Genesis of the Nernst Equation

When Nernst started work alongside Arrhenius in Ostwald's Leipzig laboratory in 1887, there was uncertainty as to the location and quantification of the electromotive force (emf) of galvanic cells. Nernst's three seminal contributions of 1888 and 1889 (refs. 5-7) provided for the first time clear, atomistic explanations of, and quantitative expressions for, potential differences across: i) liquid junctions between two solutions of different concentrations of the same strong electrolyte; ii) electrode/electrolyte interfaces. Combined, these gave exact expressions for the emf of concentration cells and galvanic cells without liquid junction, in terms of the osmotic pressure p of each component in solution (proportional to concentration for very dilute solutions) and the 'dissolution pressure' P characteristic of each ion in a solid component. Nernst's early view that the separate terms of his whole-cell equations gave the absolute potential difference across each individual interface was later modified by the recognition that the condition of zero interfacial charge is not necessarily the condition of zero potential difference. His eponymous equations for whole cells in any case relate to relative not absolute differences, and remain the crucial cornerstone of equilibrium electrochemistry.