Catalyst-Coated PrBa0.8Ca0.2Co2O5+Δ Cathode with High Cr-Poisoning Tolerance for Intermediate-Temperature Solid Oxide Fuel Cells

Abstract

Intermediate-temperature solid oxide fuel cells (IT-SOFCs) have potential to be a very promising technology for direct conversion of a wide variety of fuels to electricity. However, the commercialization of IT-SOFCs is hindered by several technical challenges. For example, volatile chromium species from interconnect materials often accumulates on the cathode surface or the cathode/electrolyte interface[1], resulting in degradation in electro-catalytic activity for oxygen reduction reaction (ORR) of the cathode. Further, the presence of water vapor can exacerbate the effect of Cr poisoning[2]. Thus, the development of a cathode material with high resistance to Cr poisoning in the presence of water is urgently needed. Recently, a double perovskite PrBa0.8Ca0.2Co2O5+δ (PBCC) cathode with high ORR activity and excellent tolerance against CO2 has attracted much attention[3]. However, its tolerance to Cr poisoning and long-term durability under realistic operating conditions are yet to be characterized. Inspired by our previous studies [4], a number of catalysts are used to modify the surface of PBCC cathode in order to enhance its tolerance to Cr poisoning. As shown in Figure 1a, the measured apparent ORR activation energy is ~1.09 eV for the bare PBCC cathode, as determined from the slope of the Arrhenius plots of kinetics studies. The apparent activation energies for PBCC cathode infiltrated with Ce0.8Sm0.2O1.9 (SDC), La2NiO4 (LN), Ba0.5Co0.5Ox (BaCo), PrOx, and PrNi0.5Mn0.5O3 (PNM) are 0.98 eV, 0.86 eV, 0.87 eV, 0.91 eV, and 0.91 eV, respectively. PBCC coated with La2NiO4 shows the lowest activation energy. As shown in Figure 1b, PBCC cathodes coated with La2NiO4 and Ba0.5Co0.5Ox also show better durability than bare PBCC and other cathodes towards Cr-poisoning (even when the water content was ~7 v%). For instance, the polarization resistance (Rp) of the bare PBCC cathode increased from 0.056 Ω·cm2 to 0.235 Ω·cm2 after operation at 650℃ for ~220 hours in air with 3 v% H2O and then for 140 hours in air with 7 v% H2O; in contrast, the Rp for the Ba0.5Co0.5Ox-coated PBCC cathode remained less than 0.050 Ω·cm2 under the same testing conditions. Among all electrodes studied, La2NiO4 and Ba0.5Co0.5Ox coated PBCC cathodes show the best durability against Cr-poisoning. Figure 1