Strategic implementation of pulsed oxidation for mitigation of CO poisoning in polymer electrolyte fuel cells

Abstract

Hydrogen generated by reforming various hydrocarbons contains impurities such as carbon monoxide (CO) and carbon dioxide (CO2) in varying concentrations. These impurities are known to poison the platinum and platinum alloy catalysts used in polymer electrolyte fuel cells (PEFCs) even at elevated temperatures. Amongst other approaches, pulsed oxidation for CO conversion has been proposed to enable usage of impure hydrogen fuel in PEFC applications. The present work evaluates the pulsed oxidation technique experimentally for practical implementation under high CO contamination levels. The implementation and effects of key operating parameters such as pulse width, current, and threshold potential for activation are systematically analyzed in terms of CO mitigation effectiveness. These parameters determine the extent of CO stripping and consequently the performance and energy conversion efficiency of the PEFC. Implementation of pulsing at set threshold potential rather than at fixed time intervals is shown to improve performance recovery up to 95% of the baseline performance under pure hydrogen. Technical means of utilizing the electrical energy generated during pulsing are discussed and measured, indicating a boost in the overall energy efficiency of the cell. Extended duration testing shows the feasibility of this technique to sustain CO poisoning in PEFCs at practical current densities.