Oxygen reduction reaction electrochemical mass

Parthasarathy A, Srinivasan S, Appleby AJ, et al. 1992b. Pressure dependence of the oxygen reduction reaction at the platinum microelectrode/Nafion interface Electrode kinetics and mass transport. J Electrochem Soc 139 2856-2862. 

Table 6.1. Pt/VC mass activities at 0.9 V as a function of 0s,i (sulfur coverage) [41]. (Reproduced by permission of ECS—The Electrochemical Society, from Garsany Y, Baturina OA, Swider-Lyons KE. Impact of sulfur dioxide on the oxygen reduction reaction at IhA ulcan carbon electrocatalysts.)...

The basic function of a CL is to provide a place for electrochemical reactions. The main processes occurring in a CL include mass transport of the reactants, interfacial reactions of the reactants at the electrochemically active sites, proton transport in the electrolyte phase, and electron conduction in the electronic phase. The hydrogen oxidation reaction (HOR) takes place in the anode CL and the oxygen reduction reaction (ORR) occurs in the cathode CL. Both anodic and... 

These examples are based on both electrodes operating in the activation polarization regime, in which the logarithm of the current is proportional to the overpotential. However, there are situations - particularly at low concentrations - in which the electrochemical reaction is limited by mass transport to the electrode surface. This is referred to as concentration polarization, and is illustrated in Figure 13.2d. In this case, above a critical overpotential the current becomes constant, which appears as a vertical line in the plot. A new mixed potential is established at the intersection of this vertical line and the cathode polarization for the oxygen reduction. This potential depends on the gas concentration, and thus can be used for the chemical sensor signal. 

Table 10.3. Average crystallite size of Pt nanoparticles, electrochemically active area (EAA), peak current density, and mass activity for the methanol oxidation reaction of various Pt/MWCNT nanocomposite catalysts. The average size of Pt nanoparticles was obtained by XRD analysis [84]. (Reproduced from Journal of Power Sources, 161(2), Travitsky N, Ripenbein T, Golodnitsky D, Rosenberg Y, Burshtein L, Peled E. Pt-, PtNi-and PtCo-supported catalysts for oxygen reduction in PEM fuel cells, 782-9, 2006, with permission from Elsevier.)...

When dezincification occurs in service the brass dissolves anodically and this reaction is electrochemically balanced by the reduction of dissolved oxygen present in the water at the surface of the brass. Both the copper and zinc constituents of the brass dissolve, but the copper is not stable in solution at the potential of dezincifying brass and is rapidly reduced back to metallic copper. Once the attack becomes established, therefore, two cathodic sites exist —the first at the surface of the metal, at which dissolved oxygen is reduced, and a second situated close to the advancing front of the anodic attack where the copper ions produced during the anodic reaction are reduced to form the porous mass of copper which is characteristic of dezincification. The second cathodic reaction can only be sufficient to balance electrochemically the anodic dissolution of the copper of the brass, and without the support of the reduction of oxygen on the outer face (which balances dissolution of the zinc) the attack cannot continue. 

Regardless of the specific type of fuel cell, gaseous fuels (usually hydrogen) and oxidants (usually ambient air) are continuously fed to the anode and the cathode, respectively. The gas streams of the reactants do not mix, since they are separated by the electrolyte. The electrochemical combustion of hydrogen, and the electrochemical reduction of oxygen, takes place at the surface of the electrodes, the porosities of which provide an extensive area for these reactions to be catalysed, as well as to facilitate the mass transport of the reactants/products to/from the electrolyte from/to the gas phase. 

The objective of the mass transport lab is to explore the effect of controlled hydrodynamics on the rate at which a mass transport controlled electrochemical reaction occurs on a steel electrode in aqueous sodium chloride solution. The experimental results will be compared to those predicted from the Levich equation. The system chosen for this experiment is the cathodic reduction of oxygen at a steel electrode in neutral 0.6 M NaCl solution. The diffusion-limited cathodic current density will be calculated at various rotating disk electrode rotation rates and compared to the cathodic polarization curve generated at the same rotation rate. 

---