Characterization of Pr0.5A0.5Fe0.9W0.1O3−δ (A = Ca, Sr and Ba) as symmetric electrodes for solid oxide fuel cells

Abstract

The effect of doping with alkaline-earth metal cations (A = Ca, Sr and Ba) on the crystal structures of tungsten-doped ferrite-based perovskites (Pr_0.5A_0.5Fe_0.9W_0.1O_3−δ, PAFW, denoted as PCaFW, PSrFW and PBaFW) as the symmetric electrodes for symmetric solid oxide fuel cells (SSOFCs) was investigated. The phase structure, chemical compatibility and thermal expansion with La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM), and electrical conductivity and electrochemical performance in the hydrogen oxidation reduction (HOR) and oxygen reduction reaction (ORR) were carefully investigated. The conclusions show that the divalent alkaline earth metal affects the phase stability under reducing atmospheres, thermal properties and electrochemical performance. PSrFW exhibited excellent electrochemical performance compared to PCaFW, while PCaFW displayed in situ exsolution behavior under reducing atmospheres. To evaluate these materials as symmetric electrodes for solid oxide fuel cells, symmetric cells (PAFW|LSGM|PAFW) were used to investigate the mechanisms of the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) under different reducing and oxidizing atmospheres. The conclusions show that the adsorption and dissociation processes of the surface oxygen and hydrogen adsorption and dissociation are the rate-limiting steps under oxidizing and reducing conditions. Finally, the electrochemical performances (including cell performance, long-term stability and redox stability) of the two candidate samples were also investigated systematically. All conclusions exhibit that the divalent alkaline earth metal has an evident impact on the electro-catalytic activity and electrochemical performance.