The authors gratefully acknowledge the financial support of "Excilight" project "Donor-Acceptor Light Emitting Exciplexes as Materials for Easy-to-tailor Ultra-efficient OLED Lightning" (H2020-MSCA-ITN-2015/674990) financed by Marie Sk&#322;odowska-Curie Actions within the framework programme for research and innovations "Horizon-2020".

1. Basic Preparation of an Electrochemical Experiment
<ol>
	<li>Prepare 4 mL of a working solution containing 0.1 mol&#8729;L&#8722;1 Bu4NBF4 and 0.001 mol&#8729;L&#8722;1 investigated organic compound by adding calculated amounts of solid powders into 4 mL of dichloromethane in a small vessel or a test tube. With 2,8-bis(3,7-dibutyl-10H-phenoxazin-10- yl)dibenzo[b,d]thiophene-S,S-dioxide (molar mass 802 g&#8729;mol&#8722;1), weigh 3.208 mg of this compound and 0.1645 g of Bu4NBF4.</li>
	<li>Fill a 3 mL electrochemical cell with 2 mL of solution using a pipette. The remaining portion of the solution will be needed later for impedance measurement and reproducing the results.</li>
	<li>Polish a 1 mm diameter platinum working disc electrode (WE) for 30 s using a polishing cloth moistened by several drops of alumina slurry. Rub the flat surface of the disc electrode with a piece of cloth mounted on an immobile support (e.g. Petri dish) by applying moderate pressure.</li>
	<li>Rinse the electrode with distilled water three times to remove alumina particles.</li>
	<li>Anneal a counter electrode (CE, platinum wire) in a butane burner flame. Carefully put the platinum wire in a flame for less than 1 s and quickly remove when it starts reddening to avoid melting. 
	&#8203;NOTE: The CE surface area is not stipulated but must be much higher than the surface area of the working electrode. In this case, impedance of working electrode interface would have the major impact on the total system impedance and would permit excluding counter electrode impedance from consideration.
	<ol>
		<li>Anneal a reference electrode (RE, silver wire) in butane burner flame in the same manner.</li>
	</ol>
	</li>
	<li>Put all three electrodes (working, counter and reference) into a cell avoiding mutual contact and connect to the corresponding potentiostat cables marked as WE, CE and RE. Insert a gas delivering tube connected with argon gas bottle for further deaeration.</li>
	<li>Open the gas valve and deaerate solution by bubbling argon through the solution for 20 min. Close the gas valve before measurement.</li>
</ol>
2. Tentative Characterization by Cyclic Voltammetry (CVA)
<ol>
	<li>Register the CVA of the working solution within a potential range from &#8722;2.0 V to +2.0 V and scan rate 100 mV&#8729;s&#8722;1.
	<ol>
		<li>Launch the program Cyclic voltammetry in the potentiostat software.</li>
		<li>Choose 0.0 V as initial potential value, &#8722;2.0 V as minimal potential, +2.0 V as maximal scanning potential, 100 mV&#8729;s&#8722;1 as scanning rate. Other parameters are optional.</li>
		<li>Click the button Start. 
		NOTE: A typical voltammogram is presented in Figure 1.</li>
	</ol>
	</li>
	<li>Determine the potential value from the CVA obtained. Note the potential values when maxima of positive (anodic peak) and negative (cathodic peak) current appear and calculate the average value.</li>
	<li>Add 10 mg of ferrocene by spatula into the working solution and deaerate it by argon bubbling for 5 min. This is necessary for mixing and complete dissolution of the ferrocene added. 
	NOTE: The ferrocene amount is not precise. However, adding less than 1 mg or more than 20 mg would complicate estimation of equilibrium potential.</li>
	<li>Register the CVA of the working solution within the potential range from &#8722;1.0 V to +1.0 V and scan rate 100 mV&#8729;s&#8722;1. A small reversible peak of ferrocene will appear as shown in Figure 1.</li>
	<li>Determine the potential value of ferrocene reversible oxidation from the CVA obtained. Note the potential values when maxima of positive (anodic peak) and negative (cathodic peak) current appear and calculate the average value.</li>
	<li>Put another portion of the solution prepared at step 1.1 into the cell and clean the electrodes by repeating the procedure described in 1.2-1.7.</li>
</ol>
3. Registration of Impedance Spectrum
NOTE: An example of the setup in software is shown in Figure 2; any other software or device also can be used. However, the setup arrangement may differ in different software, although the main principles remain the same. Use the EIS in a staircase mode, i.e. potentiostatic spectra are registered automatically one after another.
<ol>
	<li>In the software, choose a potential range of 0.2 V covering the reversible peak in CVA. Example: A reversible oxidation peak was detected on CV at 0.7 V. The potential range for CV should be then from 0.6 V to 0.8 V. The spectra will be registered with the increment of 0.01 V, i.e. at 0.61 V, 0.62 V, etc.</li>
	<li>Register the EIS automatic measurement procedure under following conditions advised.
	<ol>
		<li>Enter the following input values: initial potential 0.6 V; finish potential 0.8 V; potential increment: 0.01 V; frequency range: from 10 kHz through 100 Hz; the number of frequencies in logarithmic scale: 20; wait for a time between the spectra: 5 s, ac voltage amplitude 10 mV, minimal 2 measures per frequency.</li>
		<li>Click the button Start. 
