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

8Amp, respectively. The calculated and measured results are given in Figure 4.11(a) for
oxygen flow and Figure 4.11(b) for hydrogen flow.
Oxygen Production (ml/min)
35
30
25
20
15
10
5
0
a b
Figure 4.11. Calculated and Measured Oxygen and Hydrogen Flows
Averages of the measured gas output were within 1% range of the calculated values
although oxygen output readings fluctuated within 10% range of flow. This might be due to
that the excess water and oxygen competed each other to escape from the cell and also
oxygen gas bubbled through the upper part of the water reservoir was coming out; resulting
in difficulties in flow measurements with the soap flow meter.
The single cell operated at 500mAmp/cm 2 shows that the cell can generate
hydrogen at 67.9% to 75.2% efficiency. The reason of the change in the efficiency is due to
the temperature and non-optimized design of the current cell, though the results seem to be
promising as compared to previously constructed alkaline electrolyzer which operated in
previous studies at about 3.5V per cell in our institute (Atagündüz, 1993). However, the
major drawback of the current design proposed in this thesis is the operating temperature
limitation of the materials used to assemble the cell, such as melting of gasket. This
problem prevented the cell from being used at high efficiency levels; i.e. at high
temperatures.
2 4 6 8 10 12
Experiment Number
Calculated O 2 at 2Amp
Measured O 2 at 2Amp
Calculated O 2 at 8Amp
Measured O 2 at 8Amp
Moreover, to increase the cell efficiency, thinner proton exchange membranes can
be used instead of using N-117 which is 150µm in thickness because voltage drop on
membrane was proportional with its thickness. Though thinner membranes such as N-112
(50µm) have higher hydrogen back diffusion rates. Especially at low current densities,
Hydrogen Production (ml/min)
70
60
50
40
30
20
10
0
2 4 6 8 10 12
Experiment Number
Calculated H 2 at 2Amp
Measured H 2 at 2Amp
Calculated H 2 at 8Amp
Measured H 2 at 8Amp
55