Figure 11. PICAXE 28X2 Fuel
Cell Mode Schematic.
Figure 10.
Parallax
BS2 Fuel
Cell Mode
Schematic.
may damage the fuel cell. Allow the
process to continue until 20 ml of
hydrogen are produced. Then,
remove the battery or other power
source from the setup. If you’re using
another fuel cell and you need to
clamp off the hydrogen from
escaping, do so now. Notice that the
level of hydrogen in its cylinder is
twice that of oxygen, which confirms
the 2-to-1 ratio in the familiar H2O
symbol.
Allow the entire amount of hydrogen
to be consumed as we want to be
able to start fresh with our next
experiment.
Determining the
Water Decomposition
Voltage
Fuel Cell Mode
Now we need to reconfigure our
microprocessor setup to remove the
battery or solar panel and replace it
with the fuel cell as the power source
(but don’t attach the fuel cell just
yet). We also want to add a 10 ohm
load resistor where the fuel cell used
to be. Again, don’t connect the
motor to the fuel cell as a load. Refer
to Figure 10 and Figure 11 for these
new schematic
hookups. Once
again with the REEL Power software
running, attach the fuel cell to the
circuit and witness a plot similar to
Figure 12. This is the transition from
Electrolysis to Fuel Cell Mode. Notice
the voltage, current, and power drops
as the fuel cell now begins to deliver
its stored energy into the 10 ohm
load.
I mentioned earlier that there
was a minimum voltage necessary
to separate hydrogen and oxygen
called the Water Decomposition
Voltage. The theoretical voltage is
1.23 volts DC; however, it’s higher in
actual practice due to impurities in
the electrolysis process. The
difference between the theoretical
decomposition voltage and the
measured voltage is called
“overpotential.”
Overpotential is a function of the
Figure 12.
Beginning
of Fuel Cell
Mode.
Figure 13.
Electrolysis
and Fuel
Cell Modes.
May 2010 51
