Abstract
Lanthanide nickelate Ln2NiO4+δ (Ln = La, Pr, or Nd) based mixed ionic and electronic conducting (MIEC) materials have drawn significant attention as an alternative oxygen electrode for solid oxide cells (SOCs). These nickelates show very high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values and hence exhibit good electrocatalytic activity. Earlier reported results show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) leads to an enhancement in the transport and electrochemical properties of the material. Herein, we perform the substitution at A-site with Sr, i.e., La2−xSrxNi0.8Co0.2O4+δ, in order to further investigate the structural, physicochemical, and electrochemical properties. The structural characterization of the synthesized powders reveals a decrease in the lattice parameters as well as lattice volume with increasing Sr content. Furthermore, a decrease in the oxygen over stoichiometry is also observed with Sr substitution. The electrochemical measurements are performed with the symmetrical half-cells using impedance spectroscopy in the 700–900 °C temperature range. The total polarization resistance of the cell is increased with Sr substitution. The electrode reaction mechanism is also studied by recording the impedance spectra under different oxygen partial pressures. Finally, the kinetic parameters are investigated by analyzing the impedance spectra under polarization. A decrease in exchange current density (i0) is observed with increasing Sr content.
Highlights
The increase in greenhouse gases due to fossil fuels, as well as the growing demand for energy, has resulted in a corresponding need for alternative energy sources
The oxygen over stoichiometry (δ-value) of all La2−x Srx Ni0.8 Co0.2 O4+δ (LSNCO) compounds was determined by performing Thermo-Gravimetric Analysis (TGA) experiments under reducing conditions (Ar−4% H2 atmosphere, with a slow heating rate of 0.5 ◦ C·min−1 ) after the samples were equilibrated in air
It is clear that the cell and LSNCO10, the impedance spectra were fitted with four R//CPE along with the Rs overpotential is increased with increasing Sr content
Summary
The increase in greenhouse gases due to fossil fuels, as well as the growing demand for energy, has resulted in a corresponding need for alternative energy sources. Sr-segregation as well as phase change from rhombohedral to cubic, which results in deterioration of the electrode performance, especially during long-term operation [22–24] To avoid such issues, lanthanide nickelates Ln2 NiO4+δ (Ln = La, Pr, or Nd) based oxygen over stoichiometric materials with a K2 NiF4 -type structure are considered as an alternative oxygen electrode. These nickelates are attractive owing to their high oxide ion diffusivity (D*), surface exchange kinetics (k*), as well as high electro-catalytic activity [16–18,25–27]. The electrochemical characterization of these materials is carried out by fabricating symmetrical half-cells
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