Amperometric detection of dissolved methanol using microelectrodes

Abstract

We report on the development of a simple amperometric method for monitoring of dissolved methanol in 0.5 M – 5 M solutions in sulfuric acid (relevant to methanol levels in the feed of direct methanol fuel cells) using bare Pt microdisc electrodes. The high mass transport rates of electroactive species to the microdisc from the solution phase results in a shift of the dissolved oxygen reduction wave to more negative potentials so that it does not interfere with the main methanol oxidation peak at sufficiently positive potentials (+0.5 - +0.7 V vs. Ag/AgCl). For continuous monitoring of methanol a potential sequence consisting of +1.6 V for 10s (cleaning pulse) / 0 V for 120 s (equilibration pulse) / +0.6 V for 180 s (measurement pulse) is applied to the indicator electrode, resulting in current-time transients that are reproducible upon periodic application for at least 8 h. There is a square root correlation between the oxidation current at +0.6 V and methanol concentration for the dissolved methanol sensor in the 0.5–3 M range, in accordance with theoretical predictions, thus excluding electrode poisoning/current saturation up to 3 M . The detection limit was estimated as 0.19 M making this simple method applicable for rough estimates and a crude monitoring of methanol levels.