Direct Ethanol Anode-Supported Solid Oxide Fuel Cell

Abstract

Long term durability was demonstrated on high-performance direct ethanol solid oxide fuel cell operating in gradual internal reforming. Anode supported single cells, fabricated at Forschungszentrum Jülich, composed of (La,Sr)MnO3 cathode, 8 mol% yttria-stabilized zirconia (YSZ) electrolyte, and YSZ-Ni anode were used for long term testing on anhydrous (direct) ethanol. Gadolinia-doped ceria (CGO), with 0.1 wt.% of Ir, catalyst was produced by the impregnation of Ir salt in commercial CGO (Praxair) and mixed with organic additives. The CGO-Ir suspension was deposited onto the surface of the YSZ-Ni anode support with an air brush. Such a catalytic layer acts both as a physical barrier to avoid direct contact of the fuel with Ni-based anode and to promote the gradual internal reforming of ethanol. The CGO-Ir catalyst was designed for the reforming of the main compounds resulting from the thermal decomposition of ethanol at high temperature and to inhibit the formation of ethylene, which is a known source of carbon deposits. After deposition the sample was heated at 850ºC in inert atmosphere to ensure good adhesion between the catalytic layer and the anode. Gold grid and paint were used as current collectors in both cathode and anode sides. The single fuel cells were mounted in the test apparatus, sealed with gold rings and alumina cement and heated to the measuring temperature (850°C) under inert atmosphere. After gas tightness was checked by flowing air on the cathode side and argon on the anode side, the anode was reduced under hydrogen. The fuel cell was kept at 0.6 V while monitoring the current drained from the cell at 850 °C. Samples were initially operated in hydrogen for a few hours and fuel was switched to dry ethanol, carried by nitrogen. It is important to mention that no oxidizing agent was added to the fuel and that water produced by the electrochemical reaction of hydrogen at the anode promoted the reforming of the ethanol in the CGO-based layer, in the so-called gradual internal reforming. In such conditions the current output was recorded and observed to not be significantly different form that under hydrogen. Moreover, the direct ethanol fuel cell was continuously operated for 650 hours without major losses due to carbon formation. The experimental results demonstrate that the water released by the electrochemical oxidation of reformate hydrogen at the electrolyte/anode active interfaces is sufficient for the reforming of the primary fuel in the catalytic layer, provided that a minimum fuel utilization is respected. After the durability tests, energy dispersive X-ray spectroscopy and scanning electron microscopy analyses of the samples revealed no carbon deposit formation in the anode. The experimental results provided compelling evidence for the viability of gradual internal reforming of ethanol in high performance solid oxide fuel cells.