		NOTE: In that case, 21 spectra, each containing 41 frequency points will be obtained. The typical set of automatically registered spectra is presented in Figure 3.</li>
	</ol>
	</li>
</ol>
4. Analysis of Impedance Spectrum
<ol>
	<li>Launch the program EIS spectrum analyser.</li>
	<li>Download the spectrum by choosing File | Open.</li>
	<li>In the right upper sub-window construct an EEC by using left/right mouse click choosing series or parallel connection and necessary element from the context menu: C - capacitor, R - resistor, W - Warburg element. Start from the simplest circuit (Figure 5c).</li>
	<li>Choose initial minimal and maximal values for parameters by left-mouse-clicking table cells and entering values: C1 - from 1&#8729;10-7 to 1&#8729;10-8, R1 - from 2000 to 100, R2 - from 1000 to 100, Aw - from 50000 to 10000.</li>
	<li>Fit the model by choosing Model | Fit. Repeat the procedure several times (usually about 5 times) until the calculated values no longer change. Parameter values are shown in a table in the upper left sub-window.</li>
	<li>Check parameter errors shown in the last column of the table. If an error of a parameter exceeds 100%, that means that the parameter is not necessary for a circuit. In that case try another equivalent circuit. 
	NOTE: If one tries to fit an experimental spectrum corresponding to the simple circuit (Figure 5c) by a more complicated circuit (Figure 5a), then errors of unnecessary additional parameters W and R3 would be considerably high.</li>
	<li>Check the values of r2(parametric) and r2(amplitude) presented in the lower right sub-window. If they exceed limit 1&#8729;10&#8722;2, repeat the procedures 4.2&#8722;4.5 using another equivalent electrical circuit (EEC) (Figure 5).</li>
	<li>Repeat the procedure 4.1-4.7 for all the spectra registered</li>
	<li>For each spectrum analyzed, write down the calculated value of charge transfer resistance and the corresponding potential that the spectrum was registered at.</li>
</ol>
5. Calculation of Redox Rate Constants
<ol>
	<li>Put the values of the estimated inverse charge transfer resistance versus potential. A typical potential plot of inverse charge transfer resistance for the reversible process is presented in&#160;Figure 6.
	<ol>
		<li>Open an empty sheet of spreadsheet software.</li>
		<li>Manually enter the values of potentials and corresponding values of reverse charge transfer resistance in columns A and B.</li>
		<li>Select the range A1:B21 and choose Insert | Graph | Pointed by mouse clicking in the task menu.</li>
	</ol>
	</li>
	<li>Plot the values of a theoretical function calculated by the formula (1) on the same plot. Use constant values: F = 96485 C&#8729;mol&#8722;1, c0 = 0.01 mol&#8729;&#8722;1, z = 1, R = 8.314 J&#8729;mol&#8722;1&#8729;K&#8722;1, &#945;&#160;= 0.5, T&#160;- ambient temperature. Use the previously estimated value (3.1) of E0. 
	<img alt="Equation 1" src="/files/ftp_upload/56611/56611eq1.jpg" /> (1) 
	<img alt="Equation 2" src="/files/ftp_upload/56611/56611eq2.jpg" /> (2) 
	where Rct&#8722;1 is inverse value of charge transfer resistance normalized by surface area; z- number of electrons transferred in one step (accepted being equal 1); F- Faraday constant; c0- concentration of investigated compound; &#945; - charge transfer coefficient (accepted being equal 0.5); E- electrode potential; parameter &#952; was introduced to simplify the final formula relating E and Rct.
	<ol>
		<li>Copy the first column of values (potential values) in the same sheet in column D.</li>
		<li>Enter the constant values of F, c0, z, R, &#945;, T, E0, k0 enlisted above into cells C1:C8. Use values E0 = 0, k0 = 1&#8729;10&#8722;5.</li>
		<li>Enter formula (2) to calculate &#952; into cell E1: =EXP($C$1*$C$3/($C$4*$C$6)*(D1-$C$7)).</li>
		<li>Copy the formula into cells E2:E21 by selecting E1, clicking Copy, selecting range E2:E21 and clicking Paste.</li>
		<li>Enter formula (1) into cell F1: = $C$8*$C$1^2*$C$3^2/($C$4*$C$6)*$C$2*E1^(1-$C$5)/(1+E1).</li>
		<li>Copy the formula into cells F2:F21 by selecting F1, clicking Copy, selecting range F2:F21 and clicking Paste.</li>
		<li>Left click on the graph built at step 5.1, choose Choose data, then Add and add new data set by specifying entering D1:D21 as x range and F1:F21 as y range. 
		NOTE: Two graphs: experimental and simulated automatically marked by different colors will appear on one coordinate plot.</li>
	</ol>
	</li>
	<li>Optimize the theoretical function (1) in order to fir experimental data by varying values of equilibrium potential (E0) and standard rate constant (k0), being the target parameter. 
	&#8203;NOTE: Change of the values in cells C7 (E0) and C8 (k0) would immediately cause change of the simulated graph.
	<ol>
		<li>Change values in cells C7 and C8 manually in order to achieve equality between experimental and simulated graph. 
		NOTE: Change of E0 moves the bell-like curve along the x axis. Change of k0 controls the height of the bell-like curve. Thus, varying those two only parameters can be used to find a theoretical model corresponding to experimental results (Figure 6). Parameter &#945; (1) controls symmetry of theoretical peak. However, in real systems asymmetry may be caused by the occurrence of side-process rather than by &#945;. Since it influences resulting k0 value we recommend not to manipulate &#945; value and leave it to equal 0.5.</li>
	</ol>
	</li>
</ol>

