Porosity Control of LSM/YSZ Cathode Coating Deposited by Electrospraying A. Princivalle, D. Perednis, R. Neagu, and E. Djurado* Laboratoire d’Electrochimie et de Physico-chimie des Mate ´ riaux et des Interfaces, ENSEEG-INP Grenoble, Domaine UniVersitaire, BP 75, 1130 rue de la Piscine, 38402 St Martin d’He ` res Cedex, France ReceiVed September 3, 2004. ReVised Manuscript ReceiVed December 23, 2004 The deposition of a composite electrode, which consisted of a mixture of a solid electrolyte (YSZ) and an electrocatalytic material (LSM), on an YSZ substrate was studied using the electrostatic spray deposition (ESD) technique. Films with various morphologies were obtained. The surface morphology was strongly influenced by the deposition temperature, precursor solution flow rate, and nozzle to substrate distance as a function of the nature of precursor solution. Processes involved in the porous film formation were discussed. Powder X-ray diffraction analysis showed that only the LSM hexagonal phase and the cubic YSZ phase were formed in the LSM/YSZ composite cathode after thermal treatment at 800 °C. Introduction Main issues in solid oxide fuel cells (SOFCs) development are recently focused on cost reduction and improvement of durability in long-term operation. In this context, SOFCs will be operated at reduced temperature from the traditional 1000 to 800 °C. Consequently, detrimental chemical reactions between the electrode materials and electrolyte will be avoided. A decrease in the operating temperature can be achieved by improving the electrode performance, that is, reducing the electrode overpotentials especially at the cathode. In general, two research directions are suggested in the literature: (i) optimizing the microstructure of the electrochemically active layers, 1 and (ii) a replacement of pure electronic conductor cathode by mixed ionic electronic conductor (MIEC). 2,3 Composite cathodes consisting of a mixture of strontium- doped lanthanum manganite (LSM) and the electrolyte materials such as yttria-stabilized zirconia (YSZ) or gado- linia-doped ceria (GDC) are regarded as promising cathodes for the intermediate temperature solid oxide fuel cells. Steele et al. 4 concluded that composite electrodes not only provide very effective electronic and ionic pathways to electrode/ electrolyte interfaces, but also enhance the injection of mobile charged oxygen surface species into the YSZ electrolyte. Addition of YSZ to the LSM cathode improved the adhesion of the electrode onto the YSZ substrate and significantly enlarged the triple phase boundary (TPB) area, where the gas, the electrode, and the electrolyte are in contact. 3 The enlargement of the TPB area has led to a pronounced improvement in electrochemical performance of the LSM/ YSZ composite cathode. Also, the composite cathodes consisting of the GDC and the LSM have better electro- chemical performance than the cathode consisting of LSM alone. 5 Perry Murray et al. 6 have compared the electrochemi- cal performance of the pure LSM and composite LSM/GDC cathode. The results have shown that the addition of GDC to LSM yielded 7 times lower interfacial resistance as compared to LSM. Hayashi et al. 7 also have observed low cathodic overpotential in the case of adding YSZ to LSM. Jorgensen et al. 8 have reported that composite LSM/YSZ cathodes under 0 dc polarization showed little or no degradation. The chemical reaction between the LSM and the YSZ can cause a degradation of the composite cathode. A-deficient perovskites or B-site hyperstoichiometric perovskites seem to be favorable candidates due to their decreased tendency to form insulating zirconates such as La 2 Zr 2 O 7 , SrZrO 3 at the YSZ/LSM interfaces. Therefore, in this work, we have selected the (La 0.85 Sr 0.15 ) 0.95 MnO 3-δ composition as previ- ously reported. 9 The composite cathodes consisting of 40% YSZ and 60% LSM were chosen, because the addition to the cathode of up to 40% YSZ improved its performance as has been shown by Østergård et al. 2 and Deseure et al. 10 The electrostatic spray deposition (ESD) technique pro- vides the potential to produce a large variety of ceramic thin films. In the ESD technique, a precursor solution is atomized into charged droplets by an electrohydrodynamic force. As * Corresponding author. Tel.: +33-4-7682-6684. Fax: +33-4-7682-6777. E-mail: elisabeth.djurado@lepmi.inpg.fr. (1) Holtappels, P.; Bagger, C. J. Eur. Ceram. Soc. 2002, 22, 41. (2) Østergård, M. J. L.; Clausen, C.; Bagger, C.; Mogensen, M. Electro- chim. Acta 1995, 40, 1971. (3) Wang, S.; Jiang, Y.; Zhang, Y.; Yan, J.; Li, W. Solid State Ionics 1998, 113-115, 291. (4) Steele, B. C. H.; Hori, K. M.; Uchino, S. Solid State Ionics 2000, 135, 445. (5) Xia, C.; Zhang, Y.; Liu, M. Electrochem. Solid-State Lett. 2003, 6, A290. (6) Perry, M. E.; Barnett, S. A. Solid State Ionics 2001, 143, 265. (7) Hayashi, K.; Yamamoto, O.; Nishigaki, Y.; Minoura, H. Solid State Ionics 1997, 98, 49. (8) Jørgensen, M. J.; Holtappels, P.; Appel, C. C. J. Appl. Electrochem. 2000, 30, 411. (9) Roux, C.; Djurado, E.; Kleitz, M. Proceedings of the International Energy Agency Joint Topical Meeting, Solid Oxide Fuel Cells under real operating conditionssMaterials and Processes; Les Diablerets: Switzerland, 28-31 January, 1997. (10) Deseure, J.; Dessemond, L.; Bultel, Y.; Siebert, E. J. Eur. Ceram. Soc., to be published. 1220 Chem. Mater. 2005, 17, 1220-1227 10.1021/cm048503h CCC: $30.25 © 2005 American Chemical Society Published on Web 02/08/2005