MadSci Network: Chemistry

Re: Why does my potato battery increase voltage with time?

Date: Fri Dec 1 18:26:48 2000
Posted By: Myron Cagan, Staff Engineer, process development, micro devices
Area of science: Chemistry
ID: 975536951.Ch

This is out of my area but I will hazard a guess.  I don't think that
grouping or alignment of ions is the explanation.   Unless the coins were
cleaned with steel wool or a scouring pad, and well rinsed, it is likely
that the coins that the questioner started with had a layer of oxide (or
skin oil scum from handling) on them.  As the electrochemical reaction
proceeded PERHAPS the oxide/scum was diminished (I hesitate to say etched
away, maybe consumed in some reaction is a better way to express this).
This would improve the surface contact between the metal of the coins and
the electrolyte (potato starch).  This improved surface contact might lead
to an increased voltage from the potato battery. The questioner can test
this by STARTING with coins that have been cleaned, water rinsed, maybe then
wiped with rubbing alcohol, and then rinsed well  again with water, and then
placed in the potato with out delay.  If these cleaned coins display a
relatively high and CONSTANT voltage then my explanation is more likely to
be correct.

Since this is an educated guess the Mad Scientist Administrator might want
to poll someone on the network who lists electrochemistry or batteries as
their area of expertise.

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