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Instrumentation and Electroanalytical Chemistry. , (2003).</li></ol>

The authors have nothing to disclose.

This part of the work will be devoted to an explanation of chosen experimental conditions and discussion of possible applications of the method presented.
Analysis of impedance spectrum may be performed by various software. Here the basic recommendations for EEC analysis method are discussed. One needs to know that there are numerous fitting algorithms and various ways of error estimation. We present an example of using open access software developed by A. Bondarenko and G. Ragoisha24 (Figure 4).
Exact estimation of Rct value was the main objective of the work. One of the reasons for the choice of the experimental conditions was an intention to conceal the impact of diffusion. Thus, the solution concentration had to be as high as possible. While acquiring the experimental results shown here, the concentration was limited due to economic reasons. The range of frequencies from 10 kHz to 100 Hz was chosen to eliminate the effect of diffusion as well. Diffusion impedance is inversely proportional to the frequency while resistance is not dependent on the frequency. The effect of resistance in the high-frequency part of the spectrum was higher than in the low-frequency part. Spectra were not registered at the frequencies lower than 100 Hz because these data would be useless for resistance calculation. All the electrochemical results obtained in non-aqueous solvent are presented versus ferrocene-oxidized / ferrocene coupled equilibrium potential. For this reason, steps 2.3 - 2.5 are performed.
We considered EIS application to organic molecules characterization. Analysis of other EEC parameters and their potential dependencies in perspective may lead to the revelation of other effects and electrochemical characterization of compounds in solution. Estimation of redox rate constants is useful for describing the kinetics of electroactive compound reduction or oxidation and predicting material behavior in oxidizing or reducing medium.

Redox rate of the electroactive compound is an important parameter characterizing its ability to undergo oxidation or reduction processes and predict its behavior in the presence of strong oxidizing or reducing agents or under applied potential. However, most of the electrochemical techniques are only able to qualitatively describe the kinetics of the redox process. Among various electrochemical techniques employed for redox active compounds, characterization cyclic voltammetry (CV) is the most prevailing method for quick and sufficient electrochemical characterization of various soluble species1,2,3. The CV technique has broad applications, e.g., energy levels estimations4,5,6, the charge carriers analysis supported by spectroscopies7,8,9,10, up to surface modifications11,12,13. Like every method, CV is not perfect and to increase the applicability and quality of results, the connection with another spectroscopic technique is important. We already present several investigations where the electrochemical impedance spectroscopy (EIS) technique was employed14,15,16 but in this work, we intended to show step-by-step how to reinforce the CV technique by EIS.
The EIS output signal consists of two parameters: real and imaginary parts of impedance as functions of frequency17,18,19,20. It allows estimation of several parameters responsible for charge transfer through the electrode-solution interface: double layer capacitance, solution resistance, charge transfer resistance, diffusion impedance and other parameters depending on system investigated. Charge transfer resistance was an object of high attention since this parameter is directly related to the redox rate constant. Even though oxidation and reduction rate constants are estimated in solution, they may generally characterize the ability of a compound for charge exchange. EIS is considered to be an advanced electrochemical technique requiring profound mathematical understanding. Its main principles are described in modern electrochemistry literature17,18,19,20,21,22,23.

