Catalyst layers coating RDE

For catalyst layer-coated RDE, there are two major steps one is to prepare the catalyst ink, and the other is to coat the catalyst... 

To study the ORR kinetics catalyzed hy the catalyst or catalyst layer-coated electrode, the RDE current—potential curves are normally recorded at different electrode rotating rates when the electrolyte solution is saturated with O2 or air. In order to obtain the steady-state curves, the controlled potential scan rate is normally slow such as less than 10 mV s In order to maintain the O2 concentration inside the electrolyte solution, O2 or air huhhling is maintained over the electrolyte solution during the data collection. The current—potential curves such as those shown in Figure 5.5(A) can be obtained and used to obtain the information about the ORR kinetics, as we discussed previously. In Figure 5.5, the catalyst is the Pt-based catalyst. Here, we present another example for non-noble metal catalyst to show how can the Koutecky—Levick theory be used in evaluate the ORR parameters catalyzed by non-noble metal catalyst. 

RDE is a commonly used technique for investigating the ORR in terms of both the electron transfer process on electrode surface and diffusion—convection kinetics near the electrode. To make appropriate usage in the ORR study, fundamental understanding of both the electron transfer process on electrode surface and diffusion—convection kinetics near the electrode is necessary. In this chapter, two kinds of RDE are presented, one is the smooth electrode surface, and the other is the catalyst layer-coated electrode. Based on the electrochemical reaction 0 + ne R), the RDE theory, particularly those of the diffusion—convection kinetics, and its coupling with the electron-transfer process are presented. The famous Koutecky—Levich equation and its... 

Schmidt et al. [23] used a conventional electrochemical half-cell to characterize the electrocatalytic properties of highly dispersed electrocatalysts in an RDE configuration. The WE was rotating GC coated by Pt/Vulcan catalyst powder that had been impregnated with a thin Nation ionomer film. RDE measurements on the catalyzed HOR showed that if the equivalent Nafion film in the catalyst layer was too thick, the mass transfer process could be significantly affected. To take account of this effect, an alternative expression to Eqn (12.2) was written as follows ... 

Unlike the RDE technique, which is quite popular for characterizing catalyst activities, the gas diffusion electrode (GDE) technique is not commonly used by fuel cell researchers in an electrochemical half-cell configuration. The fabrication of a house-made GDE is similar to the preparation of a membrane electrode assembly (MEA). In this fabrication, Nation membrane disks are first hot-washed successively in nitric acid, sulphuric acid, hydrogen peroxide, and ultra-pure water. The membranes are then coated with a very thin active layer and hot-pressed onto the gas diffusion layer (GDL) to obtain a Nation membrane assembly. The GDL (e.g., Toray paper) is very thin and porous, and thus the associated diffusion limitation is small enough to be ignored, which makes it possible to study the specific kinetic behaviour of the active layer [6],... 

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