The quantum mechanics of electrolysis

As quantum mechanics endows particles with entirely new properties, it enables us to deal with problems which have remained unsolved for many years. In electrolysis we have been unable to visualise the physical processes which underlie some of the most elementary phenomena. Thermodynamics gives a consistent account of them, independent of any mechanism; but when we try to unravel the actual processes their complexity is baffling. Quantum mechanics provides a new line of attack. One conception we find for our purpose particularly valuable—the idea that there always exists a finite probability of a particle making a spontaneous transition between any two states of equal energy. In the Sommerfeld theory of metals the valence electrons of the metallic atoms are all free electrons, so that we may regard the atoms of the metallic crystal as ions. Applying this to the anode of a copper voltameter, for example, we may say that when a current is passed, ions from the crystal lattice are leaving the surface of the electrode and slipping away into solution. The same is true of reversible gas electrodes. In great contrast to this are the processes at the electrodes of a cell where an acid is being decomposed by electrolysis. Here ions from the electrolyte are being neutralised by actual capture and loss of electrons, evolving neutral oxygen and hydrogen. Thus the phenomena of electrolysis fall into two classes, both of which may be treated by quantum mechanics. In the electrolysis of acids we encounter the complicated phenomena of “overpotential,” which provides an elaborate test for our theory; for this reason we shall be dealing in this paper with only these irreversible processes.