Thin-film rotating disk electrode

Electrocatalysts with a 1/8 of monolayer Pt loading on Ru nanoparticles have been synthesized by spontaneous deposition of Pt on a Ru surface, each of which have at least three times larger mass-specific activity for H2 oxidation than two commercial catalysts and a larger CO tolerance, as determined by thin film rotating disk electrode measurements. 

The thin-film rotating disk electrode has been used for determination of the catalytic activity. The catalyst was attached to the glassy carbon electrode by careful deposition from aqueous dispersion and no Nafion film was used to cover the deposit. This can significantly improve the tests of supported electrocatalysts. Kinetic parameters for the oxidation of H2 and H2 + CO have been determined by... 

The transition to more realistic conditions, near fuel cell environment, is achieved using a thin-film rotating disk electrode with a practical supported catalyst. It allows obtaining kinetic parameters such as the the exchange current density and Tafel slopes, avoiding the use of complex models. This is of fundamental importance, because small catalyst particles having a significant fraction of surface atoms could behave differently compared to bulk materials. 

Performance of PIml electrocatalysts has been determined using single-crystal surfaces [15], thin-film rotating disk electrode (RDE), and in fuel-cell membrane electrode assembly (MEA). Higher activities observed with rotating electrodes are ascribed to a better Pt utilization of Pt. Figure 6 displays the data on RDE and MEA prepared from Pt L/Pd/C nanoparticles 0.57 and 0.36 A/mgpt in Pt mass activities at 0.9 V were obtained from the measurements on RDE and MEA, respectively. 

The concentration of metal atoms in mercury electrodes depends on the potential (/face) and the duration (/acc) of accumulation, the bulk concentration of ions (CMe(b)) and the hydrodynamic conditions in the solution [26]. The simplest model considers the reversible electrode reaction on a thin mercury film rotating disk electrode with a fully developed diffusion layer in the solution and uniform distribution of metal atoms in the mercury film ... 

J. Murimboh, M.T. Lam, N.M. Hassan, and C.L. Chakrabarti. A study of Nafion-coated and uncoated thin mercury film-rotating disk electrodes for cadmium and lead speciation in model solutions of fulvic acid. Analytica Chimica Acta 423 115-126, 2000. 

Paulus UA, Schmidt TJ, Gasteiger HA, Behm RJ. 2001. Oxygen reduction on a high-surface area Pt/Vulcan carbon catalyst A thin-film rotating ring-disk electrode study. J Electroanal Chem 495 134-145. 

Thin catalyst layers on a GC rotating disk electrode (RDE) or a rotating ring-disk electrode (RRDE) serve for studies of ORR kinetics. In order to separate the kinetic current from the measured current j, Schmidt and co-workers [Schmidt et al., 1998b] corrected the latter for the influence of oxygen diffusion in the aqueous electrolyte and in the polymer film using the foUowing equation ... 

The rotating-disk electrode is a graphite disk about a half-inch in diameter held vertically it dips into a solution and carries a thin film of the solution to the top of the electrode, where it is sparked. The disk is rotated at about 5 to 30 rpm. 

Figure 8.4 shows the importance of the coordination mode around the metal ion for the electrochemical properties of the layer. In Fig. 8.4 the mediation of the Fe(II)/(III) oxidation is studied by using a rotating disk electrode. Initially a thin film of [Ru(bipy)2(PVP)5Cl] is used and with this coating the current potential curve I is obtained (see Fig. 8.4b). On photolysis of the coating and formation of the aquocomplex (according to Reaction 5) curve II is obtained. Rotating disk behavior very clearly shows that the redox potential of the modifying layer is of prime importance to the electrochemical properties of the modified electrode.

In practical applications, very often diffusion is not semi-infinite. Such finite-length linear diffusion is observed, for example, for internal diffusion into mercury film deposited on a planar electrode, in deposited conducting polymers, for hydrogen diffusion into thin films or membranes of Pd or other hydrogen absorbing materials, or for a rotating disk electrode where the diffusion layer corresponds to the layer thickness. There are two cases of finite-length diffusion displayed Fig. 4.11 ... 

This expression, eq. (7.106) or (7.107), takes into account the effect of fluid motion on the diffusion layer 8, which is an adherent thin film on the electrode surface. Therefore, diffusion coupled with convection contributes to the total mass transfer process to or from the electrode surface and it is known as convective diffusion in which 6 is considered immobile at the electrode surface [66]. Recall that the limiting thickness of the diffusion layer is illustrated in Figure 4.5. Also, Levich equation describes the effect of rotation rate, concentration, kinetic viscosity on the current at a rotating-disk electrode. 

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