Precedure developed by Derek Keefer and George Lisensky
An approximately 200 nm thick layer of Prussian
Blue, Fe(III)4[Fe(II)(CN)6]3, on conducting
glass can be used to make an electrochromic pixel. Electrochromic displays,
where an electrochemical redox reaction changes the pixel state, do not need
constant application of power. Such pixels have promise in electronic books
where high contrast and low power consumption are important.
K3[Fe(III)(CN)6] is electrochemically reduced
at a glass electrode to produce K4[Fe(II)(CN)6]
which reacts with Fe(III)Cl3 in solution to give insoluble
Prussian Blue, Fe(III)4[Fe(II)(CN)6]3,
on a conducting glass electrode.
Use the procedure for production of Electrochromic
Prussian Blue Thin Films to produce a 150-200 nm thick layer.
Identify the conducting side of the glass squares by using a multimeter
to measure resistance. The conducting side will have a resistance of 20-30
ohms.
Add two strips of tape to the conducting side of a glass square to
serve as a spacer. Assemble the two glass plates with conducting sides
together, but offset so that glass extends beyond the sandwich. Clamp
the plates together.
Clamp an aligator clip to the protruding end of each glass plate.
To do this experiment as a demonstration, place the assembly on an
overhead projector. Use capillary action to add a small amount of 1.0
M KCl solution between the plates. Alternately apply plus or minus 2.0 volts to produce a color change. (When
the counter electrode is a wire, a lower voltage can be used; this procedure
has two squares of conducting glass in the circuit and 2.0 V gives better results.)
A voltage is applied to change the pixel and then the circuit is interrupted.
The voltage is then reversed and the circuit reconnected. The whole process
is repeated to show the persistant nature of electrochromic pixels.
If only part of the glass is coated with Prussian Blue then only that
portion changes.
Use three glass squares coated on the diagonal to make a multiple
pixel display. Use capillary action to add a small amount of 1.0 M KCl
solution between the plates.
Alternately apply plus or minus 2.0 volts to individual pixels to
produce a color change.
A voltage is applied to change the pixel and then the circuit is interrupted.
The voltage is then reversed and the circuit reconnected. The whole process
is repeated to show the persistant nature of electrochromic pixels.
