Bifunctional electrocatalysts Pr0.5Sr0.5Cr0.1Fe0.9−xNixO3−δ (x = 0.1, 0.2) for the HOR and ORR of a symmetric solid oxide fuel cell

Abstract

Pr_0.5Sr_0.5Cr_0.1Fe_0.9−xNi_xO_3−δ (PSCFN_x, x = 0.1, 0.2) catalysts are prepared and utilized as electrodes in symmetric solid oxide fuel cells (SOFCs) for the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). Although the PSCFN_x cathode retains its perovskite phase during operation in SOFCs, the anode is totally decomposed and decorated with an exsolved metallic Ni–Fe alloy (denoted as re-PSCFN_x) in a reducing atmosphere. Electrochemical impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) analysis reveals that the rate-limiting step for the HOR at the anode is the hydrogen adsorption–dissociation process, while the charge transfer process is found to dominate the ORR at the cathode. As the doping of Ni is increased, the cathode polarization resistance for the ORR decreases from 0.19 Ω cm² for PSCFN_0.1 to 0.09 Ω cm² for PSCFN_0.2 at 800 °C in air. A similar trend is observed for the anode polarization resistance for the HOR, which exhibits a reduction from 2.46 Ω cm² of re-PSCFN_0.1 to 1.28 Ω cm² of re-PSCFN_0.2 at 800 °C in H₂. When fueled with hydrogen, a single cell based on the PSCFN_0.2/La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM)(240 μm)/re-PSCFN_0.2 configuration delivers a maximum power density of 623 mW cm⁻² and slight performance degradation when operated for 220 h at 800 °C. Ni doping results in the charge redistribution of B-site ions. Increasing the doping level of Ni results in additional electron transfer channels and oxygen vacancies that adsorb more oxygen species, which facilitates the ORR performance. Furthermore, an increase in the number of Ni–Fe nanoparticles and creation of abundant interfaces in the anode promote the HOR. This work suggests that PSCFN_0.2 has the potential to be an excellent electrode material for a symmetric SOFC.