Figure 2. Parallax BS2
Schematic Hookup.
Figure 3. PICAXE 28X2
Schematic Hookup.
η F= H2 Volume (theoretical) / H2
Volume (experimental)
The energy content of hydrogen
is calculated by using the amount of
energy given off when hydrogen is
combusted. This is a given value of
286,000 Joules/mol of hydrogen
(exothermic; i.e., a chemical reaction
where heat is lost). This is called the
molar enthalpy of hydrogen at
standard temperature and pressure.
We also have the given value for the
amount of space H2 takes up per
mol. H2 has a molar volume of
24,000 mL/mol and an energy
content of 286,000 Joules/mol (1
Joule = 1 watt-second). Use the
following equations to calculate the
Energy Efficiency (η E).
η E = Electrical
energy in Joules of
• Electrical energy in Joules H2 = E
(average) x I (average) x time (s)
• Volume of H2 consumed in
mL/24,000 mL/mol, therefore …
• Energy content of consumed H2
(theoretical) = xxx mol H2 *
286,000J/mol (where xxx is the
number of H2 mols consumed).
Faraday Efficiency
The Faraday Efficiency is a
percentage that tells us how much of
the hydrogen gas is being used for
intended electrical energy production
and how much is lost to other
factors. It is the ratio between
the theoretically calculated
volumes of hydrogen
consumed by the load at a
certain current versus the
experimentally calculated
volume of hydrogen
consumed. The equation for
Faraday Efficiency (η F) is:
Horizon Hydrocar
For these experiments, we’re using the
Horizon Hydrocar reversible fuel cell and
storage cylinders, so make sure the car’s
motor switch is turned OFF and that the
wires going to the motor are not connected.
This phenomenon was originally
understood through Michael Faraday’s
work and expressed in his laws of
electrolysis. In effect, it describes the
efficiency with which electrons
(charge) are transferred in a system to
facilitate an electrochemical reaction.
The word “Faraday” in this term has
two interrelated aspects.
First, the historic unit for charge
is the faraday (look at any capacitor’s
charge value if you’re not sure), but it
has since been replaced by the
coulomb — a unit of electrical charge
equal to the amount of charge
transferred by a current of one ampere
in one second. Secondly, the related
Faraday’s constant correlates charge
with moles of matter and electrons.
The Horizon Hydrocar can
be purchased online from the
Nuts & Volts Webstore at
www.nutsvolts.com or call our
order desk at 800-783-4624.
Now to the
Experiments
Given this background
information, we can now proceed
with the experiments in confidence
that we know what we want to
measure and expect to see. We’ll be
using both the Parallax BS2 and
PICAXE 28X2 microcontrollers in our
test beds. Figure 2 and Figure 3
show their initial schematic hookups.
You can find the complete experiments
48
June 2010
