Performance of ionic-conducting ceramic/carbonate composite material as solid oxide fuel cell electrolyte and CO 2 permeation membrane

Abstract

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) CO 2 separation. This work reviews the recent progresses of these composite materials as ITSOFCs electrolyte and CO 2 permeation membrane and reports the latest results of our group. The composite materials, i.e., samarium-doped ceria (SDC)–Li/Na/K 2CO 3 (43.5/31.5/25 mol%) and SDC–Li/Na 2CO 3 (50/50 mol%), were prepared and tested as the electrolyte for SOFCs, respectively. The CO 2 in the cathode gas enhances the power output. At 650 °C, and with CO 2/O 2 used as the cathode gas, the fuel cell with SDC–Li/Na 2CO 3 (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 Bi 1.5Y 0.3Sm 0.2O 3/molten carbonate (Li/Na/K 2CO 3, 43.5/31.5/25 mol%) was synthesized and used for selective permeation of CO 2 at 500–650 °C. The CO 2 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 CO 2 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 CO 2 separation membrane material. The ionic transfer mechanism is discussed.