A Study of Polarization Capacity and Resistance at Radio Frequencies

Abstract

Polarization capacity and resistance of electrolytic cells having Au and Pt electrodes in ${\mathrm{H}}_2$S${\mathrm{O}}_4$ solution, for frequencies of 11 × ${10}^4$ to 2 × ${10}^6$ cycles per second.—The cell was placed in a tuned circuit coupled to a generating circuit, and the polarization capacity $C$ was computed from the change of capacity required to restore resonance as indicated by means of a second loosely coupled circuit containing a detector and galvanometer. The polarization resistance $\Delta R$ was obtained by substituting for the cell a variable non-inductive resistance. Both $C$ and $\Delta R$ were found to be linear functions of $\frac{1}{\surd f}$ where $f$ is the frequency. For Au electrodes, the curves all go through the origin but for Pt the limits for infinite frequency are positive for capacity and negative for resistance and vary with the concentration. For both Au and Pt the slopes of the capacity curves increase with concentration while the slopes of the resistance curves decrease. In the case of Au, $2\pi \mathrm{fC}\Delta R=tan \psi =\mathrm{const}.\mathrm{}$ (nearly), whereas for Pt, $tan \psi$ varies. These results may be associated with the fact that the residual current is only 1/20 as much for Au as for Pt. The effect of previous polarization with ${\mathrm{H}}_2$ is a temporary increase of capacity, while ${\mathrm{O}}_2$ gives a permanent increase which cannot be removed by polarization with ${\mathrm{H}}_2$. The roughness of the surface as well as the previous history affect the values of $C$ and $R$ obtained. Qualitatively the results for $C$ and $\psi$ are in agreement with the theory of Warburg, provided some assumptions are made, but not the results for $\Delta R$. Possible reasons for the discrepancies are suggested.