Abstract
In this work, cobalt and zinc-doped Ce0.8Gd0.2O1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000°C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 °C of pressed Zn-doped samples (6.7x10-2 S/cm) and Co-doped samples (7.5x10-2 S/cm) is similar for undoped samples (7.2x10-2 S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.
Highlights
Solid oxide fuel cell (SOFC) has attracted considerable interest in the last few decades as a promising clean and efficient energy conversion device[1,2,3]
A major difficulty in using ceria as electrolyte is related to the reduction of Ce+4 to Ce+3, which is significant at low oxygen partial pressure (p(O2) < 10-15 atm) and high temperature (T > 800 °C)[6]
The starting materials were CGd (Fuel Cell Materials) with 32.6 m2/g specific surface area, Co(NO3)2.6H2O (Synth, 98% purity), and Zn(NO3)2.6H2O (Synth, 99.98% purity). Appropriate amounts of these powders were mixed in isopropanol containing 1 wt% of poly-vinylbutyral (B-98, Solutia), in a vibratory mill with zirconia milling media
Summary
Solid oxide fuel cell (SOFC) has attracted considerable interest in the last few decades as a promising clean and efficient energy conversion device[1,2,3]. Classical designs employ yttria-stabilized zirconia (YSZ) as electrolyte, but it exhibits adequate ionic conductivity only at high temperatures (900-1000 °C). Such high temperatures limit the viability of fuel cells due to long-term stability and require expensive materials for sealing, insulation, and interconnects. A major difficulty in using ceria as electrolyte is related to the reduction of Ce+4 to Ce+3, which is significant at low oxygen partial pressure (p(O2) < 10-15 atm) and high temperature (T > 800 °C)[6] Another drawback regarding ceria solid solutions is their poor sinterability, which requires high temperatures (1400-1600 °C) to achieve high densification (> 95%)[5]. Platinum paste electrodes were applied on both sides of the pellets
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