Conductance by Direct and Alternating Currents

Hermann Lndwig Ferdinand von Helmholtz (1821-1894) was a German scientist who made significant contributions to a number of areas in chemistry and physics. In physics, he contributed to the development of the conservation of energy theory and made fnndamental input to the formulation of chemical thermodynamics. He is well known for a formulation of the electric donble layer and concepts of the electrode/electrolyte interface. 

Inzelt, and F. Scholz, Electrochemical Dictionary, Springer, Berlin, Germany, 2008. 

FIGURE 3.11 Interface between a negatively charged electrode and an electrolyte solution. 

FIGURE 3.12 Magnitude of the current, I, in an electrolytic cell as a function of the applied ac and dc potential, E. E-q is the magnitude of the decomposition potential. 

Let us assume that an electric conductor has both the ionic and electron conductivity. Then an ac test will allow us to measure the conductor resistance due to both the ions and electrons. However, with a dc test, only electron conductance can be measured, if a potential below the decomposition potential is applied. The separation between the ionic and electron conductance can also be carried out using a sophisticated electrochemical technique, which is called electrochemical impedance spectroscopy (EIS). 

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