THE ELECTROCHEMICAL POTENTIAL REVISITED

The electrochemical potential of a charged species involves a certain ambiguity when defined following the convention used in physics and thermodynamics, where the reference point for electrical potentials is taken at infinity. A thermodynamic model system is used to elucidate the source of the ambiguity and its consequences. As a result it is shown that by choosing a point inside one of the phases of the system as a reference point, the ambiguity entirely disappears. This proposed convention is implicitly used when defining the zero point of the redox potential scale by means of the standard hydrogen electrode. It is also implicitly used to describe bioelectrochemical and bioenergetic phenomena, a usage which is here shown to have a rigorous foundation. A further aspect of this investigation is the finding that the electrostatic energy of a system and thus the electrical contribution to the electrochemical potential of a species is entropic in character.