Highly Active and Stable Cobalt-Free Hafnium-doped SrFe0.9Hf0.1O3-δ Perovskite Cathode for Solid Oxide Fuel Cells

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs). Here we report a Co-free Hf-doped SrFe0.9Hf0.1O3-delta (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO2 poisoning compared to undoped SrFeO3-delta. The SFHf cathode has a polarization area-specific resistance as low as 0.193 Omega cm(2) at 600 degrees C in a SFHflSm(0.2)Ce(0.8)O(1.9) (SDC)ISFHf symmetrical cell and has a maximum power density as high as 1.94 W cm(-2) at 700 degrees C in an anode-supported fuel cell (Ni+(ZrO2)(0.92)(Y2O3)(0.08) (YSZ)vertical bar YSZ vertical bar SDC vertical bar SFHf). The ORR activity maintains stable for a period air and in CO2-containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO3-delta by decreasing oxygen vacancy concentration and increasing metal oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs.