Linear sweep voltammetry reference electrode

A twin electrode thin layer Kissinger cell was designed in which the channel volume could be varied through the use of PTFE spacers [174]. The working and counter electrodes were carbon paste (3.14 m ) and the reference electrode was Ag/AgCl. The performance of the cell was tested on 50 pL portions of chlorpromazine solutions in 0.01 M HCl, and the three cited methods were compared. Linear sweep voltammetry was found to be the simplest to apply and showed moderate sensitivity. 

Data from electrochemical impedance diagrams yield a simplified quantitative analysis for an appropriate interpretation of the linear sweep voltammetry (LSV) experiments. In fact, the Si electrode potential measured with respect to the reference electrode represents the value within the bulk of the material. The direct current flow for the electrochemical reaction has to overcome the resistance of the space charge layer, which can reach extremely high values when a depletion layer is formed. For p-type Si in the potential range for the HER onset, this excess surface resistance is over 10 f2 cm. Thus, even with a bias of —1 V, the DC... 

The invention of the dropping mercury electrode in 1922 by Heyrovsky [1] led to the development and the extensive use of polaro-graphy, which must be considered to be the first linear sweep voltammetry method. In the period from 1947 to 1959, the theory and practice of voltammetry at solid stationary electrodes were developed [2—20]. Due to the significant differences in the mode of mass transport to the two types of electrode, the response and the range of utility differ markedly. Thus, the techniques are sufficiently different that they must be treated separately. The generally accepted convention is that polaro-graphy refers to measurements at the dropping mercury electrode, while measurements at stationary electrodes are referred to as linear sweep voltammetry (LSV). 

Measurements of the open circuit potential (OCP) were performed by linear sweep voltammetry with the anode of the electrolyser set as the working electrode, and the cathode set as both counter and reference electrodes. The hydrogen reference electrode condition was created by saturating the catholyte with H2 gas at the room temperature. The measured OCP values were refered to the standard hydrogen electrode (SHE). Since the potential of the hydrogen reference electrode varied from SHE depending on the HC1 concentration used in the experiement, this correction was taken into account for all measured OCP. 

Linear sweep voltammetry is based on the potential being ramped up between the working and auxiliary electrodes as current is measured. The working electrode is usually a SMDE nowadays, in which case this technique would be called linear sweep polarography. In this set-up, the auxiliary electrode is a mercury pool electrode and may also serve as the reference electrode. The resultant current-potential recording (the polarogram) can yield much information which can be used to qualitatively identify the species and the medium in which it is determined as well as calculate concentrations. Analysis of mixtures is also possible. The detection limit is of the order of 10 M. 

Figure 7.3 Linear sweep voltammetry for ORR of Pl/Au(111) (red line) and Pt(111) (blue line) electrodes measured in oxygen-saturated 0.1 M HCIO4 at a scan rate of 10 mV s with a rotation rate of 1600 rpm. Inset diffusion-corrected Tafel plot of the Pt(111) electrode obtained with a rotation rate of 1600 rpm. (For interpretation of the references to color in this figure legend, the reader is referred to the online version of this book.) Reprinted with permission from 4.

Linear sweep voltammetry was used, with the convolution technique. A silver chloride-silver reference electrode was employed. The working electrode was a tungsten wire (I mm in diameter). The counter electrode was either a carbon rod or the graphite crucible. 

In linear sweep voltammetry (LSV), the citrrent passing dtrough the working electrode is measured, while the potential between the working electrode and the reference electrode is... 

Linear sweep voltammetry (LSV) was carried out using a two-electrode Kalousek cell in conjunction with a slowly dropping mercury electrode with m = 0.67 mg and natural drop-time ti = 11.4 s (in 1.0 M KCl at 0.0 V) at h = 25 cm as the working electrode and a saturated calomel electrode, separated by liquid junction, as the reference electrode. In sulfuric acid solutions of pH less than 0 an Hg/HgS04 reference electrode was used, as was previously described. The voltage scans were started 6 s after the previous drop was dislodged. 

Bioanalytical Systems BAS 100 and BAS lOOA Electrochemical Analyzers, a PAR 174 polarograph and a pulse generator-transient recorder combination were used for performing cyclic voltammetry, linear-sweep voltammetry, and chronocoulometry. Rotating-disc current-potential curves were recorded with a Tacussel model EDI electrode operating at rates of 100 to 2500 rpm. All measurements were made at ambient temperature (21 2 C) in a single-compartment cell employing saturated calomel (SCE) or saturated sodium chloride calomel (SSCE) reference electrodes and platinum discs as counter electrodes. 

Figure 2. Experimental setup for linear sweep and cyclic voltammetry. W, working electrode R, reference electrode C, counterelectrode.

There are several modifications of this technique. In ac polarography, which employs a dropping mercury working electrode, 4 is changed step-wise (one step per drop lifetime) and the diffusion layer is completely renewed after every drop fall. In linear sweep ac voltammetry, the working electrode is stationary, and dc is a linear function of time. However, when the sweep rate is slow, the polarographic and voltammetric responses are quite similar, and we will neglect the difference between those two modifications. For more details, one should consult Chapter 10 in reference (1) and the review articles cited therein. 

Theoretical treatments of cyclic voltammetry usually assume a cyclic linear potential sweep at the working electrode. However, the solution resistance causes a potential drop to exist across the working electrode and the reference electrode. Thus, the potential at the working electrode is really the applied potential plus the solution IR drop ... 

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