Performance of ionic-conducting ceramic/carbonate composite material as solid oxide fuel cell electrolyte and CO2 permeation membrane

Novel composite materials composed of an oxygen ionic-conducting ceramic oxide and a molten carbonate phase have recently been reported to be the promising materials for the electrolyte of intermedaite temperature (500–700 °C) solid oxide fuel cell (ITSOFC) and the membrane for high temperature (>500 °C) CO2 separation. This work reviews the recent progresses of these composite materials as ITSOFCs electrolyte and CO2 permeation membrane and reports the latest results of our group. The composite materials, i.e., samarium-doped ceria (SDC)–Li/Na/K2CO3 (43.5/31.5/25 mol%) and SDC–Li/Na2CO3 (50/50 mol%), were prepared and tested as the electrolyte for SOFCs, respectively. The CO2 in the cathode gas enhances the power output. At 650 °C, and with CO2/O2 used as the cathode gas, the fuel cell with SDC–Li/Na2CO3 (50/50 mol%) electrolyte gives a power output 1700 mW cm−2 at a current density 3000 mA cm−2. Another composite material made of Bi1.5Y0.3Sm0.2O3/molten carbonate (Li/Na/K2CO3, 43.5/31.5/25 mol%) was synthesized and used for selective permeation of CO2 at 500–650 °C. The CO2 permeation flux for the dual-phase membrane increases with the increase of temperature and reaches a maximum value of 6.60 × 10−2 mL cm−2 min−1 at 650 °C, with apparent activation energy for CO2 permeation of 113.4 kJ mol−1. These results further demonstrate that the ionic-conducting ceramic/carbonate composite material is an alternative choice as the ITSOFCs electrolyte and high temperature CO2 separation membrane material. The ionic transfer mechanism is discussed.