Highly Durable Cathode Materials with High Performance for Protonic Ceramic Fuel Cells
Authors: Park Ka-Young , Park Jun-Young 
Published: February 2020

Solid oxide fuel cells (SOFCs) have attracted clean alternative power sources because of their have high energy conversion efficiency, multi-fuel flexibility and no use of precious metal catalysts. However, high operating temperatures (800 – 1000 oC) deteriorate the long term durability and fabrication cost of SOFCs [1]. Recently protonic ceramic fuel cells (PCFCs) based on proton-conducting electrolytes may be one of solutions to decrease operating temperatures due to high proton conductivity at intermediate temperature (IT; 400 – 600 oC) [2].
Doped barium zirconate (BZO) and barium cerate (BCO) based electrolytes have been studied extensively for use in PCFCs [3]. Even though BCO exhibits high proton conductivity, it is not suitable owing to its poor CO2 tolerance. On the other hand, BZO shows high chemical stability with good mechanical strength under CO2atmospheres. However, the proton conductivity of BZO-based materials is lower than that of BCO at the IT.
Hence, the compound materials (BZCO) of BZO and BCO have attracted as a candidate electrolyte for PCFCs, BZCO exhibits high proton conductivity as well as maintains good chemical stability. In particular, co-doped BZCO materials with Y and Yb (BaZr0.1Ce0.7Y0.1Yb0.1O3–
δ; BZCYYb) have been reported to exhibit high proton conductivity and the excellent catalytic activity for reforming of hydrocarbons with the conversion of H2S to SO2[3]
For PCFCs, the reactions at the cathode can be expressed as Eq. (1) and water generates at three phase boundaries (TPBs) of cathode side [4]:
(1) 4OH.
o + O2 + 4e- --> 2H2O + 4Ox
o

This phenomenon makes their cathode reactions more complex and results in high cathode polarization resistances. Until now, however, mixed ionic and electronic conductors for oxygen conducting SOFCs have used as the cathode materials for PCFCs, such as Ba0.6Sr0.4Co0.2Fe0.8O3–
δ (BSCF), La0.6Sr0.4Co0.2Fe0.8O3–
δ(LSCF).
Therefore, in this work suitable cathode materials are proposed for highly durable PCFCs with the improved performance. The cathode materials for PCFCs are required to the properties of high electric and ionic conductivity, high catalytic activity, good thermal compatibility with the electrolyte, and chemical stability in a humid oxidizing atmosphere [5-7]. For achieving these goals, several double perovskite-structure cathode materials are investigated under various operating conditions, such as flow rate of gas, amount of humidification and operating temperature in terms of the performance and long-term durability through the use of electrochemical and physicochemical analysis.

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* Corresponding author: jyoung@sejong.ac.kr (J.-Y. Park).