Rectification behaviour of some metal ion–metal interfaces and concentration cells

Abstract

The rectification behaviour of three metal ion–metal interfaces and 38 concentration cells was studied. The rectification in Al∣Al³⁺∣Al was 35% (−0.4 to +0.80 V d.c.) between 2.0–5.0 V a.c. and for Zn∣Zn²⁺ ⋮ Al³⁺∣Al cell was 20% (+0.20 to −0.30 V d.c.). Its negative d.c. potential showed some similarity to a tunnel diode. 20% rectification was obtained when each of Al, Zn, Mg half-cell was coupled with I⁻, I₂∣Pt half-cell and Al half-cell was coupled with Fe³⁺, Fe²⁺∣Pt half-cell. When the Zn half-cell was associated with Cr³⁺, Cr₂O₇ ²⁻∣Pt half-cell the rectification was 15%, whereas the rectification in all other concentration cells varied from 1 to 12%. The possibility of obtaining much higher percentage of rectification can be explored in a large number of other metal ion–metal interfaces and concentration cells which can be assembled in a similar manner using the table of standard reduction potentials. The characteristics of a concentration cell can be varied by change in concentration of metal ion, redox ratio, variation of pH, temperature, effect of different additives to the cell solution, irradiation of electrode surface etc. Consequently, it will affect the percentage of rectification which may be of some use in commercial applications.