Method for studying high temperature aqueous electrochemical systems: Methanol and glycerol oxidation

Abstract

A method for high purity aqueous electrochemical experiments at temperatures above the normal boiling point of water and at temperatures up to 140 °C is described. A three-electrode cell in a self-pressurized glass autoclave is heated in an oil bath. Slow ramping of the temperature allows efficient acquisition of kinetic parameters such as activation energies, oxidation onset potentials and Tafel slopes by using cyclic voltammetry. The oxidation of two organic alcohols with different volatilities, methanol (high volatility) and glycerol (low volatility), are studied to demonstrate the capabilities of the method. Methanol oxidation on platinum is found to have a similar mechanism at all temperatures, with either dissociative adsorption of water or dissociative adsorption of methanol as the rate-determining step. In the case of glycerol oxidation on platinum, the mechanism changes at 110 °C. At low temperatures dissociative adsorption of water or dissociative adsorption of glycerol is suggested to be the rate-determining step. At higher temperatures, a significant decrease in onset potential was observed and the glycerol is suggested to selectively oxidize to glyceraldehyde or dihydroxyacetone, with dissociative glycerol adsorption as the rate-determining step.