Voltammetry of carbon dioxide .2. Voltammetry in aqueous solutions on glassy carbon

Variable sweep rate voltammetry of carbon dioxide at a glassy carbon electrode in aqueous solutions containing tetraethylammonium perchlorate gave two successive one-electron kinetically controlled waves. The apparently low peak potentials (-0.74 V vs. SCE at pH 10) were rationalised by consideration of the ionic radius of the tetraethylammonium cation relative to other cations. The rate limiting process appeared to be release of carbon dioxide molecules from aqueous bicarbonate. Equilibrium constants for this process were measured by rotating disc electrode voltammetry and found to be 0.069 at pH 9.1 and 0.076 at pH 10. The rate constant for the formation of carbon dioxide molecules was calculated from Kl(1/2) and found to be k(f) = 1.6 s(-1) at pH 10. However, these data conflicted with published data for this process from homogeneous kinetics. An adsorption model was applied to rationalise the data. The surface coverage was found to be 0.019 at pH 10, in line with published data.