Abstract
For an efficient high-temperature reversible solid oxide fuel cell (RSOFC), the oxygen electrode should be highly active for the conversion between oxygen anions and oxygen gas. CaMnO(3-δ) (CM) is a perovskite that can be readily reduced with the formation of Mn(3+) giving rise to oxygen defective phases. CM is examined here as the oxygen electrode for a RSOFC. CaMn(0.9)Nb(0.1)O(3-δ) (CMN) with Nb doping shows superior electric conductivity (125 S cm(-1) at 700 °C) compared with CM (1-5 S cm(-1) at 700 °C) in air which is also examined for comparison. X-ray diffraction (XRD) data show that CM and CMN are compatible with the widely used yttria-stabilized zirconia (YSZ) electrolyte up to 950 °C. Both materials show a thermal expansion coefficient (TEC) close to 10.8-10.9 ppm K(-1) in the temperature range between 100-750 °C, compatible with that of YSZ. Polarization curves and electrochemical impedance spectra for both fuel cell and steam electrolysis modes were investigated at 700 °C, showing that CM presented a polarization resistance of 0.059 Ω cm(2) under a cathodic bias of -0.4 V while CMN gave a polarization resistance of 0.081 Ω cm(2) under an anodic bias of 0.4 V. The phase stability up to 900 °C of these materials was investigated with thermogravimetric analysis (TGA) and variable temperature XRD.
Highlights
Renewable energy sources have attracted much attention in recent years to reduce the dependency on fossil fuels that cause pollutant gas emission and climate change.[1]
A reversible solid oxide fuel cell (RSOFC) that incorporates the production of H2 fuel from electricity via a solid oxide electrolysis cell (SOEC) and electricity generation via a solid oxide fuel cell (SOFC) could be an efficient and low-cost solution for energy conversion and storage
Dense pellets of dilatometry measurement were obtained by calcining the ball-milled powder at 1300 C for 20 hours and cooling to room temperature at 1 C minÀ1 to avoid any cracking during the cooling process
Summary
Renewable energy sources have attracted much attention in recent years to reduce the dependency on fossil fuels that cause pollutant gas emission and climate change.[1]. Dense pellets of dilatometry measurement were obtained by calcining the ball-milled powder at 1300 C for 20 hours and cooling to room temperature at 1 C minÀ1 to avoid any cracking during the cooling process. For the compatibility test between the materials and YSZ, the 1.0 g powder of CM(N) and 1.0 g YSZ was agate-mixed, pressed under 150 MPa and calcined at 950 C for 5 hours at a ramp rate of 10 C minÀ1. A symmetrical cell contains two identical oxygen electrodes on both sides of the 8YSZ electrolyte of 1.8 mm in thickness and 2 cm in diameter. The Ni(O)–YSZ fuel electrode (13 mm in diameter) was prepared by screen printing of the slurry containing 55 wt% NiO and 45 wt% YSZ onto the electrolyte plus a ring at 1350 C for 3 hours. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the powders and tested samples are taken on a Jeol 6700F microscope and Jeol 2011, respectively
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