Membrane Electrode model

The drawbacks of the original Orion liquid membrane electrode model were successfully overcome by simply incorporating the neat exchanger within a thin matrix of PVC (9). Besides having more favourable mechanical and physical characteristics, these novel PVC electrodes had prolonged functional lifetimes and a performance, in terms of Nernstian calibration, response times and selectivity coefficients, on a par with the original Orion 92-20 model. In fact, the mean content of calcium determined with the respective electrodes in tap water on 10 consecutive days was 31.55 and 31.57 ppm (9). 

Figure 15.2 Schematic representation of different electrochemical cell types used in studies of electrocatalytic reactions (a) proton exchange membrane single cell, comprising a membrane electrode assembly (b) electrochemical cell with a gas diffusion electrode (c) electrochemical cell with a thin-layer working electrode (d) electrochemical cell with a model nonporous electrode. CE, counter-electrode RE, reference electrode WE, working electrode.

Cost targets exist for all parts of the fuel cell for bipolar plates, from 10/kW (2004) to 3/kW in 2015 for electrocatalysts, from 40/kW (2005) to 3/kW in 2015 and for membrane electrode assemblies (MEA), from 50/kW (2005) to 5/kW in 2015 (Freedom Car, 2005 these cost targets are somewhat different from those mentioned by the IEA (2005)). Since 2004, the number of fuel-cell cars has been growing and at the time of writing they numbered approximately 1000 worldwide there are also around 100 fuel-cell buses in use worldwide in several demonstration projects. But these cars are produced as individual (hand-built) models and are extremely expensive, with production costs per vehicle currently estimated at around one million large-scale production is not expected before 2015, see Section 13.1. 

Modeling of Membrane-Electrode-Assembly Degradation in Proton-Exchange-Membrane Fuel Cells - Local H2 Starvation and Start-Stop Induced Carbon-Support Corrosion... 

A.Z. Weber, M.A. Hickner, Modeling and high-resolution-imaging studies of water-content profiles in a polymer-electrolyte-fuel-cell membrane-electrode assembly. Electrochimica. Acta. 53, 7668—7674 (2008)... 

The membrane conductivity was measured in HCl(aq) solutions of different concentrations and in 2 M HC1 + 0.2 M CuCl solution to model the catholyte and anolyte solutions in the electrolyser. All membranes were equilibrated in the same solutions for 20 hours before starting the measurements. Detailed characterisation data for a number of commercial anion exchange membranes are published elsewhere (Gong, 2009). The AHA membrane, which demonstrated the highest conductivity in HC1 (12.61 mS/cm) compared to other membranes with similar IEC and water uptake, was selected to prepare a membrane electrode assembly (MEA) and carry out electrolysis tests with this MEA. The ACM membrane with lower conductivity values was also chosen for the electrolysis tests due to its proton blocking properties and high Cl- selectivity. 

Figure 7. Partial pressure of 02 for a solution that originally contained 5mF Mn(II), 0.1F NaGH and 0.3F NaOH and was oxygenated for 20 min with Oz at 1 atm before degassing with argon. pH lowered by addition of concentrated HCIOj to a sealed cell. Partial pressures of 02 measured with a Beckman membrane electrode system (model 1008).

The membrane electrode assembly (MEA), which consists of three components (two gas diffusion electrodes with a proton exchange membrane in between), is the most important component of the PEMFC. The MEA exerts the largest influence on the performance of a fuel cell, and the properties of each of its parts in turn play significant roles in that performance. Although all the components in the MEA are important, the gas diffusion electrode attracts more attention because of its complexity and functions. In AC impedance spectra, the proton exchange membrane usually exhibits resistance characteristics the features of these spectra reflect the properties of the gas diffusion electrode. In order to better understand the behaviour of a gas diffusion electrode, we introduce the thin-film/flooded agglomerate model, which has been successfully applied by many researchers to... 

Molecular-Level Modeling of the Structure and Proton Transport within the Membrane Electrode Assembly of Hydrogen Proton Exchange Membrane Fuel Cells... 

The fuel cell is basically a two-scale system. The small and large scales are determined, respectively, by membrane-electrode assembly (MEA) thickness and by the length of the feed channel. The Q3D model is designed to investigate the interplay of small- and large-scale processes in PEFC/DMFC, so that the fully 3D model of the cell is split into a model of a cell cross section (internal model) and a model of the flow in the channel (channel model). The two models are coupled via the local current density along the channel and the overall Q3D solution is obtained by iterations. 

Eugster R, Spichiger UE, Simon W, Membrane model for neutral-camer-based membrane electrodes containing ionic sites. Anal. Chem. 1993 65, 689-695. 

Membrane structures that contain the visual receptor protein rhodopsin were formed by detergent dialysis on platinum, silicon oxide, titanium oxide, and indium—tin oxide electrodes. Electrochemical impedance spectroscopy was used to evaluate the biomembrane structures and their electrical properties. A model equivalent circuit is proposed to describe the membrane-electrode interface. The data suggest that the surface structure is a relatively complete single-membrane bilayer with a coverage of 0.97 and with long-term stability/... 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

Based on the Model 3, a 10-cell stack of microfuel cells was assembled. It was reported that an output of near 10 W was achieved, as shown in Fig. 8.23 [47]. Recently, through membrane electrode assembly (MEA) improvement, a power density 290 mW cm of the cell with an air cathode has been achieved. A 5-cell stack with effective area of 67 cm demonstrated that the power reached IlOW when the operating temperature reached 60 °C, though the stack started at room temperature without humidification. The performances of single ceU and 5-ceU stacks are shown in Fig. 8.24. 

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