Atomic layer deposition of LSM cathodes for solid oxide fuel cells

For solid oxide fuel cells (SOFCs) to succeed as a next-generation, clean energy conversion device, they must be made to run more efficiently at low temperatures <500 degrees C. To improve electrode kinetics at these lower temperatures, we investigate using atomic layer deposition (ALD) to fabricate mixed electronic-ionic conducting electrodes of (LaxSr1-x)MnO3 (LSM). Lanthanum oxide was grown from La(Me4Cp)(3) and water with a source temperature of 220 degrees C with a stoichiometry of La2O3. Strontium oxide was grown from Sr(n-PrMe4Cp)(2) and water with a precursor sublimation temperature of 210 degrees C and a stoichiometry of SrO, with little carbon contamination. Manganese oxide was grown from Mn(Me4Cp)(2) at a source temperature of 180 degrees C and water as oxidant; the stoichiometry was confirmed to be MnO2. LSM was grown at a growth rate of similar to 3.5 nm/cycle, where one cycle was composed of the following sequence: La/H2O/La/H2O/Mn/H2O/Sr/H2O/Mn/H2O/La/H2O/La/H2O. LSM was crystalline as deposited when grown on crystalline yttria-stabilized zirconia (YSZ) substrates. On fuel cells with LSM as the 95 nm thick, dense cathode, 100 nm thick, dense YSZ as electrolyte, and porous 80 nm thick Pt anode, a peak power density of 0.2 mu W/cm(2) was achieved at 450 degrees C. Electrochemical impedance spectroscopy shows that low oxygen diffusivity in LSM and slow kinetics of the oxygen reduction reaction on LSM were the limiting resistances in the fuel cell, suggesting that LSM is not an optimal low temperature cathode. (C) 2008 Elsevier B.V. All rights reserved.