Abstract
Borosilicate glass and glass-ceramics are the most common sealant materials for planar solid oxide fuel cells (SOFCs). This study focuses on the fundamentals of deposition and poisoning of volatile boron species from the borosilicate glass on the electrocatalytic activity and microstructure of La0.8Sr0.2MnO3 (LSM) cathodes under accelerated SOFC operation conditions, using EIS, SEM, FIB-SEM, HRTEM, NanoSIMS, XPS and ICP-OES. The presence of boron species poisons and deteriorates the electrochemical activity and stability for the O2 reduction reaction on the LSM cathodes. Boron deposition occurs randomly on the LSM electrode surface under open circuit but is driven to the electrode/electrolyte interface region under cathodic polarization conditions, resulting in the formation of LaBO3 and Mn2O3 and the disintegration of the LSM perovskite structure. The preferential boron deposition at the interface is most likely due to the increased activity of the highly energetic lanthanum at LSM lattice sites at the three phase boundary region under cathodic polarization conditions, accelerating the reaction rate between the gaseous boron species and energetic La. This study provides a fundamental insight into the boron deposition and its interaction with SOFC cathodes.
Highlights
Glass pellet Pt mesh Cathode Electrolyte PtSimilar to that used in the chromium studies.[24] The direct contact between glass and cathode is avoided by using a platinum mesh as the buffer layer (Scheme 1b)
Solid oxide fuel cells (SOFCs) are an energy conversion device to directly transfer the chemical energy of fuels to electrical energy, and are the most efficient and least polluting energy conversion technology among various kinds of fuel cells
The results show that boron deposition is related to the activity of lanthanum at the LSM lattice, which in turn is related to the O2 reduction reaction at the electrode/electrolyte interface region
Summary
Similar to that used in the chromium studies.[24] The direct contact between glass and cathode is avoided by using a platinum mesh as the buffer layer (Scheme 1b) In this way volatile boron species can only deposit on the cathode via gas phase diffusion. The electrode activity and stability of LSM cathode are investigated in the presence of borosilicate glass under open circuit and cathodic polarization operation conditions. The electrochemical performance of LSM electrodes was measured in the absence of glass pellet. Microstructure observation and elemental mapping analysis of the wafer sample were carried out using both HITACHI MI4000L and scanning/high-resolution transmission electron microscopy (STEM/HRTEM, JEOL JEM-ARM200F, 200 kV) equipped with energy dispersive X-ray spectroscopy (EDS) detectors. Secondary ion images were obtained by rastering the primary ion beam across areas measuring 30–50 μm,[2] at a resolution of 256 × 256 pixels, with dwell times of 90 ms per pixel
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