<table border="0" cellpadding="0" cellspacing="0" style="width:655px;" width="655">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Potentiostat</td>
			<td style="width:133px;">BioLogic</td>
			<td style="width:152px;">SP-150</td>
			<td style="width:171px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Platinum disc electrode</td>
			<td style="width:133px;">eDAQ</td>
			<td style="width:152px;">ET075</td>
			<td>1 mm diameter</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Platinum wire</td>
			<td style="width:133px;">&#8722;</td>
			<td style="width:152px;">&#8722;</td>
			<td>counter electrode</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Silver wire</td>
			<td style="width:133px;">&#8722;</td>
			<td style="width:152px;">&#8722;</td>
			<td>silver electrode</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Electrochemical cell</td>
			<td style="width:133px;">eDAQ</td>
			<td style="width:152px;">ET080</td>
			<td>3 mL volume</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Polishing cloth</td>
			<td style="width:133px;">eDAQ</td>
			<td style="width:152px;">ET030</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Alumina slurry</td>
			<td style="width:133px;">eDAQ</td>
			<td style="width:152px;">ET033</td>
			<td>0.05 &#181;m</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Butane torch</td>
			<td style="width:133px;">Portasol</td>
			<td style="width:152px;">Mini-Torch/Heat Gun</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:199px;">Dichloromethane (DCM)</td>
			<td style="width:133px;">Sigma-Aldrich</td>
			<td style="width:152px;">106048</td>
			<td></td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:199px;">Tetrabutylammonium tetrafluoroborate (Bu4NBF4)</td>
			<td style="width:133px;">Sigma-Aldrich</td>
			<td style="width:152px;">86896</td>
			<td></td>
		</tr>
	</tbody>
</table>

electrochemical impedance spectroscopy as a tool for electrochemical rate constant estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

