Single membrane electrode assembly

Figure 3.1. Schematic representation of a PEM fuel cell single membrane electrode assembly (MEA) with electrochemical reactions occurring at catalyst particles (dark circles).

Figure 3.3. Typical polarization curve for a H2/O2 PEM fuel cell single membrane electrode assembly with individual electrical efficiency losses (according to Figure 3 in ref. [14] reproduced with permission of JOhnson Matthey PLC).

Table 3.8. Long-Term Experiments for Catalysts in Fuel Cell Single Membrane Electrode Assemblies... 

Olson TS, Chapman K, Atanassov P (2008) Non-platinum cathode catalyst layer composition for single membrane electrode assembly proton exchange membrane fuel cell. J Power Density 183 557-563... 

HBP-SA, HBP-SA-Ac, HBP-PA and HBP-PA-Ac polymers, interpenetrated electrolyte membrane HBP-SA-co-HBP-Ac, and the crosslmked membranes CL-HBP-SA and CL-HBP-PA showed the VTF-type temperature dependence. These polymers and membranes are thermally stable up to 260 °C, and they had suitable thermal stability as an electrolyte in the polymer electrolyte fuel cell operating under non-humidified conditions. Fuel cell measurement using a single membrane electrode assembly cell with crosslinked membranes CL-HBP-SA and CL-HBP-PA was successfully performed under non-humidified conditions, and polarization curves were observed. The concept of the proton conduction coupled with the polymer chain motion was proposed as one possible approach toward high temperature fuel cells. 

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.

Collection of in situ XAS data using a single cell fuel cell avoids problems associated with bubble formation found in liquid electrolytes as well as questions regarding the influence of adsorption of ions from the supporting electrolyte. However, the in situ study of membrane electrode assemblies (MEAs) in a fuel cell environment using transmission... 

Membrane electrode assemblies (MEA) with AEM were prepared with a single-sided ELAT electrode (20% Pt on Vulcan XC-72 and 0.5 mg/cm2 Pt loading) on the cathode side and carbon only electrode on the anode side. The electrodes were assembled on both sides of a membrane without a press procedure and the assembly was sealed in the electrolytic cell. 

The mobile ions are the H+ which move from the anode to the cathode the water is produced at the cathode. Water is removed together with nitrogen and unreacted oxygen, if air is used as oxidant (see Fig. 6). The PEM single cell is often called membrane-electrode assembly (MEA). 

The main activities for the remaining part of this program will focus on optimization of the promising membrane-electrode assembly, scale-up to nominal 300 cm and validation in single cells followed by short stack evaluation. The program is scheduled to be completed in February 2003. 

In the present study, membrane electrode assemblies (MEAs) were prepared by heat pressing the membrane sample in its hydrated state with catalyzed Teflon impregnated porous carbon electrodes to form a single... 

Solutions of DMM, TMM and methanol were evaluated in single cells and a 5-cell stack supplied by Giner, Inc. The cells were operated at temperatures ranging from 25 °C to 90 °C and were heated at the ceil block and the anode fuel reservoir, which was equipped with a condenser to prevent evaporation but allow CO2 rejection from the system. In the present study, the membrane electrode assembly (manufactured by Giner Inc.) consisted of electrocatalytic Pt-Ru (50/50 atom %) and R fine metal powders (surface area 30-70 m /g) bonded to either side of a Nafion -117 polymer electrolyte membrane. The... 

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. 

The earliest PEMFC system models [1,2] were for single cells at steady state, assuming isothermal and isobar conditions. Performance is averaged over the cross-channel direction, and transport in gas channels is decoupled from transport through the Membrane Electrode Assembly (MEA). The power of... 

Fig. 3 Components of the polymer electrolyte fuel cell (PEFC) membrane electrode assembly (MEA) on the left, including separator plates and gasket. A schematic of a PEFC stack is shown on the right, comprising a number of single cells in series...

