Changes in the iron(III)/iron(II) redox process at a gold microelectrode in liquid and frozen low temperature perchloric and sulfuric acid electrolyte media

Voltammetric studies of the Fe³⁺ + e^- ⇌ Fe²⁺ electrode process have been undertaken at a 2.5 μm radius gold disk microelectrode in liquid and frozen perchloric and sulfuric acid electrolyte. Studies when the electrolyte contains Fe³⁺, Fe²⁺ or mixtures of Fe³⁺and Fe³⁺ reveal that the redox mechanism changes from diffusion control in the liquid state at ambient temperatures to a surface confined pathway in frozen media at low temperatures with the reversible potential for both electron transfer pathways being essentially the same. In perchloric acid electrolyte, over the temperature range 0 to -60°C, where ice is present, both mass transport pathways are observed simultaneously. The rate of electron transfer in the low temperature studies in acidic electrolyte is considerably enhanced by the presence of sulfate ions, as is the case in the liquid state at ambient temperatures.