Bromomethane Contamination in the Cathode of Proton Exchange Membrane Fuel Cells

Abstract

The effects of bromomethane (BrCH3), an airborne contaminant, on the performance of a single PEMFC are compared with that of another halocarbon, chlorobenzene. Under a constant current of 1 A cm−2 and at 45 °C, 20 ppm bromomethane causes approximately 30% cell voltage loss in approximately 30 h, as opposed to much more rapid performance degradation observed with chlorobenzene. Electrochemical impedance spectroscopy, cyclic voltammetry, linear scanning voltammetry, and polarization measurements are applied to characterize the temporary electrochemical reaction effect and permanent performance effects. X-ray absorption spectroscopy is used to confirm that Br is adsorbed on the Pt electrocatalyst surface. We conclude that airborne bromomethane poisons a PEMFC in a different way from chlorobenzene because it is largely hydrolyzed to bromide, Br−, which is then excluded from the Pt catalyst by the negatively charged Nafion ionomer. The little Br− and bromomethane that adsorbs on the Pt surface can be partially removed by cycling but causes some irreversible surface area loss.

Impact of the Cathode Pt Loading on PEMFC Contamination by Several Airborne Contaminants

“…For naphthalene, the cell voltage transient was interrupted before a steady state was obtained (Figure 1f), which also led to a low-frequency artefact that could not be fitted to the equivalent circuits of Figure 3a-c. The impedance spectra agree with the prior results for acetonitrile [25][26][27][28], acetylene [36][37][38], bromomethane [28][29][30], isopropanol [31], methyl methacrylate [31], naphthalene [40], and propene [28,31,41]. Molecules 2020, 25 and structural modifications to the catalyst layer that are relatively more impactful for the lower catalyst loading.…”

“…a result, the current density was temporarily lowered and the contaminant injection was interrupted before a steady state was obtained to avoid an automatic test station shutdown. Contamination and recovery transients are qualitatively and quantitatively consistent with the prior results for acetylene [23,[36][37][38][39], bromomethane [23,[28][29][30], isopropanol [23,31], methyl methacrylate [23,31], naphthalene [23,40], and propene [23,28,31,41]. Figure 1b-g illustrates voltage transients for the other contaminants.…”

“…However, bromomethane transients were significantly slower and only a small fraction of the voltage loss was recovered ( Figure 1c). This behavior is the result of a rapid bromomethane hydrolysis within the cell, producing methanol and bromide [28][29][30]. The effective bromomethane concentration is lower than the nominal value, whereas bromide is prevented from penetrating the ionomer by Donnan exclusion [12].…”

Competitive Adsorption of Methyl Bromide and Water on Metal Catecholates: Insights from Density Functional Theory

“…Aside from its health hazards and deleterious effects on the ozone layer, MeBr has been identified as a poison for proton exchange membrane fuel cells. − Trace amounts of MeBr occur in the atmosphere due to production from natural sources, such as oceanic vegetation , and terrestrial woodlands . Since MeBr is present in the atmosphere, this could potentially impair the performance of automotive fuel cells, which rely on air as an oxidant …”