Steam Electrolysis Using a Microtubular Solid Oxide Fuel Cell

Reversible operation of a microtubular solid oxide fuel cell (SOFC) with high electrochemical efficiency is reported. These devices can ideally produce hydrogen from electricity and steam [solid oxide electrolyser (SOE)] and then use the stored hydrogen to generate electricity and heat (SOFC), acting as a storage device for the electrical energy. A fuel-electrode-supported Ni-yttria-stabilized zirconia (YSZ)/YSZ/(La0.8Sr0.2)(0.98)MnO3 cell, 2.4 mm in diameter and 20 mu m of electrolyte thickness, was evaluated in an electrolysis mode as a function of the steam concentration supplied to the Ni/YSZ electrode. A good cell performance was obtained at temperatures as high as 950 degrees C for the electrolysis operation. At 850 degrees C, the cell withstood current densities of -1 A/cm(2) at 1.3 V with steam utilization of 16.5%. The production of hydrogen in the electrolyzer was tested by mass spectrometry. Their performance, especially in the SOE mode, is very promising for high temperature electrolysis applications. Voltage-current curves present an S-shaped nonlinear behavior in the electrolysis mode with a tendency to saturate at high current density values. The cell could sustain current densities as high as -6 A/cm(2) at 1.5 V, using 70% H2O/15% H-2/15% N-2 as a fuel with an area-specific resistance of the cell of 0.26 Omega cm(2). The origin of this effect is discussed. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3332832] All rights reserved.