Fig. 16 Single fuel cell characterisation at 90-150°C of membrane electrode assemblies prepared using sPEEK-ZrP (20wt. % ZrP prepared in situ in sPEEK solution). Noncommercial electrodes, 1.2 mgcm PtRu anode, 1.2 mgcm Pt at cathode. 1 M methanol feed, 2.5 bar oxygen, 3 bar. Measurements at 90 °C, A lOO C, 110°C, 120 °C, 130 °C, A 140 °C, 150 °C. Unbroken line is current density vs. cell voltage dashed line is power density vs. cell voltage...

Nafion 117 (purchased from DuPont) was used as electrolyte membrane for the DMFC single cell, which was pretreated in mildly boiling water with 3% H2O2 for 2 hours, then boiled in 2 M H2SO4 for 2 hours. For each treatment the membrane was washed in de-ionized water several times. After these treatments it was stored in water for preparation of membrane electrode assembly (MEA). Johnson Matthey s unsupported Pt black (2mg/cm ) and Pt-Ru... 

Figure 1.2 schematically shows the major components of a PEM single cell. A single cell is a unit that contains only one membrane electrode assembly (MEA), i.e., one anode, one cathode, and one membrane placed between the anode and the cathode. 

M or components of a PEMFC single cell (1 = end plates 2 = current collectors 3 = flow-field plates 4 = gaskets 5 = gas diffusion media 6 = membrane electrode assembly). 

PEMFGs use a proton-conducting polymer membrane as electrolyte. The membrane is squeezed between two porous electrodes [catalyst layers (CLs)]. The electrodes consist of a network of carbon-supported catalyst for the electron transport (soHd matrix), partly filled with ionomer for the proton transport. This network, together with the reactants, forms a three-phase boundary where the reaction takes place. The unit of anode catalyst layer (ACL), membrane, and cathode catalyst layer (CCL) is called the membrane-electrode assembly (MEA). The MEA is sandwiched between porous, electrically conductive GDLs, typically made of carbon doth or carbon paper. The GDL provides a good lateral delivery of the reactants to the CL and removal of products towards the channel of the flow plates, which form the outer layers of a single cell. Single cells are connected in series to form a fuel-cell stack. The anode flow plate with structured channels is on one side and the cathode flow plate with structured channels is on the other side. This so-called bipolar plate... 

Usually, the starting point of model derivation is either a physical description along the channel or across the membrane electrode assembly (MEA). For HT-PEFCs, the interaction of product water and electrolyte deserves special attention. Water is produced on the cathode side of the fuel cell and will either be released to the gas phase or become adsorbed in the electrolyte. As can be derived from electrochemical impedance spectroscopy (EIS) measurements [14], water production and removal are not equally fast Water uptake of the membrane is very fast because the water production takes place inside the electrolyte, whereas the transport of water vapor to the gas channels is difiusion limited. It takes several minutes before a stationary state is reached for a single cell. The electrolyte, which consists of phosphoric add, water, and the membrane polymer, changes composition as a function of temperature and water content [15-18]. As a consequence, the proton conductivity changes as a function of current density [14, 19, 20). 

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. 

Figure 5.2 Sketch of the stack repeating element the single hnear air channel in the BP. From the top and bottom the element is heated by membrane-electrode assemblies (not shown).

MSC-MEA (Membrane Electrode Assembly) in cell test are 650. 568 and 443 mW/cm at 750, 700 and 650°C, respectively. For single cell MSC stack with 80% hydrogen, the maximum power densities are 391, 306 and 194 mW/cm at 750, 700 and 650 C, respectively, and the estimated degradation rate of --0.3%/kh is obtained after 1,100 hrs operation. For 5-cell MSC stack with reformed gas, the stack delivers 115.4 Watts at 700°C and 0.77 V of average cell voltage and shows no degradation after 110 hrs operation. 

In a single-cell configuration, there are no bipolar plates. The two plates on each side of the membrane electrode assembly may be considered as two halves of a bipolar plate. The fully functioning bipolar plates are essential for multicell configurations (as shown in the Figure 16), by electrically connecting the anode of one cell to the cathode of the adjacent cell. 

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