Half-cell and noise voltages at a metal-electrode and dilute solution interface

The detection of bioelectric signals is usually based on an electrode-skin contact that is often mediated by a layer of conductive gel. This interface produces a DC voltage (half-cell potential) and a random noise voltage whose relationship is not well known. The first may cause amplifier saturation and the second posits a limit to the detection of small signals. This work investigates the mechanisms of generation of these two voltages in the simpler case of a metal-electrolyte junction and finds a theoretical expression for both, under a few simplifying hypotheses. An expression is found that relates the two voltages to the ionic concentration and to the parameters defining the dynamics of the adsorption–desorption phenomena taking place at the interface. A relationship is found between the two voltages that is in qualitative agreement with experimental findings reported in the literature. This theoretical background provides a basis for further investigation of the metal-gel and of the gel-skin interfaces not addressed in this work.