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Cyclic Voltammetry in Electroanalytical Chemistry Research Methods

2024-01-10 13:35

Cyclic Voltammetry (CV) is one of the most important research methods in electroanalytical chemistry. Its instrument is simple, easy to operate, and the spectrum analysis is intuitive, which is widely used in the research fields of electrochemistry, inorganic chemistry, organic chemistry, and biochemistry.

The voltammetry method is to measure the current of a system at a certain potential and obtain the voltammetric characteristic curve. Perform qualitative and quantitative analysis based on the volt ampere characteristic curve. If an isosceles triangle pulse voltage (triangular wave) is applied to the working electrode, the current voltage curve obtained includes two branches. If the first half of the potential is scanned towards the cathode direction, the electroactive substance is reduced on the electrode, generating a reduction wave. Then, when the second half of the potential is scanned towards the anode direction, the reduced product will oxidize again on the electrode, generating an oxidation wave. Therefore, a triangular wave scan completes a cycle of reduction and oxidation processes, so this method is called cyclic voltammetry, and its current voltage curve is called cyclic voltammetry. If the reversibility of electroactive substances is poor, the heights of the oxidation wave and the reduction wave are different, and the symmetry is also poor. The voltage scanning speed in cyclic voltammetry can range from several millivolts per second to 1 volt. Working electrodes can be suspended mercury electrodes, or solid electrodes such as platinum, glassy carbon, graphite, etc.

Principles of Inspection Methods

[Fe (CN) 6] 3-~[Fe (CN) 6] 4- is a typical reversible redox system, and the standard electrode potential of its redox pair is:

[Fe (CN) 6] 3-+e -=[Fe (CN) 6] 4- φ θ =  0.36V (vs. NHE)

The Nernst equation for electrode potential and electrode surface activity is:

φ = φ θ +  RT/Fln (COx/CRed)

At a certain scanning rate, during the forward scan from the initial potential (-0.2V) to the turning potential (+0.8V), [Fe (CN) 6] 4- in the solution is oxidized to form [Fe (CN) 6] 3-, generating an oxidation current; When the negative scan changes from the turning potential (+0.8V) to the original starting potential (-0.2V), the [Fe (CN) 6] 3- generated on the surface of the indicator electrode is reduced to [Fe (CN) 6] 4-, generating a reduction current. In order to ensure that the liquid phase mass transfer process is only controlled by diffusion, electrolysis should be carried out with the addition of electrolyte and solution at rest. The diffusion coefficient of K4 [Fe (CN) 6] in a 0.1M NaCl solution is 0.63 × 10-5cm · s-1; The electron transfer rate is high, making it a reversible system (in 1MNaCl solution, at 25 ℃, the standard reaction rate constant is 5.2) × 10-2cm · s-1). The dissolved oxygen in the solution has electrical activity and is removed by introducing inert gas.

Epc and Epa represent the cathodic peak potential and anodic peak potential, respectively. Ipc and Ipa represent the peak cathodic current and peak anodic current, respectively.

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