 1. An example of a single compartment electrochemical cell. a.) Teflon cap, b.) glass cell, c.) Pt wire counter electrode, d.) working electrode, e.) Ag/AgCl reference electrode, f.) 0.5 M aqueous sulfuric acid electrolyte solution.

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

Summary

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Chapters in this video

Electrochemically and Bioelectrochemically Induced Ammonium Recovery

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

Self-standing Electrochemical Set-up to Enrich Anode-respiring Bacteria On-site

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

In Situ Lithiated Reference Electrode: Four Electrode Design for In-operando Impedance Spectroscopy

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

Manufacturing of a Nafion-coated, Reduced Graphene Oxide/Polyaniline Chemiresistive Sensor to Monitor pH in Real-time During Microbial Fermentation

Characterizing Mediated Extracellular Electron Transfer in Lactic Acid Bacteria with a Three-Electrode, Two-Chamber Bioelectrochemical System

Electrochemical Measurements of Supported Catalysts Using a Potentiostat/Galvanostat