Strategic Design of “Three-in-One” Cathode Toward Optimal Performance of Proton-Conducting Solid Oxide Fuel Cell: The Temperature Matters

Abstract

“Three-in-one” cathode, achieved via B-site heavy-doping of transition elements (typically Co, Fe) into proton-conductive perovskite, holds promise for enhancing the performance of proton-conducting solid oxide fuel cell (H-SOFC) operated below 650°C for electricity generation. However, its electrochemical behavior above 650°C, essential for improving the efficiency of H-SOFC for fuel conversion, remains insufficiently explored. It is still challenging to propose guidance for the design of “three-in-one” cathode toward optimal H-SOFC performance below and above 650°C, with the prerequisite of gaining a comprehensive understanding of the roles of Co and Fe in determining the H-SOFC performance. This work is to address this challenge. Through theoretical/experimental studies, Co is identified to play a role in improving the oxygen reduction reaction (ORR) activity while Fe plays a role in facilitating the cathode/electrolyte interfacial proton conduction. Therefore, if the operating temperature is above 650°C, lowering the Co/Fe ratio in “three-in-one” cathode becomes crucial since the limiting factor shifts from ORR activity to proton conduction. Implementing this strategy, the SOFC using BaCo_0.15Fe_0.55Zr_0.1Y_0.1Yb_0.1O_3−δ cathode achieves peak power densities of 1.67 W cm⁻² under H-SOFC mode at 700°C and 2.32 W cm⁻² under dual ion-conducting SOFC mode at 750°C, which are the highest reported values so far.

Keywords

“three-in-one” / Co/Fe ratio / oxygen reduction reaction (ORR) / proton conduction / proton-conducting solid oxide fuel cell (H-SOFC)

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