Optimization of La_0.2Sr_0.7–xCa_xTi_0.95Fe_0.05O_3−δ Fuel Electrode Stoichiometry for Solid Oxide Fuel-Cell Application

Abstract

Development of active ceramic hydrogen electrodes with high stability is an important challenge for developing solid oxide fuel cells (SOFC). Herein, a set of cubic perovskite-type La/Ca/Fe-doped strontium titanates, La 0.2 Sr 0.7−x Ca x Ti 0.95 Fe 0.05 O 3-δ (LSCTF), was synthesized. Their crystallographic and electrical properties, catalytic activity, and stability, as well as performance as fuel electrodes in the solid oxide fuel cell (SOFC) have been evaluated. It was confirmed by the results that the LSCTF behave like semiconductors, and the conductivity, catalytic activity, and stability of the electrodes significantly depend on the Ca concentration in the A-site. In the case of an optimal composition of the La 0.2 Sr 0.35 Ca 0.35 Ti 0.95 Fe 0.05 O 3−δ fuel electrode, a polarization resistance value of 0.21 Ω cm 2 at 850 °C in a humidified (1.7% H 2 O) H 2 atmosphere was obtained. During the stability test, the fuel cell with the 50 wt % La 0.2 Sr 0.35 Ca 0.35 Ti 0.95 Fe 0.05 O 3−δ + 50 wt % Ce 0.9 Gd 0.1 O 2−δ anode showed a power density of 322 mW cm −2 at 850 °C in a 98.3% H 2 + 1.7% H 2 O atmosphere.

Preparation of SOFC Anodes at Lower Temperature with Boosted Electrochemical Performance

“…Obviously, the R p value of the LCTNi single cell is much smaller than that of the LCTNi-ss single cell under the same H 2 partial pressure. The polarization resistances are comparable to those of CaTiO 3 - or SrTiO 3 -based perovskites and Ni/YSZ anode single cells reported in the literature, ,− as listed in Table .…”

Influence of A-Site Modifications on the Properties of La0.21Sr0.74−xCaxTi0.95Fe0.05O3−δ Based Fuel Electrode for Solid Oxide Cell

“…These results confirm that increasing for Ca concentration leads to the decrease of LSCTF5-x unit cell volume, similarly as in the case of LSCTF10-x. 35,39 SEM micrographs of LSCTF5-26, LSCTF5-48 and LSCTF5-69 pellet surfaces after sintering at 1250 °C for 5 h in the air were recorded and are presented in Fig. 2.…”

“…The properties of LSCTF5-x, described in this study have been compared to properties of La 0.2 Sr 0.7-x Ca x Ti 0.95 Fe 0.05 O 3−δ (LSCTF10-x) with 10% A-site deficiency with exactly the same La/Sr/Ca ratios as well as the same techniques used for synthesis and testing of the electrodes. 35 Experimental Materials synthesis.-The raw powders for preparing of La 0.21 Sr 0.74−x Ca x Ti 0.95 Fe 0.05 O 3−δ (LSCTF5-x with 5% A-site deficiency) (x = 0.26 -0.69 and represent the amount of Ca in lattice) fuel electrodes were synthesized by using the glycine-nitrate combustion synthesis method from the high-purity starting chemicals of La(NO 3 ) 3 .6H 2 O (99.9%, Alfa Aesar), Sr(NO 3 ) 2 (99.9%, Alfa Aesar), Ca(NO 3 ) 2 .4H 2 O (99.9%, Alfa Aesar), Fe(NO 3 ) 3 .9H 2 O (99.9%, Alfa Aesar) and C 6 H 22 N 2 O 8 Ti 50% solution in water (Sigma-Aldrich) and glycine (99%, Sigma Aldrich) as reducing agent. The mole ratio of the nitrate to glycine was fixed at 1:0.7.…”

“…Table I shows the exact stoichiometry of 5% A-site deficient powders synthesised in this study (LSCTF5-x) and powders with 10% A-site deficiency (LSCTF10-x) synthesized, characterized and analyzed using the same protocol and equipment. 35 The proportions of La, Sr and Ca are same in both experimental sets only different the magnitude of A-site deficiency has been considered.…”

Probing Oxide Ion Conductivity in Na0.5Bi0.5TiO3–BiFeO3–BaTiO3-Based Ferroelectric Materials

“…Electrochemical energy devices convert chemical energy into electrical energy by oxidizing fuels such as hydrogen, ammonia, methane, biogas, and hydrocarbons as well as natural gas. − Oxide ionic conductors have shown key technological applications in sensors, oxygen separation membranes, and catalysts. ,− Solid oxide fuel cells (SOFCs) can offer a high conversion efficiency of 60–80%, longer durability, fuel flexibility, and are eco-friendly. , However, SOFCs require high operational temperatures (>850 °C) as the state-of-the-art electrolytes, e.g. , Y 0.2 Zr 0.8 O 1.9 (YSZ) show good Oxide ion conductivity at elevated temperatures (0.14 S cm –1 at 1000 °C) .…”