Effect of Boron Deposition and Poisoning on the Surface Exchange Properties of LSCF Electrode Materials of Solid Oxide Fuel Cells

Abstract

The relationship between the surface segregation, boron poisoning and surface exchange coefficients of La0.6Sr0.4Co0.2Fe0.8O3−δ, (LSCF) cathodes of solid oxide fuel cells (SOFCs) is studied on dense bar samples using SEM, SIMS and conductivity relaxation method. The SEM results clearly indicate that the segregation on the LSCF surface occurs after heat-treatment at 700–800°C for 48 h, forming isolated particles on the LSCF surface. The presence of volatile boron species accelerates grain growth of the segregated particles and reacts with LSCF. The depth of boron reaction layer after heat-treatment in the presence of E-glass at 700°C, 750°C and 800°C for 48 h was 2, 5 and 40 nm, respectively. The depth profiles analysis of SIMS indicates that there is segregation and enrichment of constituent elements of LSCF on the electrode surface, in line with the depth profile of boron species on the LSCF sample surface layer. Boron deposition and poisoning deteriorates the surface exchange and diffusion processes for the oxygen reduction reaction on LSCF. After exposed to boron at 800°C for 48 h, the surface exchange coefficient, Kchem is 6.0 × 10−5 cm s−1, more than one magnitude lower than 1.1 × 10−3 cm s−1 of as-prepared LSCF samples.

Sulfur Deposition and Poisoning of La0.6Sr0.4Co0.2Fe0.8O3-δCathode Materials of Solid Oxide Fuel Cells

“…1). 22 After heat-treatment in the absence of SO 2 , there is a clear formation of isolated small particles on the LSCF surface. As the heat-treatment temperatures decreased to 600 • C-400 • C, peaks associated with SrSO 4 phase disappear and a distinct peak at 29.5 • was detected (curves e,f,g, Fig.…”

“…21,22 The results indicate that the deposition of sulfur species on the LSCF surface and formation of S-containing compounds such as SrSO 4 and SrS depends strongly on the temperature, and becomes most pronounced at temperatures around 700 • C. Use of dense bar samples will facilitate the observations of microstructure changes and surface property characterizations.…”

Controlling the reaction between boron-containing sealing glass and a lanthanum-containing cathode by adding Nb2O5

“…It is known that it is the loss of volatile boron compounds from sealing glass-ceramics that leads to the formation of LaBO 3 on the cathode surface [7,8,17]. To investigate the volatility of these compounds in sealing glass-ceramics, the accumulated weight change of glass-ceramics in dry air at 750 C was measured as a function of time for up to 1000 h, as shown in Fig.…”

Chromium deposition and poisoning of La 2 NiO 4 cathode of solid oxide fuel cell

“…After calcination at 950°C for 3 h, the as-prepared powders were confirmed by X-ray diffraction (XRD) to be single-phase, tetragonal La 2 NiO 4 . La 2 NiO 4 powders were then pressed into a rectangular bar at 300 MPa and sintered at 1350°C for 4 h in air to form dense La 2 NiO 4 bar with relative density higher than 96%, which was satisfied with the requirement of electrical conductivity relaxation (ECR) method [21]. The size of the sintered La 2 NiO 4 bar samples had dimension of 25 mm × 6.6 mm × 0.62 mm.…”