Study of a new solid oxide fuel cell operated at intermediate temperatures (650°-700°C)

A new SOFC cell based on a silicate electrolyte with apatite structure is investigated for use at intermediate temperatures (IT). A dense pellet of lanthanum silicate (La 9 Sr 1 Si 6 O 26,5 ) exhibits at 700°C a conductivity of 9x10 -3 S/cm -1 that is very stable down to 10 -24 atm of oxygen at any temperature. A new cermet of mixed silicate electrolyte and nickel powders adheres to a dense substrate of lanthanum silicate electrolyte at a sintering temperature of 1100°C. Electrochemical characterization of symmetrical cells (cermet/dense silicate electrolyte/cermet) showed the lowest electrode resistance at 1100°C. However, microstructural characterizations showed a bad interconnect between cermet particles after reduction that could result from incomplete sintering of the silicate electrolyte particles. The association of silicate electrolyte with a cathode of nickelate (Nd 1.95 NiO 4+δ ) was also examined. Electrode resistance on a symmetrical cell (nickelate cathode/dense silicate electrolyte/nickelate cathode) was much less at 700°C than LSM cathode on a traditional YSZ electrolyte. Chemical compatibility of nickelate material with the silicate electrolyte was also checked.