Xuanlin Lu,Zhi Yang,Jian Zhang,Xin Zhao,Jiaxuan Chen,Wen Liu,Yicheng Zhao,Yongdan Li
Oxygen reduction and proton conduction originated from hydration are two key steps in the cathode process of protonic ceramic fuel cells. In this work, Pr 6 O 11 is impregnated into a cobalt-free BaCe 0.2 Fe 0.8 O 3-δ cathode, resulting in an improved activity of lattice oxygen and a moderate enhancement of the electrical conductivity, both of which are beneficial for charge transfer, the rate-determining step of oxygen reduction process at the cathode. The polarization resistance of bare BaCe 0.2 Fe 0.8 O 3-δ cathode for oxygen reduction is 0.115 Ω cm 2 at 700 °C, which is reduced significantly to 0.039 Ω cm 2 with the addition of 30 wt% Pr 6 O 11 . Besides, the hydration ability of the cathode is also improved with Pr 6 O 11 , and thus the combination of proton and oxygen is facilitated. A single cell with 30 wt% Pr 6 O 11 -70 wt% BaCe 0.2 Fe 0.8 O 3-δ composite cathode exhibits the highest maximum power density of 1406 mW cm −2 at 700 °C. The composite cathode also shows a good stability.
Xin Zhou,Nianjun Hou,Tian Gan,Lijun Fan,Yongxin Zhang,Jingyu Li,Ge Gao,Yicheng Zhao,Yongdan Li
BaCe 0.2 Fe 0.8-x Pr x O 3-δ (x = 0–0.3) is studied as a cobalt-free cathode material for proton-conducting solid oxide fuel cells. The cathode is composed of a cubic BaFeO 3-δ phase and an orthorhombic BaCeO 3-δ phase, and Pr is doped in both phases. The partial substitution of Pr for Fe decreases the content of the BaFeO 3-δ phase, leading to a lower electrical conductivity . BaCe 0.2 Fe 0.6 Pr 0.2 O 3-δ has the most adsorbed oxygen and Fe 3+ on the surface, resulting in the fastest oxygen surface exchange kinetics and the highest activity. The partial pressure of H 2 O shows a negligible effect on the polarization resistance of the cathode. In contrast, the polarization resistance increases remarkably with the decrease of oxygen partial pressure , indicating that the rate of the cathode process is controlled by the surface exchange of oxygen. At 700 °C, BaCe 0.2 Fe 0.6 Pr 0.2 O 3-δ shows the lowest polarization resistance of 0.057 Ω cm 2 , and a single cell with that cathode exhibits the highest maximum power density of 562 mW cm −2 . The results demonstrate that Pr doped BaCe 0.2 Fe 0.8 O 3-δ is a promising cobalt-free cathode material for proton-conducting solid oxide fuel cells.
Shihang Guo,Lin Wang,Chenyang Xue,Sumei Lin,Tingxuan Yi,Yuwen Zhu,Donglin Han
Protonic ceramic cells (PCCs) can convert the energy between electricity and fuels efficiently, and are attracting increasing attention. However, the development of PCCs is restricted by the lack of proper positrode materials. In this work, we report a Co-free system with a nominal composition of BaCe 0.2 Fe 0.8 O 3-δ , which is composed of a Fe-rich matrix phase decorated with Ce-rich nanoparticles. The performance of such a dual-phase positrode system is further improved by doping Zn and/or Ni to increase bulk and surficial concentration of oxygen vacancies. The hydration reaction and surficial adsorption of oxygen species are thereby promoted, benefitting the oxygen reduction reaction. The Ni and Zn co-doped composition Ba(Ce 0.2 Fe 0.8 ) 0.85 (Ni 0.5 Zn 0.5 ) 0.15 O 3-δ exhibits lower polarization resistance than the pristine and singly doped systems, enabling the fuel cells to show high peak power densities of 400, 721, and 828 mW cm −2 at 550, 600, and 650 °C, respectively.
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