In the early 1800's a British scientist discovered the fuel cell effect. He immersed
two platinum electrodes in sulfuric acid electrolyte and supplied hydrogen at one
electrode and oxygen at the other. The resulting reaction created a current flow
between the electrodes. There was no practical application of fuel cells at that time
because of high cost and technological problems. In the 1960s, researchers at the
University of Vienna demonstrated a fuel cell that was specific for alcohol. This
evolved into the present-day cell used in all fuel cell-based breath alcohol
measurement instruments.
In its simplest form, the alcohol fuel cell consists of a porous, chemically inert
layer coated on both sides with finely divided platinum oxide (called platinum black).
The manufacturer impregnates the porous layer with an acidic electrolyte solution, and
applies platinum wire electrical connections to the platinum black surfaces. The
manufacturer mounts the entire assembly in a case, which also includes a gas inlet
that allows a breath sample to be introduced. Various manufacturers employ numerous
proprietary nuances in their construction. The basic configuration, however, follows
that described above and illustrated above.
The chemical reaction that takes place in an alcohol fuel cell converts alcohol to
acetic acid. In the process, this conversion produces a fixed number free electrons
per molecule of alcohol. This reaction takes place on the upper surface of the fuel
cell. H+ ions are freed in the process, and migrate to the lower surface of the cell,
where they combine with atmospheric oxygen to form water, consuming one electron per
H+ ion in the process. Thus, the upper surface has an excess of electrons, and the
lower surface has a corresponding deficiency of electrons. If you connect the two
surfaces electrically, a current flows through this external circuit to neutralize
the charge. This current is a direct indication of the amount of alcohol consumed by
the fuel cell. By measuring the amount of current, you can determine the amount of
alcohol in the sample.
The alcohol fuel cells used in Intoximeters, Inc. instruments are highly specific for
alcohol on the human breath. The fuel cell produces a linear relationship between
current created and alcohol concentration in the breath sample.
Early methods of analyzing the fuel cell output measured the peak rate
of reaction and were limited in their ability to deal
with the reduced rate of the alcohol oxidation when a series of positive samples were
provided in succession.
Current patented methods used for analyzing the output of the cell have
solved this problem in that they measure the amount of current generated
from the alcohol oxidization reaction as opposed to the rate at which
the current was generated. By using this method, the same fuel cell produces results that do not significantly
degrade with use and remain within calibration for extended periods of time.
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