Today, pure H2 is rarely directly a

Today, pure H2 is rarely directly available. Hence, home fuel cells currently use H2 produced from natural gas from the gas grid. Natural gas is firstly converted by steam reforming (CH4 + H2O ↔ CO + 3H2) followed by a water gas shift (WGS) reactor (CO + H2O ↔ CO2 + H2) to decrease the concentration of CO (and to increase the output of H2). However, the WGS is limited by thermodynamic constraints, and the H2 rich gas still contains small amounts of CO at the outlet of the WGS, typically 0.5–1 vol% CO [2,3]. Unfortunately, even traces of CO deactivate the anode electro-catalyst of the PEMFC. Therefore, the CO content must not exceed 10 ppm for Pt-anodes and 100 ppm for Pt Ru-anodes [4,5]. Hence, the CO content in the operating gas has to be further reduced below these threshold values, preventing a degradation of the fuel cell catalyst. CO preferential oxidation (CO-PROX) has so far been a reliable technique as a fine purification step of the feed gas downstream the WGS unit [2,6–10]. In order to achieve the required low CO concentration permanently, a two-step system is usually needed [4]. In addition, this process requiresan additional, closely controlled, low rate O2 supply to keep the unwanted oxidation of hydrogen as low as possible [2,10].