Volta potential difference experimental determination

The main effect of crystal orientation is caused by different barrier heights on different crystal faces. It is well known that Volta-potential differences are dependent on crystal orientation because the surface dipole differs for different faces. In the case of a semiconductor electrode this means that the flat band potential which can be determined experimentally depends... 

Since each outer potential may be determined as described above, the Volta potential difference may also be found experimentally. A method for measuring o Ap / is discussed later in this chapter. 

A schematic diagram illustrating the experimental determination of the Volta potential difference between two metals, a and p, is given in fig. 8.11. For this system, electrons are the species common to each phase. The experiment involves an arrangement in which there is an air gap between a and p. On the other side of P, there is a second portion of phase a which is designated ot, so that the system can be described as... 

Fig. 8.11 Experimental setup for determining the Volta potential difference between two metals a and p. The compensation potential is determined with potentiometer P by moving a with respect to P until there is zero current in galvanometer G.

The discussed calculation procedure is not based on any extrathermodynamic assumptions and therefore the inaccuracy of the result obtained is determined only by the experimental errors of measuring a work function and the Volta potential difference. Furthermore, from the solvent surface potential x determined by any estimation method we can find the ideal solvent-electron interaction energy Vq = U — ex . Unlike U , V, is not a strictly thermodynamic quantity and the inaccuracy in determining it, besides experimental errors, is caused by the inaccuracy of model assumptions made for estimating x -... 

This is not the only possibility for obtaining an estimate of the absolute SHE potential from electrochemical experiment. As shown in [7], the absolute SHE potential can also be determined from measurements of the potential of zero charge and contact potential (Volta potential difference) of the interface of an inert metal electrode, such as Hg with an electrolytic solution. Surveying the experimental data available at the time Trasatti decided that (abs) = 4.44 V is the best estimate. This value was accepted by lUPAC as their recommended value. Fawcett has recently reviewed the procedure, also taking into account experimental data from mass spectroscopy experiments." His conclusion was that only a small adjustment was necessary (from 4.44 to 4.42 V). 

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