![]() Electrochemical reversibility refers to the electron transfer kinetics between the electrode and the analyte. Analytes that react in homogeneous chemical processes upon reduction (such as ligand loss or degradation) are not chemically reversible (see discussion below on EC Coupled Reactions). (3) Chemical reversibility is used to denote whether the analyte is stable upon reduction and can subsequently be reoxidized. If the reduction process is chemically and electrochemically reversible, the difference between the anodic and cathodic peak potentials, called peak-to-peak separation (Δ E p), is 57 mV at 25 ☌ (2.22 RT/ F), and the width at half max on the forward scan of the peak is 59 mV. The two peaks are separated due to the diffusion of the analyte to and from the electrode. This corresponds to the halfway potential between the two observed peaks ( C and F) and provides a straightforward way to estimate the E 0′ for a reversible electron transfer, as noted above. At points B and E, the concentrations of Fc + and Fc at the electrode surface are equal, following the Nernst equation, E = E 1/2. The Fc present at the electrode surface is oxidized back to Fc + as the applied potential becomes more positive. While the concentration of Fc + at the electrode surface was depleted, the concentration of Fc at the electrode surface increased, satisfying the Nernst equation. When the switching potential ( D) is reached, the scan direction is reversed, and the potential is scanned in the positive (anodic) direction. Thus, upon scanning to more negative potentials, the rate of diffusion of Fc + from the bulk solution to the electrode surface becomes slower, resulting in a decrease in the current as the scan continues ( C → D). ![]() This slows down mass transport of Fc + to the electrode. The volume of solution at the surface of the electrode containing the reduced Fc, called the diffusion layer, continues to grow throughout the scan. At point C, where the peak cathodic current ( i p,c) is observed, the current is dictated by the delivery of additional Fc + via diffusion from the bulk solution. It indicates that during the experiment the potential was varied linearly at the speed (scan rate) of 100 mV per second.Īs the potential is scanned negatively (cathodically) from point A to point D ( Figure 3), is steadily depleted near the electrode as it is reduced to Fc. A crucial parameter can be found in the caption of Figure 2: “υ = 100 mV/s”. The arrow indicates the beginning and sweep direction of the first segment (or “forward scan”), and the caption indicates the conditions of the experiment. Each trace contains an arrow indicating the direction in which the potential was scanned to record the data. However, the potential axis gives a clue to the convention used, as explained in Box 1. Two conventions are commonly used to report CV data, but seldom is a statement provided that describes the sign convention used for acquiring and plotting the data. The current axis is sometimes not labeled (instead a scale bar is inset to the graph). The x-axis represents a parameter that is imposed on the system, here the applied potential ( E), while the y-axis is the response, here the resulting current ( i) passed. ![]() The traces in Figure 2 are called voltammograms or cyclic voltammograms. The practical experiments in this text are the basis for the instruction of new researchers in our laboratory. ![]() Practical experiments and examples centered on nonaqueous solvents are provided to help kick-start cyclic voltammetry experiments for inorganic chemists interested in utilizing electrochemical methods for their research. Here, we update, build on, and streamline seminal papers (8-11) to provide a single introductory text that reflects the current best practices for learning and utilizing cyclic voltammetry. While several textbooks and online resources are available, (1-5) as well as an increasing number of laboratories geared toward undergraduate students, (6, 7) no concise and approachable guide to cyclic voltammetry for inorganic chemists is available. As the field evolves rapidly, the need for a new generation of trained electrochemists is mounting. Molecular electrochemistry has become a central tool of research efforts aimed at developing renewable energy technologies. Electron transfer processes are at the center of the reactivity of inorganic complexes. ![]()
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