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.