The first step is cyclic voltammetry characterization presented in Figure 1. Application of EIS was successful when compounds underwent the fast reversible electrochemical process. Such behavior was often not observed for organic compounds but organic compounds that possess electroconductivity in a solid state was found to be a good specimen for electrochemical kinetic investigation. One such organic compound is shown in the inset of Figure 1.
Registration of impedance spectra was carried out according to the experimental setup (Figure 2), and typical raw resulting data are shown in Figure 3. Analysis of impedance spectra was carried out using special software24. The window of the open access program EIS Spectrum analyser24 during results processing is shown in Figure 4. An EEC used to fit the spectrum is built manually in the right upper sub-window. The calculated EEC parameters (resistances R1 and R2, capacitance C1 and diffusion impedance parameter W1) are shown in a table in the left upper sub-window. The graph in lower left sub-window illustrates fitting of experimental results (red points) with the theoretically calculated data plot (green line).
Several different EEC may fit experimental spectrum depending on the processes that take place on the electrode surface and their rates (Figure 5). The simplest semi-infinite Warburg element can be used as there is no distortion of solution (e.g. rotating of the electrode mixing) and no electrode coating limiting the diffusion. In case of considerably fast electrochemical reactions, resistance R3 (Figure 5A) was high enough to be neglected in comparison with other parallel branches of EEC (Figure 5B). Moreover, when rate of charge transfer (R2) is significantly higher than diffusion, the charge transfer step becomes limiting and an even simpler EEC (Figure 5C) describes the system.
The series resistor R1 is always present in EEC. It corresponds to the external resistance including connectors and solution, except electrode-surface interface. Capacitor C1 characterizes a double layer formed at the electrode interface. The branch including resistor and Warburg element diffusion impedance (Figure 5A) corresponds to a fast electrochemical process including two stages: kinetic and diffusion, respectively. The third resistor corresponds to a slower electrochemical process that takes place on the electrode surface and involves solvent or molecules that have undergone fast oxidation or reduction. In some cases, parameters, R3 and W1 were impossible to estimate. Then they might be considered as absent and not taken into account as Figure&#160;5B and 5C show.
Although EIS provides an estimation of several parameters, the target element which is considered in this work is charge transfer resistor R2 usually assigned as Rct in literature17,18,19, which stands in parallel to the capacitor and in series to Warburg element. Its dependence on voltage is shown in Figure 6.
According to the theory of electrochemical kinetics (Protocol, step 5.2), charge transfer resistance is directly related to the standard electrochemical rate constant. Even though matching between experimental and theoretical results was not ideal, it allowed estimation of the value of the standard electrochemical rate constant and defined the value of equilibrium potential by maximum position.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56611/56611fig1.jpg" /> 
Figure 1: Cyclic voltammogram of investigated compound overlapped by cyclic voltammogram in presence of small amount of ferrocene. Solution: 1.0 mol&#8729;L&#8722;1 Bu4NBF4 and 0.01 mol&#8729;L&#8722;1 X in dichloromethane. Structure of compound X (2,8-bis(3,7-dibutyl-10H-phenoxazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide) is shown in the inset. <a href="https://cloudflare.jove.com/files/ftp_upload/56611/56611fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56611/56611fig2.jpg" /> 
Figure 2: Experimental setup controlling registration of 20 spectra within the voltage range from 0.6 to 0.8 V in the frequency range from 10 kHz to 100 Hz with 20 points for each decade. Ei, Ef- initial and final potentials respectively, N - number of steps, ts- waiting time before each measurement, dt - record time interval, fi, ff- initial and final frequency, ND- number of frequency points in one spectrum, Va- ac amplitude, pw - part of time in respect to one point registration used to switch to another frequency, Na- number of measurements at one frequency, E range, I range, Bandwidth - technical parameters. <a href="https://cloudflare.jove.com/files/ftp_upload/56611/56611fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56611/56611fig3.jpg" /> 
Figure 3: Scan of screen during impedance spectra registration. Upper right sub-window: staircase dependence of electrode potential on time. Upper left sub-window: Nyquist plot, imaginary impedance (ordinate), real impedance (abciss). Lower left sub-window: Bode plot, impedance module (left scale), phase shift (right scale), frequency (horizontal scale). <a href="https://cloudflare.jove.com/files/ftp_upload/56611/56611fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56611/56611fig4v2.jpg" /> 
Figure 4: &#171;EIS Spectrum analyzer&#187; program window during results processing. Upper left sub-window: parameter values table: C1 - capacitance, R1, R2 - resistances, W1 - Warburg element; lower left sub-window: experimental (green points) and theoretical model (red line) spectra; upper right sub-window: equivalent electrical circuit; lower right sub-window: calculated statistics of fitting. <a href="https://cloudflare.jove.com/files/ftp_upload/56611/56611fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56611/56611fig5.jpg" /> 
Figure 5: Equivalent electrical circuits found to fit the impedance spectra of redox processes on the electrode surface. (A) - reversible electrochemical process accompanied by parallel irreversible process, (B) - reversible electrochemical process, (C) - electrochemical process with kinetic limitation stage. <a href="https://cloudflare.jove.com/files/ftp_upload/56611/56611fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56611/56611fig6v2.jpg" /> 
Figure 6: Inverse values of charge transfer resistance estimated from EIS versus electrode potential. The line depicts theoretically predicted dependence according to formula (2).

Watch this Scientific Journal Video about Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation at JoVE.com

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

electrochemical-impedance-spectroscopy-as-tool-for-electrochemical

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JoVE Journal

Chemistry

24.6K Views.  Silesian University of Technology. Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Video: Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid and deployment of renewable energy technologies. Among the many flow battery chemistries, non-aqueous flow batteries have the potential to achieve high energy density because of the broad voltage windows of non-aqueous electrolytes. However, significant technical hurdles exist currently limiting non-aqueous flow batteries to demonstrate their full potential, such as low redox concentrations, low operating currents, under-explored battery status monitoring, etc. In an attempt to address these limitations, we recently reported a non-aqueous flow battery based on a highly soluble, redox-active organic nitronyl nitroxide radical compound, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). This redox material exhibits an ambipolar electrochemical property, and therefore can serve as both anolyte and catholyte redox materials to form a symmetric flow battery chemistry. Moreover, we demonstrated that Fourier transform infrared (FTIR) spectroscopy could measure the PTIO concentrations during the PTIO flow battery cycling and offer reasonably accurate detection of the battery state of charge (SOC), as cross-validated by electron spin resonance (ESR) measurements. Herein we present a video protocol for the electrochemical evaluation and SOC diagnosis of the PTIO symmetric flow battery. With a detailed description, we experimentally demonstrated the route to achieve such purposes. This protocol aims to spark more interests and insights on the safety and reliability in the field of non-aqueous redox flow batteries.

