The molecular capacitor was invented by Stern to explain the results of capacity measurements. Though much time has elapsed, the evidence (independent of electrochemistry) of its existence has not been provided so far. The situation is quite different for the electronic capacitor. It does exist at a metal surface. This unambiguously follows from the physical facts reliably established long ago: namely, the existence of free conduction electrons in a metal and their wave nature. Indeed, while colliding with a metal surface, free electrons must suffer total reflection (otherwise, they would permanently leave the metal, which contradicts the thermodynamic equilibrium principle). On the other hand, the theory of light reflection implies that under total reflection the incident wave penetrates into the surrounding medium where its amplitude decays exponentially. The situation must be the same with electrons, due to their wave nature. Thus, a negatively charged electron cloud (the outer plate of the capacitor) must be formed outside the metal (i.e. in the solution). At the same time, on the inner side of the interface (in the metal) there arises a layer, several angströms thick, in which the positive charge of the metal ion core is uncompensated, since the electrons of the layer have escaped into the solution. This layer forms the inner plate of the electronic capacitor. It should be stressed that at the zero-charge point the charge of each plate has the same value, but opposite sign, so that the system remains electroneutral; for other electrode potentials, the electronic capacitor excess charge is compensated by the charge of the ionic part (the excess charge may be produced by an external source, viz. a battery).
KeywordsPotential Drop Simple Metal Contact Potential Difference Electron Work Function Ionic Part
Unable to display preview. Download preview PDF.