Electrolyte transistors: Ionic reaction-diffusion systems with amplifying properties

The problem of constructing chemoelectric amplifying devices based on acid-base reactions is discussed. It is shown that the construction of a direct analogue of the semiconductor transistor (that is, when the p- and n-doped semiconductors are replaced by ion exchange membranes in the H+ and OH- forms, respectively) is technically not feasible. The new amplifying device reported here is based exclusively on mobile ions migrating in a hydrogel arrangement that contains no fixed charges. The polarization curve of an acid-base interface in this medium has a diode characteristic. When two of such "electrolyte diodes" are connected appropriately, a transistor action can be observed: the electric current flowing in one (reverse biased) diode is affected not only by the voltage applied there but also by the current flowing through the other (forward biased) diode. The common emitter current gain of an acid-base-acid transistor studied here was between 4 and 5. The active mode characteristics of this device can be explained by the appearance of an acidic tunnel across the alkaline middle section. Although the acid-base-acid transistor is a stable amplifying device, the base-acid-base transistor is unstable in its active mode and displays complex oscillations. The underlying bistable behavior was also demonstrated with this transistor when its acidic feedstream was contaminated with KCl.