Patent EA-004168-B1 (EA)
Title: Composite electrodes for solid state electrochemical devices
Inventor: GHOSH DEBABRATA
IPC: H01M8/12
Filed: 2000-10-06
Abstract: 1. An electrode forming part of a solid state electrochemical device, said electrode bonded to a dense electrolyte layer and comprising a porous three-dimensional solid phase comprising: (a) an electrocatalytic phase comprising a plurality of electrocatalytic particles; (b) an ionic conducting phase comprising a plurality of ionic conductor particles; wherein said electrocatalytic phase and ionic conducting phase are interspersed and wherein the mean size of said electrocatalytic particles is substantially equal to or larger than the mean size of said ionic conducting particles. 2. The electrode of claim 1 wherein the solid phase of the electrode is comprised of about 1% to about 95% electrocatalytic phase by volume. 3. The electrode of claim 2 wherein the solid phase of the electrode is comprised of about 1% to about 50% electrocatalytic phase by volume. 4. The electrode of claim 3 wherein the solid phase of the electrode is comprised of about 5% electrocatalytic phase by volume. 5. The electrode of claim 3 wherein the solid phase of the electrode is comprised of about 30% electrocatalytic phase by volume. 6. The electrode of claim 3 wherein the solid phase of the electrode is comprised of about 50% electrocatalytic phase by volume. 7. The electrode of claim 1 wherein the mean size of said electrocatalytic particles is at least about twice as large as the mean size of the ionic conductor particles. 8. The electrode of claim 7 wherein the mean size of said electrocatalytic particles is at least about four times as large as the mean size of the ionic conductor particles. 9. The electrode of claim 1 wherein the electrode is a cathode and forms part of a solid oxide fuel cell comprising an electrolyte layer and an anode layer. 10. The electrode of claim 9 wherein the cathode is less than about10 mum thick. 11. The electrode of claim 10 wherein the cathode is less than about 5 mum thick. 12. The electrode of claim 11 wherein the cathode is less than about3 mum thick. 13. The electrode of claim 1 wherein said electrode has a vertical dimension and a horizontal dimension and said electrocatalytic phase provides continuous electronical conductivity in the vertical dimension but not in the horizontal dimension. 14. The electrode of claim 1 wherein said electrode further comprises a horizontally electronic conducting layer comprising an electronically conductive metal oxide. 15. The electrode of claim 14 wherein said electronically conductive metal oxide comprises lanthanum cobaltate. 16. The electrode of claim 1 wherein the electrocatalytic particles are comprised of a noble metal. 17. The electrode of claim 16 wherein the noble metal is palladium. 18. The electrode of claim 1 wherein the ion conductor particles are comprised of YSZ. 19. A solid state electrochemical device comprising a porous anode, a dense electrolyte and a cathode comprising a porous three-dimensional structure comprising linked particles of an electrocatalytic material and linked particles of an ionic conductor wherein the mean or median size of the electrocatalyst particles is larger than the mean or median size of the ion conducting particles. 20. The solid state electrochemical device of claim 19 wherein the device is a solid oxide fuel cell. 21. The fuel cell of claim 20 wherein the electrocatalytic material is a noble metal. 22. The fuel cell of claim 21 wherein the noble metal is palladium. 23. The fuel cell of claim 20 wherein the mean or median electrocatalytic particle size is at least about 2 times larger than the mean or median ion conductor particle size. 24. The fuel cell of claim 23 wherein the mean or median electrocatalytic particle size is about 4 to about 10 times larger than the mean or median ion conductor particle size. 25. The fuel cell of claim 20 wherein the ionic conductor is comprised of the same ion conducting material as the electrolyte layer. 26. The fuel cell of claim 25 wherein the electrolyte and ion conducting particles are both comprised of YSZ. 27. The fuel cell of claim 20 wherein the cathode is less than about 10 mum thick. 28. The fuel cell of claim 27 wherein the cathode is less than about 5 mum thick. 29. The fuel cell of claim 28 wherein the cathode is less than about3 mum thick. 30. The fuel cell of claim 20 further comprising a long range electronically conductive layer applied to the cathode. 31. The fuel cell of claim 30 wherein said long range electronically conductive layer is comprised of lanthanum cobaltate. 32. The fuel cell of claim 31 wherein said long range electronically conductive layer is not sintered prior to operation of the fuel cell. 33. A method of forming an electrode for use in a solid state electrochemical device having a dense electrolyte layer comprising the steps of: (c) mixing electrocatalytic particles with ion conducting particles where mean or median size of the electrocatalytic particles is substantially equal to or larger than the mean or median size of the ion conducting particles; and (d) creating a porous three-dimensional structure bonded to the dense electrolyte layer, said structure comprising linked particles of the noble metal particles and linked particles of the ionic conductor. 34. The method of claim 33 wherein the electrocatalytic particles, the ion conducting particles, a suitable organic binder and a suitable solvent are mixed in appropriate volumes to form a paste which is then screen printed onto the dense electrolyte. 35. The method of claim 33 wherein the electrocatalytic particles are comprised of a noble metal. 36. The method of claim 35 wherein the noble metal comprises palladium. 37. The method of claim 33 wherein the ion conducting particles are comprised of YSZ. 38. The method of claim 33 further comprising the steps of sintering the electrode and then applying a long range electronic conducting layer comprising a metal oxide. 39. The method of claim 38 wherein the metal oxide comprises lanthanum cobaltate. 40. The method of claim 33 wherein the volume percentage of electrocatalytic particles in the solid phase of the electrode is between about 1% and about 50%.