The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst

The electrochemical promotion of the C2H4+O-2 reaction to form CO2 and H2O is studied in the 10(-5) and 10(-4) mbar range with a Pt catalyst interfaced as working electrode to yttrium-stabilized zirconia (YSZ). Photoemission electron microscopy (PEEM) was used as spatially resolving method. Under open-circuit conditions, that is, without an external voltage applied, the CO2 production exhibits a pronounced hysteresis upon cyclic variation of p(C2H4). The hysteresis is attributed to the build-up of a carbonaceous CHx layer inhibiting O-2 adsorption and hence poisoning the reaction. It is shown that the application of a positive potential of 1 V triggers a transition from the unreactive branch of the reaction to an active branch. The large non-Faradayicity reported in the literature for this reaction system is explained as an ignition effect caused by the partial removal of the inhibiting carbonaceaous layer.