Voltammetric studies on a glassy carbon electrode. Part II. Factors influencing the simple electron-transfer reactions—the K3[Fe(CN)6]-K4[Fe(CN)6] system

Abstract

Detailed cyclic voltammetric studies were carried out on the hexacyanoferrate(II)-hexacyanoferrate(III) redox system in H₂SO₄, Na₂SO₄, NaOH, NaCl, KCl, NaH₂PO₄, Na₂C₂O₄ and trisodium citrate media on a glassy carbon electrode. The effects of polishing and cleaning, chemical and electrochemical surface treatments, pH, supporting electrolyte cations and anions and time on the redox behaviour of the system were systematically evaluated. The following conclusions were drawn: (a) surface polishing or exposure to the atmosphere does not affect the reproducibility of the results; (b) anodic polarisation activates the electrode surface, as found in earlier studies, but some additional evidence indicates that this is due to oxidation of the fresh carbon surface, and this aspect is considered in detail; (c) the rate constants calculated for the oxidation of hexacyanofer-rate(II) and the reduction of hexacyanoferrate(III) using Nicholson's method differ substantially; this is attributed to different surface states of the glassy carbon at the starting potentials; and (d) anions have a substantial effect on both the rate constants and the limiting currents; chloride ions have a special activating effect. These effects are discussed on the basis of adsorption and mediated electron transfer. Other factors that influence the electron-transfer kinetics such as time effects and heat-treatment temperature are also discussed.