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Alan Slater, St. Marys ON
KISS !!! Keep It Simple & Safe. That is #1 for me and it also stands for microchemistry.
A simple, safe fuel cell
Reprinted from page 34, October 1999
Looking ahead to the new millenium I thought that this idea was
most appropriate. As well, it illustrates the result of the sharing
of ideas that Reg Friesen encouraged us all to do through this
magazine and various conferences.
I made fuel cells some 25 years ago but used 2 M NaOH which
is quite corrosive and eats away at corks. At Chem Ed 97
Lynne Hogue (Miami University, Ohio) showed the simple
electrolysis of water with 2 pencils, using a saturated solution of
Epsom salts (MgSO4•7H2O). In earlier issues of Chem 13
News I have mentioned uses of Epsom salts! Why didn’t I see
this one?!!
Epsom salts solution – Place Epsom salts in one well to about
1/3 full and fill with water. Use a thin stem pipet to mix and
dissolve the Epsom salts. Draw up most of the solution into the
pipet leaving the well about 1/4 full of solution. Place the thin
stem into an inverted electrode tube and slowly dispense the
solution into the narrow tube. Remove the thin stem as the tube
fills. Make sure that the solution beads up on the end then
invert the electrodes and place them into the 24-well plate. It is
very important NOT to get an air bubble at this end or you will
not have a complete circuit. Fill the other electrode tube the
same way.
To ensure there is a complete circuit you can test with a
multimeter across the two electrodes.
I always had problems with leaks also. Microchemistry solved
that problem, for which I am indebted to Brother Carmen’s idea
of electrolysis using two narrow tubes in a 24-well reaction plate
(see the diagram). Finally, a good seal can be made simply and
quickly using a hot glue gun. Thus a newer, simpler, safer
electrolysis-of-water apparatus was born. BUT, more
importantly a fuel cell was also made. The fuel cell reactions
are:
9-V battery
C-electrode
glue plug
Red’n
½ O2 + 2 H+ + 2 e– → H2O
Eo = + 1.23 V
Oxid’n
H2 + 2 OH– → 2 H2O + 2 e–
Eo = + 0.83 V
Overall
H2 + ½ O2 → H2O
ΔEo = + 2.06 V
plastic tube
24 well plate
MgSO4(aq)
Equipment
Carbon electrodes – A drafting pencil lead from a stationery
store can be snapped in two to make two carbon electrodes.
Electrode tubes – I use 2- or 5-mL disposable serological pipets
that can be cut into at least four smaller sections. This gives
you a scale to measure gas volumes. If the measuring aspect is
not important use a Bic pen barrel (clear plastic) and cut it into 2
pieces.
Glue plug – Place the carbon electrode in the tube as in the
diagram. Squeeze some hot glue around the carbon electrode
and immediately immerse this end vertically into cold water.
This will set the glue AND test for any leaks.
24-Well reaction plate – This is the ‘beaker’ for the electrolysis/
fuel cell solution. If you use a comboplate well it is too small for
two tubes cut from a 5 mL serological pipet (Bic pen barrels are
fine). You could even use a bottle cap for this.
Cell operation
Attach a 9-V battery clip and alligators to the two electrodes,
then attach the 9-V battery. In a few seconds gas bubbles
should be seen at each electrode as hydrogen and oxygen are
produced. Some of these gases will absorb into the carbon
electrodes thus creating the necessary criteria for a fuel cell.
To set up the fuel cell all you need to do is disconnect the
battery and battery clips, set a multimeter to the 2-V scale and
attach it across the two electrodes. A voltage of about 1.7 V
should be found.
Questions to consider could be: How long will this cell last?
Does this time depend on how long the electrolysis ran? What
effect would a larger/smaller diameter electrode have? ∎
September 2008/CHEM 13 NEWS 15