Kinetics and mechanism of the electrochemical oxidation of graphite in bisulphate melts

Abstract

The kinetics of the electrochemical oxidation of graphite to volatile compounds by electrolysing molten bisulphates in the temperature range from 180 to 320°C has been studied by conventional steady-state and non-steady-state measurements. CO₂, CO and traces of SO₂ are formed during the electrochemical reaction. Assuming 4 Faraday/mol of CO₂, the anodic efficiency is about 90%. The CO₂/CO ratio is about 2 and is independent of the cd in the range considered. The electrochemical reaction is compared to the thermal oxidation of graphite. The reaction is interpreted through a scheme involving consecutive reactions, where the rate-determining step, under Temkin conditions, is a thermal process involving a desorption of intermediates following either a first-order or second-order process depending on the type of adsorption obeyed. The activation energy derived from the rate constant at the rest potential is about 42·5 Kcal/mol.