Anodic flow field patterning

Individual PEMFC cells produce about 0.7 V electromotive force (EMF). In order to obtain useful voltage, many cells are stacked together using a bipolar plate. It should be noted that the membrane electron assembly (MEA) for PEM is kept very thin, but the bipolar plates constitote almost 80% of the mass of PEMFC. The bipolar plate acts as an interconnect between the anode of one cell and the cathode of the next. Bipolar plates also distribute the fuel gas over the anode and oxygen over the cathode. These bipolar plates also contain cooling fluid and the different flow field patterns of bipolar plates used in PEMFC are shown in Fig. 1.12. Bipolar plates should have the following characteristics ... 

On one side the development is based on thin film and micro-patterning technologies. Wafer level and foil processes used to produce high density interconnect electronic modules, and wafer level packaging was adapted to micro fuel cell development to achieve the required miniaturisation and cost reduction. By using reactive ion etching, high aspect ratio capillary structures of the anode and cathode side flow fields were achieved. 

Fig. 46. Ionic pattern in two-dimensional electrophoresis cascade electrodes, 6 volts/cm, Veronal-Veronalate buffer, n = 0.022 and pH 8.6, 4 hours. The background buffer flow is fed with lithium buffer, the positive cascade electrode with a sodium buffer, and the negative cascade electrode with a potassium buffer. After the run, sodium, lithium, potassium, Veronal, and conductivity are determined over the entire field. Sodium and lithium migrate toward the cathode. Potassium does not leave the cathode. The total number of cations increases from top to bottom and there is also a para-anodic zone of salt concentration. Veronal and conductivity follow the same outline ( P7).

With the AFM tip as the cathode, nanowires of polycarbazole were also patterned by electric-field-induced cross-Unking and polymerization of carbazole units on an Au/mica or Si substrate (anode) spin-coated with insulating poly(vinylcarbazole) film [23,24]. Figure 10.9 shows a schematic of the experimental setup and Figure 10.10 shows an AFM image of the patterned CP nanostractures [24]. Similarly, electrochemical oxidation and cross-linking of carbazole and thiophene due to the flow of electrons from the conductive AFM tip to the polymer (polystyrene functionalized with carbazole and thiophene groups) precursor film on an Si substrate produced CP nanofeatures in the precursor polymer film [25]. 

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