Heterostructured electrode with concentration gradient shell for highly efficient oxygen reduction at low temperature

Heterostructures of oxides have been widely investigated in optical, catalytic and electrochemical applications, because the heterostructured interfaces exhibit pronouncedly different transport, charge, and reactivity characteristics compared to the bulk of the oxides. Here we fabricated a three-dimensional (3D) heterostructured electrode with a concentration gradient shell. The concentration gradient shell with the composition of Ba0.5-xSr0.5-yCo0.8Fe0.2O3-δ (BSCF-D) was prepared by simply treating porous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) backbone with microwave-plasma. Electrochemical impedance spectroscopy reveals that the oxygen surface exchange rate of the BSCF-D is enhanced by ~250% that of the pristine BSCF due to the appearance of the shell. The heterostructured electrode shows an interfacial resistance as low as 0.148 Ω cm2 at 550°C and an unchanged electrochemical performance after heating treatment for 200 h. This method offers potential to prepare heterostructured oxides not only for electrochemical devices but also for many other applications that use ceramic materials

Self-Transforming Configuration Based on Atmospheric-Adaptive Materials for Solid Oxide Cells

Solid oxide cells (SOC) with a symmetrical configuration have been focused due to the practical benefits of such configurations, such as minimized compatibility issues, a simple fabrication process and reduced cost compared to SOCs with the asymmetrical configuration. However, the performance of SOCs using a single type of electrode material (symmetrical configuration) is lower than the performance of those using the dissimilar electrode materials (asymmetrical configuration). Therefore, to achieve a high-performance cell, we design a 'self-transforming cell' with the asymmetric configuration using only materials of the single type, one based on atmospheric adaptive materials. Atmospheric-adaptive perovskite Pr0.5Ba0.5Mn0.85Co0.15O3-delta (PBMCo) was used for the so-called self-transforming cell electrodes, which changed to layered perovskite and metal in the fuel atmosphere and retained its original structure in the air atmosphere. In fuel cell mods, the self-transforming cell shows excellent electrochemical performance of 1.10Wcm(-2) at 800 degrees C and good stability for 100 h without any catalyst. In electrolysis mode, the moderate current densities of -0.42A cm(-2) for 3 vol.% H2O and -0.62 A cm(-2) for 10 vol.% H2O, respectively, were observed at a cell voltage of 1.3V at 800 degrees C. In the reversible cycling test, the transforming cell maintains the constant voltages for 30 h at +/- 0.2A cm(-2) under 10 vol. % H2O

The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

© The Author(s) 2018Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.Fonds zur Förderung der wissenschaftlichen Forschung (FWF)212921411