Structural characterization and electrical/electrochemical studies of Nd1-xBaxCo1-y(Fe, Ti)y O3-δ (0 ≤ x ≤ 0.3, y = 0, 0.2) materials as cathode for SOFCs application

Abstract

Perovskite oxide powders of Nd1-xBaxCo1-y (Fe, Ti)y O3-δ (0 ≤ x ​≤ ​0.3, y ​= ​0, 0.2) were synthesized by combustion technique and investigated as cathode materials for SOFCs application. The Rietveld refinement of the XRD data confirms the formation of single phase orthorhombic perovskite structure of Pbnm space group within the compositions (0 ​≤ ​x ​≤ ​0.1, y ​= ​0, 0.2). The microstructural studies revealed the grains generated are irregular in shape and non uniform in size in the micrometer range. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Co3+/Co4+, Fe3+/Fe4+, Ti4+/Ti3+ and O-Lattice/O-Chemisorbed/O-physisorbed species. The measured average CTE values are varies from 18–25 ​× ​10−6 ​K−1 in the temperature range 200–900 ​°C for all the synthesized samples. The electrical conductivity values are found to be 252 Scm−1, 308 Scm−1, 157 Scm−1 at 700 ​°C for the compositions Nd0.9Ba0·1CoO3-δ (NBC 0.1), Nd0.9Ba0·1Co0·8Fe0·2O3-δ (NBCFO), Nd0.9Ba0·1Co0·8Ti0·2O3-δ (NBCTO), respectively. XRD analysis reveals no chemical reactivity for the compositions NBCFO, NBCTO with 20 ​mol% gadolinium doped ceria oxide (Ce0.8Gd0.2O2−δ) electrolyte material after firing at 1200 ​°C for 8 ​h. The area specific resistances (ASR) were calculated for the symmetrical cells and are found to be 0.67 ​Ω ​cm2, 1.07 ​Ω ​cm2 at 850 ​°C for the NBCFO, NBCTO compositions, respectively. Among the compositions evaluated Nd0.9Ba0·1Co0·8Fe0·2O3-δ showed highest total electrical conductivity ~308 Scm−1 and lowest ASR value ~0.67 Ωcm2 compared to all other compositions. Hence the result suggests the synthesized Nd0.9Ba0·1Co0·8Fe0·2O3-δ composition could be a promising cathode material for SOFCs application. © 2020 Elsevier Inc.