This is the second part of our work dealing with electrolyte diodes with weak acids
and bases. In the first part an approximative analytical solution was derived for
the steady-state current-voltage characteristic (CVC) of a reverse-biased diode (a
quasi-one-dimensional gel connecting an acidic and an alkaline reservoir), applying
either strong or weak electrolytes. An approximative analytical solution is compared
here with a numerical solution free of any approximations and with CVCs measured experimentally
with both strong and weak electrolytes. It is shown that the deviations between the
numerical and analytical solutions are mostly due to assumptions made for the fixed
charge concentration profiles. The concept of optimal analytical solution is introduced
which does not use such assumptions and applies only the quasielectroneutrality and
quasiequilibrium approximations. It is proven that the slope of the CVC based on the
optimum analytical solution can be calculated without the complicated derivation of
that solution itself. The calculation of that slope is based on the fact that in the
optimum analytical solution all currents are inversely proportional to the length
if the boundary conditions are held constant and realizing that in the middle part
of the gel the only mobile counterions of the fixed ionized groups are hydrogen ions.
In the experimental part the apparatus and the preparation of the gel are described
together with the CVCs measured with strong and weak electrolytes. From these CVCs
the fixed ion concentration in the middle part of the gel can be determined. That
fixed ion concentration is 1.96 X 10(-4)M measured with weak electrolytes and 3.48
X 10(-4)M measured with strong electrolytes. The deviation indicates that the strong
base causes some hydrolysis of the gel. Finally, possible applications of weak acid-weak
base diodes are discussed. (c) 2005 American Institute of Physics.
