Membrane electrode assembly stream

FIGURE 8.4 Inlet partial pressures of O2 and H2 in the fuel cell feed streams as a function of inlet relativity humidity at 120°C and l.Oatm backpressure. Nation - 12-membrane-based membrane electrode assembly (MEA) with an active area of 4.4 cm [14]. (For color version of this figure, the reader is referred to the online version of this book.)... 

An actual breakthrough is to design both the microstructure (grain size, porosity,...) of the different system materials (support-membrane-catalyst) and the reactor architecture in order to obtain improved permeation properties and stability during the time on stream [19]. Considering all the parameters, a special consideration was given in this paper to the stack of the different materials at different length scale, from the microscopic-scale (microstructure) to the assembly of materials on the whole reactor thickness (architecture). An example of the architecture/microstructure concept was used in the Multi Electrode Assembly (MEA) approach. 

The ED stack is the unit holding together anionic and cationic membranes assembled in parallel as in a filter press between two electrode-end blocks in such a manner that the stream undergoing ion depletion (i.e., the diluate or diluting stream) is kept separated from the other solution (concentrate or concentrating stream) undergoing ion enrichment. Figure 4 shows an exploded view of it. 

The potentiometric technique for FIA monitoring has also been achieved by using ion-selective electrodes (ISEs - see subsection 2.1.1) assembled in a tubular reservoir (with the working electrode positioned at different points in the system). The use of a series of cascading ion-selective electrodes allows the simultaneous determination of various species [342]. To minimize the thickness of the static layer on the electrode surface and achieve an optimum wash-out effect preventing changes at the sensor membrane it is customary to use cascade-type cells in which a small portion of the carrier electrolyte stream is pumped tangentially to the electrode surface [343]. 

An automated system for potentiometric determination of free and total cyanide in wastewaters is by employing a homogeneous membrane tubular ion-selective electrode [38]. After the electrode is assembled, it is connected to a system composed of 3 three-way solenoid valves, sample line, carrier line, acid stream, and gas diffusion chamber. A turbo pascal computer program performs all the steps involved in data acquisition and processing. The proposed analytical procedure offers operational simplicity, since detection is performed by a cyanide ion-selective tubular electrode, and is fast and easy to assemble. 

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