hydrogen production from water using solar cells powered nafion ...

Figure 4.2. Pin Type Flow Field
Except the flow field design, the rest of the materials used in the second design
were the same as the first one. The cell was tested under the same conditions and it was
observed that the required potential difference decreased to 3.08V at 200mAmp/cm 2 which
is 38.4% lower than that obtained in the first design. But the voltage efficiency of the cell
was still about 48% even at this low current density. During this test, it was noticed that as
the bolts getting tighter, voltage of the cell decreased continuously. In fact, 5mm
polypropylene bolts could not be tightened more because they could be broken or lose
threads.
These tests showed the effect of compression on electrolysis cell that resulted in
using thicker bolts with big thread sizes on further trial which tolerated high compression.
6mm polypropylene bolts with big thread were used in the third experiment with all the
other materials were the same as the second design. At the same temperature and water
flow rate, the potential difference decreased to 2.77V at 200mAmp/cm 2 which was 10%
lower than that of the second design but still too high for such low current densities
according to the results in the literature which were given in chapter two. At the end of the
experiment, the cell was dismantled and similar to the X type flow field observations with
the first design, the surface of the GDL was not as flat as that in the beginning of the test.
On the surface of GDL, the points above the pins were little higher than the areas which
were not supported by the pins. Since the deep fields on the GDL cannot contact with
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