Pyrolytic carbon deposition on porous cathode tubes and its use as an interlayer for solid oxide fuel cell zirconia electrolyte fabrication

A high-quality fugitive pyrolytic carbon (PyC) film is used as an interlayer material in fabricating solid oxide fuel cells (SOFCs) by electrophoretic deposition (EPD). The carbon must both be highly conducting and burn away cleanly; hence, a graphitic or pyrolytic carbon is required. In this investigation, optimum conditions for PyC deposition from propylene pyrolysis (i.e., CVD) were ascertained. Propylene was decomposed at temperatures of 725, 775, and 825 degrees C and at 1 atm pressure with different residence times (10-20s) onto a porous LaMnO3 tube surface. Depending on the temperature and residence time, two different ranges of carbon deposit reactivities were obtained, corresponding to disordered and ordered carbon states, respectively. Temperature-programmed oxidation, scanning electron microscopy, and micro-Raman spectroscopy analyses indicate that the creation of uniform and sufficiently thick films with the highest degree of atomic ordering occurs at temperatures between 725 and 775 degrees C and a gas residence of about 14 s. Notably, the same carbon deposition conditions produced crack-free and gastight YSZ films (15-20 mm) during the fabrication of SOFCs by EPD and subsequent sintering. (C) 2001 The Electrochemical Society.