Page 13 - Fuel Cell Student Edition

can be replenished. This diminishes performance In the electrolyte, zinc hydroxide that was
of the cell. If we look up the reduction potential for produced at the anode forms zinc oxide, water, and
this reaction in a standard reduction potential hydroxide.
table [9], we find that this half reaction has a
potential of +0.68V under standard conditions (100
kPa and 25˚C).
The overall cell reaction is:
At the anode, zinc is oxidized to form zinc
hydroxide and free electrons. This is an oxidation
reaction because the zinc loses 2 electrons.
Modeling of theoretical current (amperes) is beyond
the scope of this lab. In this case, it is much simpler
and more accurate to build the fuel cells than try
The reduction potential for this half reaction is -0.76V. to obtain an accurate model from incomplete
By subtracting the cathode and anode potentials, we information.
get the theoretical standard cell potential.
Once the cell has been depleted, it will need to be
CATHODE POTENTIAL – ANODE POTENTIAL = recharged. Zinc-Air fuel cells are electrochemically
STANDARD CELL POTENTIAL recharged and mechanically recycled. [11] The
process is to chemically dissolve zinc hydroxide
0.68V -0.76V = 1.44V that forms on the zinc anode, then repack with
recycled zinc beads, and recycled electrolyte.
In practice, we will never see this potential in any There are some zinc and electrolyte losses in this
cell because of losses due to changing electrolyte process.
conditions when the cell is producing electricity.
The pH and temperature of the cell will also affect The recharging procedure is beyond the scope of
the output. this lab but provided for informational purposes.

12 TOTAL REDOX™ – FUEL CELLS TOTAL REDOX™ – FUEL CELLS 13