In this contribution a well-mixed electrochemical preferential oxidation (ECPrOx) reactor for hydrogen purification is considered and the influence of the CO concentration on the polarization curve, the conversion, the selectivity and the specific energy required is investigated. For that, a wide range of CO concentrations are studied and two different control modes are evaluated: voltage and current control. It was established that the oscillations, which arise during current control, enhance the reactor performance. They decrease the specific energy required and increase, as does the CO concentration, the selectivity and the conversion. Furthermore, it was found that the bifurcation current and potential vary nonlinearly with the CO concentration. (C) 2017 Elsevier Ltd. All rights reserved.