Anode gas flow

Diffusion of water along the membrane results in the distinctly different ignition fronts with counter-current flow. The water made at the cathode of the fuel cell is partitioned between the membrane and the cathode gas flow channel. The water in the membrane diffuses to the anode where the water activity is lower, and then it can enter the anode gas flow channel. 

A computational model of an entire cell would require very large computing resources and excessively long simulation times. The computational domain in this chapter is therefore limited to one straight flow ehannel with the land areas. The full computational domain consists of cathode and anode gas flow channels, and the membrane electrode assembly as shown in Figure 3.1. 

Figure 3.5. Velocity profQes in the mid-plane of the cathode and anode gas flow channels for three different nominal current densities 0.3 A/cm (upper) 0.7 AJcm (middle) 1.2 A/cm (lower).

Figure 18.13 Water content volume fraction of MEA and GFCs as a function of current density at 50°C and 100% relative humidity inlet gas feeds (O) MEA (including GDLs) ( ) anode gas flow channel and ( ) cathode gas flow channel. Reproduced from [23] by permission of ECS-The Electrochemical Society.

Hickner et al. (2008) used high-resolution neutron radiography to image an operating PEMFC. The cross-sectional liquid water profile of the cell was quantified as a function of cell temperature, current density, and anode and cathode gas feed flow rates. At low current densities, liquid water tended to remain on the cathode side of the cell. Significant liquid water in the anode gas flow channel was observed when the heat and water production of the cell were moderate. At 60°C, the liquid water content in the center of the GDLs decreased compared to the electrolyte and catalyst layers. This profile is indicative of water condensation within the GDL and was explained by considering the microporous layers as a barrier to liquid water transport. 

The optoelectronic properties of the i -Si H films depend on many deposition parameters such as the pressure of the gas, flow rate, substrate temperature, power dissipation in the plasma, excitation frequency, anode—cathode distance, gas composition, and electrode configuration. Deposition conditions that are generally employed to produce device-quahty hydrogenated amorphous Si (i -SiH) are as follows gas composition = 100% SiH flow rate is high, --- dO cm pressure is low, 26—80 Pa (200—600 mtorr) deposition temperature = 250° C radio-frequency power is low, <25 mW/cm and the anode—cathode distance is 1-4 cm. 

Electron impact (El) ion sources are the simplest type. O2, Ar, or another (most often noble) gas flows through an ionization region similar to that depicted in Eig. 3.30. Electrons from an incandescent filament are accelerated to several tens of eV by means of a grid anode. A 20-100 eV electron impact on a gas atom or molecule typically effects its ionization. An extraction cathode accelerates the ions towards electrostatic focusing lenses and scanning electrodes. 

By locating the anode entirely upstream from the ionized gas volume, collection of long range beta particles is minimized in the displaced coaxial cylinder design, and the direction of gas flow minimizes diffusion and convection of electrons to the collector electrode. However, the free electrons are sufficiently mobile that modest pulse voltages (e.g., 50 V) are adequate to cause the electrons to move against the gas flow and be collected during. this time. 

Counter, Gas-flow Proportional (GPC)—P-particles are detected by ionization of the counter gas which results in an electrical impulse at an anode wire. If a sufficient amount of radiostrontium is present and the ionization efficiency is calibrated, the quantity of radiostrontium can be determined. 

When designing an MCFC power system, several requirements must be met. An MCFC system must properly condition both the fuel and oxidant gas streams. Methane must be reformed into the more reactive hydrogen and carbon monoxide. Carbon deposition, which can plug gas passages in the anode gas chamber, must be prevented. To supply the flow of carbonate ions, the air oxidant must be enriched with carbon dioxide. Both oxidant and fuel feed streams must be heated to their proper inlet temperatures. Each MCFC stack must be operated within an acceptable temperature range. Excess heat generated by the MCFC stacks must be recovered and efficiently utilized. 

Figure 5.2 schematically exhibits the structure and reactant flow of a simplified sfack designed by Bac 2 Conductive Composifes Inc. [5] that contains three unit cells. Some components, such as GDLs, are not shown in the simplified diagram. Each unif cell includes an MEA and a plafe (the anode plate, cathode plate, and coolant plate are not differentiated). Gas flow charmels or fluid fields are on fhe surface of each plafe. 

An improved electrochemical cell for in situ studies is presented in Figure 14.2. In this method a platinized Pt electrode located in the anode compartment serves as the reference electrode. This cell can be installed in a test station. Such a station can have facilities for temperature and pressure control, humidification of reactant gases (e.g., hydrogen and oxygen), gas flow rate measurement, and measurement of half- and... 

In the development of photoelectrochemical (PEC) solar cells, one of the most difficult problems is the corrosion problem. In any solvent, but particularly in solvents with water present, anodic currents flowing from the solid to the solution will usually lead to corrosion. Specifically the corrosion will take the form of anodic oxidation of the semiconductor, with the products remaining as a film, dissolving into the solution, or evolving as a gas. Any such action will degrade the solar cell. 

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