Electrodes characterization

1 Preparation of the Working Electrodes for Catalyst/Catalyst Layer Studies In fuel cell catalyst/catalyst layer down-selection, the process of preparing the working electrodes includes several steps  

Selection of the working electrode substrates, such as glassy carbon or pyrolytic graphite. These substrates have insignificant catalytic activity towards fuel cell reactions (e.g., ORR, hydrogen oxidation reaction [HOR], and methanol oxidation), so they will not interfere with the catalytic activity of the targeted catalyst. 

Pre-treatment of the electrode substrate, which involves polishing, sonicating, and rinsing. The electrode can be pohshed using diamond pastes or alumina, followed by ultrasonic cleaning in water, acetone, or ethanol, and is then rinsed to obtain a clean surface. 

Formation of a thin catalyst layer on the clean electrode surface through surface attachment, such as dropping catalyst ink onto the electrode surface. For either a monolayer or a multilayer of the catalyst on the electrode surface, the bare electrode can be inserted into the soaking solution containing the catalyst, and then taken out and rinsed with water. 

Installation of the catalyzed electrode into the electrochemical cell for measurement. This process is suitable for stationary electrode measurement, rotating disk electrode (RDE), and/or rotating ring-disk electrode (RRDE). 

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Subsequently one plots InNo vs tHe and extrapolates to tHe=0. This plot provides the 02 desorption kinetics at the chosen temperature T. The intersect with the N0 axis gives the desired catalyst surface area NG (Fig. 4.8) from which AG can also be computed. More precisely NG is the maximum reactive oxygen uptake of the catalyst-electrode but this value is sufficient for catalyst-electrode characterization. 

Since the specific surface area of modem graphite materials is Sv 104 -r- lO m 1 (Sm 10-2 - 104m2g 1 ), it is almost always possible to make an electrode characterized by A > 1 from a mixture of a carbon material and a solid reagent. 

J.H. Yun, V.C. Yang, and M.E. Meyerhoff, Protamine-sensitive polymer membrane electrode characterization and bioanalytical applications. Anal. Biochem. 224, 212-220 (1995). 

In a real experiment one uses at least four electrodes (see Fig. 12.2), one counter and one reference electrode on each side, and measures the difference in potential between the two reference electrodes. In principle each reference electrode could be referred to the vacuum scale using the same procedure that was outlined in Chapter 2. However, in practice the required data are not available with sufficient accuracy. Of course, the voltage between the two reference electrodes characterizes the potential difference between the two phases uniquely. It can be converted to an (estimated) scale of inner potential differences by using the energies of transfer of the ions involved. 

Rotating electrodes characterize the BASF cell of Figure 19.19(b), which is used for making adiponitrile. The cell described in the literature has 100 pairs of electrodes 40 cm dia spaced 0.2 mm apart. The rapid flow rate eliminates the need for diaphragms by sweeping out the oxygen as it is formed. 

Film electrodes have been essential components of quartz microbalance studies of stoichiometry of many electrodeposition and dissolution experiments as well as polymer electrode characterization [25]. In the quartz microbalance, changes in mass are detected by measurement of changes in the resonant frequency of a quartz crystal oscillator as the mass adhering to the surface changes. The oscillation is feasible because thin-film metal electrodes (typically gold) applied to opposing faces of a piezoelectric quartz crystal serve both to induce the oscillation and to provide a site for electrochemical reaction. 

Electrode Characterization. To minimize the number of adjustable parameters of the model, the optical and electronic properties of the CdSe crystal electrode were meaured. Diffuse... 

Table I. CdSe Single Crystal Electrode Characterization...

Section 2.2.1 above introduced the concept of homogenous electron transfer in a generic donor acceptor supermolecule A-L-B. Here, the most commonly applied theoretical treatments of heterogeneous electron transfer are discussed. In this scenario, A is now an electrode characterized by continuous or semi-continuous... 

The electrochemical properties of the Ni(lll) electrode characterized in UHV were studied using Cyclic Voltammetry, a fairly common, but powerful technique for electrochemical studies °2. In a voltammetry experiment the current I through the working electrode was recorded while its potential was cycled in a sawtooth pattern. The experimental I/V curve is called a voltammogram. Features in a voltammogram due to charge transfer provide useful information of electrochemical reaction... 

VS. SCE, measured by the ratio of the SERRS band intensities at 1370 cm Fe(III) and 1360 cm Fe(II) agrees with the average of the anodic and cathodic potentials (—0.72 V and —0.58 V), see Fig. 30, 31. Furthermore, the irreversible character of the cyclic voltammetric redox process at a silver electrode, characterized by a potential peak separation larger than 0.06 V can also be illustrated by the non-Nem-stian behaviour of the ratio of the RR band intensities. This behaviour may reflect differential rates of adsorption and desorption of the oxidized and reduced species. 

This method is very useful when multiple samples are arranged in a library array, with the test cell moving from one sample to another to perform PEC electrode characterizations, or when epoxy encasement is undesirable. To confine the electrolyte over the semiconductor area of interest, an O-ring is used to seal the contact between the electrode and test cell that contains the electrolyte. The O-ring should... 

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