Hydrodynamic Voltammetry Measurement with RDE and RRDE

1. Introduction

As the electrode reaction for the chemical species in solution occurs on the interface of solution (liquid phase) and electrode (solid phase), in general it proceeds through three elementary steps:
1) substrate mass transfer to the electrode surface;
2) electron transfer reaction on the electrode surface;
3) product diffusion from the electrode.
Electrode reaction rate (current) is considered to be controlled by the slowest process. It is very important to understand the electrode performance controlling process. For example, if the activity of the fuel cell catalyst itself is high enough (the electron transfer reaction is fast), the cell performance can be greatly improved by designing a highly efficient mass transfer electrode (GDE).
Utilizing the rotating disk electrode (RDE) system can control the mass transfer rate for 1) and 3) processes, so that the electrode activity 2) can be quantitatively analyzed in sufficient reproducibility 1-2).
By combining a ring electrode with a disk electrode, the rotating ring disk electrode (RRDE) measurement can help to detect RDE reaction products, their intermediates etc., so that the detailed reaction mechanism can be analyzed3).
In this technical note, while the detailed theoretical formula and analyzing method was omitted, the experiment for RDE & RRDE, such as apparatus using for RDE & RRDE measurement and the basic experimental methods were mainly described. Moreover, the method acquiring the limiting diffusion current data, and Levich and Kouteck-Levich plots preparation method were introduced in brief.

2. RRDE-3A Rotating Ring Disk Electrode Apparatus

The feature of hydrodynamic voltammetry (RDE, RRDE) is carrying out electrochemical measurement while working electrode is rotating. In order to obtain the mass transfer rate in good reproducibility, it is very important to keep the electrode rotating in a stable speed during the measurement. Hereby, we would like to introduce our new product electrode rotator RRDE-3A Rotating Ring Disk Electrode Apparatus. If RRDE-3A Rotating Ring Disk Electrode Apparatus is equipped with a rotating disk electrode (RDE) (shown in the Figure 1 upper left), the disk working electrode can rotate during electrochemical measurement.
A rotating ring disk electrode (RRDE) is shown in lower left of Figure 1. The disk electrode is in the center position, and a thin insulating layer and a ring electrode locate around the disk electrode in the shape of a concentric circle. When the RRDE electrode is set up to the RRDE-3A Rotating Ring Disk Electrode Apparatus, the rotating ring disk electrode measurement can be carried out easily. If you have the RRDE-3A Rotating Ring Disk Electrode Apparatus, you can do both RDE and RRDE measurements easily.

The simple specifications for RRDE-3A Rotating Ring Disk Electrode Apparatus are described as follows:

1. Rotation range: 100 ∼ 8000 rpm
2. Rotation accuracy: < 0.1%
3. Power supply: 1100 - 240 VAC; 50/60 Hz
4. Operating temperature: 10 - 50°C
5. Inlet gas pressure: 5 psi maximum
6. Size (W x D x H): 190 × 230 × 380 mm
7. Weight: 6 kg

Besides the normal rotation function, the motor portion can be upside down so that the spin coating can be easily done if an acrylic pipe is used together. This function is quite convenience for the electrode modification with catalyst.
Moreover, the cell supporting plate is available for cell moving up and down freely, and not only the ALS cells but also other cells can be used. Furthermore, gas purge function is equipped in RRDE-3A Rotating Ring Disk Electrode Apparatus, the manual purge time control is available certainly, it works with ALS electrochemical analyzer, and the remote purge time control is also possible.

Electric contact between rotating electrode and potentiostat is performed through the carbon brushes contacting to the rotation shaft. Figure 3(a) shows the shaft attached with electrode. The electrode can be removed easily by twisting with fingers. You can see the shaft without electrode in Figure 3(b), and the disk and ring tip parts are insulated by PEEK. The disk tip contacts with the disk electrode, so the disk current goes through the shaft center and flows to the top of the shaft, as shown in Figure 3(c). The ring tip contacts with the ring electrode and the ring current flows to the middle of the shaft. By using two pairs of the carbon brush contacting to the upper and middle parts of the shaft (Figure 4), the ring and disk currents can flow to the potentiostat during electrodes rotating. If the carbon brushes are worn, the noise will occur during measurement. If you find serious noise, please check the carbon brush firstly. If wearing of the carbon brushes is too serious, please replace them.

References

1) A.J. Bard and L. R. Faulkner. Electrochemical Methods Fundamentals and Applications 2nd Edition, Wiley, New York (2001).
2) K. Oyaizu, M. Yuasa, et al. Electrochemistry, 73, 1060 (2005).
3) K. Oyaizu, M. Yuasa, et al. Electrochemistry., 74, 81 (2006).

Technical note

      Hydrodynamic Voltammetry Measurement Using
Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE)
      - Introduction
      - Rotating disk electrode (RDE) measurements
      - Rotating ring disk electrode (RRDE) measurement