Evaluation of LnCaCoO_4+δ as Potential Cathode Materials for Solid Oxide Fuel Cells

Abstract

To realize solid oxide fuel cells (SOFCs) operating in 500−700 °C, it is imperative to cultivate innovative cathodes endowed with elevated electrochemical properties. Herein, a series of rare-earth oxides LnCaCoO 4+δ (LnCCO, Ln = Pr, Nd, Sm) are synthesized and assessed as possible SOFC cathodes. The crystal structure, oxygen adsorption and desorption behavior, electrochemical activity, and oxygen reduction reaction kinetics of the LnCCO are systematically characterized. LnCCO adopts a tetragonal crystalline structure with an I4/mmm spatial symmetry group. The measurement results show that both the cell volume and the conductivity of LnCCO increase gradually with the enlargement of the rare-earth element radius. The results of XPS and iodometric titration confirm the monotonic increase of interstitial oxygen content and the surface oxygen adsorption ability, when the rare-earth element changes from Sm to Pr in LnCCO. The electrochemical measurement results show that the polarization resistance of PrCaCoO 4 is 0.048 Ω cm 2 at 700 °C, and the anode-supported cell demonstrates a maximum peak power density of 852 mW cm 2 at 700 °C when utilizing dry H 2 as the fuel source. The oxygen partial pressure-dependent study proves that the rate-limiting step for ORR on a PrCCO cathode is the adsorption dissociation process of surface oxygen molecules.