Electrolyte - Diode" - an Experimental Study. Polarization Phenomena at the Junction of the Aqueous Solutions of an Acid and a Base Part II (original) (raw)

Transient Response of the Acid-base Diode for Polarity Change

Periodica Polytechnica Chemical Engineering, 2021

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 ...

Negative salt effect in an acid-base diode: Simulations and experiments

The Journal of Chemical Physics, 2010

The paper describes a new phenomenon discovered in the electrolytic analog of a semiconductor diode. As an example, the phenomenon is studied in the 0.1M KOH–0.1M HCl diode where the alkaline and the acidic reservoirs are connected by a hydrogel cylinder. First the traditional, so-called positive salt effect is discussed. In that case some salt is added to the alkaline reservoir of a reverse biased electrolyte diode and as a result, close to a critical concentration of the added salt the electric current increases sharply. The so-called negative salt effect appears as a suppression of the positive one. It is shown by numerical simulations, by approximate analytical formulae, and also by experiments that the high current caused by the salt contamination in the alkaline reservoir can be mostly suppressed by relatively small salt concentrations in the acidic reservoir. Thus a straightforward application of the negative salt effect would be the sensitive detection of nonhydrogen cations...

Numerical modeling of salt effects in weak acid – weak base diodes

Journal of Electroanalytical Chemistry, 2018

This work studies the effect of salt contamination in weak acid-base diodes by numerical modeling. In a positive salt effect some salt is added to the alkaline reservoir, while the negative salt effect appears as a suppression of the positive one by contaminating also the acidic side of the diode. First, the positive and negative salt effects were investigated for weak electrolytes and they were found to be similar to those in a traditional strong acidbase diode. Next, positive and negative salt effects were studied when the ions of the contaminating salt were different from that of the weak electrolytes. In the positive salt effect it was found that at a certain critical concentration of the added salt the current increases sharply in a nonlinear fashion. In a negative salt effect it was found that the diode current responds strongly even for small changes in the salt concentration on the acidic side. The sensitivity of a weak acid-base diode was found to be similar to that of a strong one, thus it can be also applied as a sensitive detector of nonhydrogen cations in an acidic medium. Furthermore, weak electrolytes provide milder conditions for the non-reactive parts of the diode, and their potential profiles can also be more suitable for ion detectors.

Analysis of the electrolyte diode. Electro-diffusion and chemical reaction within a hydrogel reactor

2000

A reaction-diffusion system describing the electrolyte diode is investigated. This consists of a chemically crosslinked polyvinylalcohol (PVA) hydrogel cylinder in which a pH gradient is provided by having an acid and a base maintained at constant concentrations in reservoirs at each end of the one-dimensional reactor. A potential difference of a given strength is also applied across the gel cylinder. Previous experimental studies of the current-voltage characteristics (CVC) have shown two distinct cases, depending on whether a positive or negative potential difference was applied. The slopes of the linear current-voltage response curve are substantially different in the two cases, that in the 'forward' case being typically several orders of magnitude greater than that in the 'backward' case. Thus the system behaves like a semiconductor diode. The stationary concentration distribution for the different ions is described by a system of reaction-diffusion equations involving migration caused by the electric field. An approximate solution of these equations, using a simplified model, is presented and compared with results obtained by solving the full system numerically. The concentration profiles obtained from the numerical solution confirm the validity of the simplified model.

The origin of the electrode effect in various electrolytes

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1978

The problem of the origin of electrode effects in various electrolytes is studied on the ground of Fourier's equation. Thus the electrolysis time elapsed before the occurrence of an electrode effect is shown to be equal to the calculated time which is the time necessary to bring the temperature of the electrolyte surrounding the electrode up to its boiling point. Then we can conclude in all cases investigated that the electrode effects are induced by a Joule effect heating of the electrolyte.

Chemical Diode

The Journal of Physical Chemistry, 1996

A chemical active medium on the base of Belousov-Zhabotinsky (BZ) medium was used to design a "chemical diode". This system, similar to a semiconductor diode, shows unidirectional propagation of chemical pulses and may be possible to be used to construct a massively parallel computational medium. The system of two mesoporous glass plates with ferroin loaded at the surface was covered by BZ solution and maintained propagating excitation waves. The unidirectional propagation was observed when the plates were placed so that the corner of the one plate was close to the plane side of the other plate. The study shows that the important feature of the system is the geometrical arrangement of the plates and the gap distance between them. Computer simulations confirm the experimental results.

EXPERIMENT 5: MOLAR CONDUCTIVITIES OF AQUEOUS ELECTROLYTES

Objective: To determine the conductivity of various acid and the dissociation constant, a K for acetic acid 1 Theory 1.1 Electrical conductivity in solutions An electric current in solution is the result of the net movement of free ions in a specific direction. The current may be determined by measuring the resistance R between two similar inert electrodes immersed in the solution, as in the figure below where the oval region represents the solution; A represents the electrode area and l is the normal distance between the electrode planes. In actual practice an A.C. current with a low frequency of the order of approximately 1000 Hertz is used (to prevent electrolysis) in the measurement, and the components representing the resistance R in the complex impedance Z for the circuit is determined. We will always refer to this component (the real portion of the complex impedance) for what follows. The resistance is also dependent on the frequency (Debye-Falkenhagen effect). The theory and measurement here concentrates on low frequency measurements where the Onsager equation is meaningful. The fully automated measuring apparatus has been configured for low frequency measurement in accordance with the theory of electrolytes.

CHAPTER 4 Diodes

IN THIS CHAPTER YOU WILL LEARN 1. The characteristics of the ideal diode and how to analyze and design circuits containing multiple ideal diodes together with resistors and dc sources to realize useful and interesting nonlinear functions.