Hydrogen Production on an Ethanol Dehydrogenation Reactor Coupled to a Conventional PEMFC

On board hydrogen storage has become a key factor for the technical viability of fuel cell driven electric vehicles. As the volumetric energy density of hydrogen is very low, on board storage of hydrogen remains a challenge in terms of weight, volume, kinetics, safety, and cost. Hydrogen can be produced from the steam reforming of ethanol (SRE) in a single-reactor usually operated in the temperature range of 823–1073 K so to avoid coke formation and to obtain high hydrogen yield. However, above 823 K the reverse water-gas shift reaction becomes thermodynamically favored to form carbon monoxide due to the high selectivity for the formation of C–C bond cleavage products (methane and CO), against the steps of C–O bond cleavage product (ethylene). Such formation of CO should be avoided because the PEMFC (proton exchange membrane fuel cell) conventional anode can only tolerate less than 10 ppm of CO, when operating in a low-temperature range (353–393 K). On the other hand, copper-based catalysts have been successfully employed for the selective conversion of ethanol to ethyl acetate or acetaldehyde. The best results for selective conversion to ethyl acetate has been achieved with ZrO₂-supported copper catalysts, even though it provides 2 electrons/ethanol molecule against 12 electrons from ethanol dehydrogenation. However CO-free hydrogen gas phase and liquid fine chemicals can be produced at temperatures as low as 523 K. In this work we present results of a system which comprises an ethanol dehydrogenation catalytic unit coupled to a conventional PEMFC. Ethanol is first dehydrogenated over a Cu/ZrO₂ catalyst bed, and then the gas effluent is trapped in a simple cold condenser enabling a gas current rich in H₂ to feed a PEMFC with Pt/C electrodes. Chromatography showed that the liquid effluent is formed essentially by ethyl acetate which has heat of combustion between ethanol and gasoline. Thus, in a hybrid propulsion system for vehicles, the electricity generated by the fuel cell may feed an electric motor, while ethyl acetate may be used as fuel of an internal combustion engine. Chronoamperometry (at a cell potential of 0.7 V) showed apparent stability of the cell performance at about 300 mA cm^-2 (with H₂ produced from ethanol dehydrogenation) whilst at 550 mA cm^-2 with pure H₂ (from a cylinder). Cyclic voltammetry of the anode and cathode after four hours of reaction showed ease recovery to the fuel cell start conditions. The unprecedented and challenging development combines on line hydrogen production with a liquid renewable feedstock (ethanol) which employs low cost copper-based catalyst. Based on electrochemical experiments, the integrated system proved to be feasible, and so may play an important role to the progress of hybrid ethanol-hydrogen fuel cell vehicles.