We present the protocols for electrochemically evaluating a symmetric non-aqueous organic redox flow battery and for diagnosing its state of charge using FTIR.

Redox flow batteries have been considered as one of the most promising stationary energy storage solutions for improving the reliability of the power grid ...

NMR Spectroscopy as a Robust Tool for the Rapid Evaluation of the Lipid Profile of Fish Oil Supplements

The western diet is poor in n-3 fatty acids, therefore the consumption of fish oil supplements is recommended to increase the intake of these essential nutrients. The objective of this work is to demonstrate the qualitative and quantitative analysis of encapsulated fish oil supplements using high-resolution 1H and 13C NMR spectroscopy utilizing two different NMR instruments; a 500 MHz and an 850 MHz instrument. Both proton (1H) and carbon (13C) NMR spectra can be used for the quantitative determination of the major constituents of fish oil supplements. Quantification of the lipids in fish oil supplements is achieved through integration of the appropriate NMR signals in the relevant 1D spectra. Results obtained by 1H and 13C NMR are in good agreement with each other, despite the difference in resolution and sensitivity between the two nuclei and the two instruments. 1H NMR offers a more rapid analysis compared to 13C NMR, as the spectrum can be recorded in less than 1 min, in contrast to 13C NMR analysis, which lasts from 10 min to one hour. The 13C NMR spectrum, however, is much more informative. It can provide quantitative data for a greater number of individual fatty acids and can be used for determining the positional distribution of fatty acids on the glycerol backbone. Both nuclei can provide quantitative information in just one experiment without the need of purification or separation steps. The strength of the magnetic field mostly affects the 1H NMR spectra due to its lower resolution with respect to 13C NMR, however, even lower cost NMR instruments can be efficiently applied as a standard method by the food industry and quality control laboratories.

Here, high-resolution 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy was used as a rapid and reliable tool for quantitative and qualitative analysis of encapsulated fish oil supplements.

The western diet is poor in n-3 fatty acids, therefore the consumption of fish oil supplements is recommended to increase the intake of these essential ...

Phthalic Acid Ester-Binding DNA Aptamer Selection, Characterization, and Application to an Electrochemical Aptasensor

Phthalic acid esters (PAEs) areone of the major groups of persistent organic pollutants. The group-specific detection of PAEs is highly desired due to the rapid growing of congeners. DNA aptamers have been increasingly applied as recognition elements on biosensor platforms, but selecting aptamers toward highly hydrophobic small molecule targets, such as PAEs, is rarely reported. This work describes a bead-based method designed to select group-specific DNA aptamers to PAEs. The amino group functionalized dibutyl phthalate (DBP-NH2) as the anchor target was synthesized and immobilized on the epoxy-activated agarose beads, allowing the display of the phthalic ester group at the surface of the immobilization matrix, and therefore the selection of the group-specific binders. We determined the dissociation constants of the aptamer candidates by quantitative polymerization chain reaction coupled with magnetic separation. The relative affinities and selectivity of the aptamers to other PAEs were determined by the competitive assays, where the aptamer candidates were pre-bounded to the DBP-NH2 attached magnetic beads and released to the supernatant upon incubation with the tested PAEs or other potential interfering substances. The competitive assay was applied because it provided a facile affinity comparison among PAEs that had no functional groups for surface immobilization. Finally, we demonstrated the fabrication of an electrochemical aptasensor and used it for ultrasensitive and selective detection of bis(2-ethylhexyl) phthalate. This protocol provides insights for the aptamer discovery of other hydrophobic small molecules.

A protocol for the in vitro selection and characterization of group-specific phthalic acid ester- binding DNA aptamers is presented. The application of the selected aptamer in an electrochemical aptasensor is also included.

Phthalic acid esters (PAEs) areone of the major groups of persistent organic pollutants. The group-specific detection of PAEs is highly desired due to the ...

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 ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

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 ...

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is &#34;blind&#34; with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites.
The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

The use of FTIR spectroscopy for investigation of the surface properties of polycrystalline solids is described. Preparation of sample pellets, activation procedures, characterization with probe molecules and model studies of CO2 adsorption are discussed.

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids ...

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (TH, ~40-90 &#176;C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a TH = 70 &#176;C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We ...