An electrochemical preferential oxidation (ECPrOx) process, an alternative to the conventional preferential oxidation (PrOx), is developed to cleanse CO from a hydrogen-rich gas mixture using a device similar in structure to the proton exchange membrane fuel cell. In this process, the selective CO electro-oxidation is achieved at the anode by rendering the process electrochemical and by utilizing autonomous anode potential oscillations when operated at a constant low current density. The oscillation period and amplitude of the ECPrOx device adjust automatically to the CO levels in the feed stream so that a self-controlled autonomous potential pulsing is achieved with a low level of CO in the cleansed reformate. Some supplemental electrical power is produced from the ECPrOx device while CO is removed from the reformate gas, without any H-2 or CO being wasted. The ECPrOx device can be operated at near room temperature, high anode pressure, atmospheric air pressure, and without external humidification. However, the operating conditions or the structure of ECPrOx are not optimized in this paper, but rather the feasibility of the concept is evaluated with a single cell unit. © 2005 The Electrochemical Society. [DOI: 10.1149/ 1.1905983] All rights reserved.