An application of the so-called acid-base diode would be the sensitive detection of
nonhydrogen cations in an acidic medium based on salt-effects. For diode purposes
different connecting elements between the acidic and aqueous reservoirs of the diode
were developed, namely a polyvinyl alcohol (PVA) hydrogel cylinder, and a polyvinyl
butyral (PVB) membrane. During the measurement of the voltage – current characteristic
(VCC) of the diode, it was found, that in the case of PVA gel cylinder an overshoot
(a local maximum followed by a local minimum) appeared in the time vs. current curve,
while the diode was switched between modes (open or closed), that is the direction
of the applied voltage was reversed. The overshoot did not appear in PVB membrane.
The existence of overshoots was studied by numerical simulations. The time response
of the diode with different hypothetic connecting elements was investigated, when
the diode was switched between modes via changing the polarity of applied voltage.
We found that larger diffusion coefficients of hydrogen and hydroxide ions explain
the appearance of overshoots. By examining the concentration and potential profiles
a qualitative explanation of this phenomenon was given.
