Influence of layer numbers on the structural and electrical performance of cobalt-free SrFe_0.5Ti_0.5O_3-δ cathode for ntermediate-temperature solid oxide fuel cell application

The influence of layer numbers on the structural and electrical performance of SrFe_0.5Ti_0.5O_3-δ cobalt-free cathode was studied. The SrFe_0.5Ti_0.5O_3-δ cathode films fabricated using screen-printing technique with different layer numbers sintered at 1300 °C for 2 h were characterised using field-emission scanning electron microscopy (FESEM) for structural analysis and four-point van der Pauw method for direct current electrical conductivity (σ_DC). FESEM micrographs confirmed that the SrFe_0.5Ti_0.5O_3-δ cobalt-free cathode films (fabricated with different layer numbers) adhered well on the samarium doped ceria electrolyte surface. The porous films were also uniform without crack formation. The thicknesses of the as-fabricated cathode films were 9.0 ± 0.5, 25.6 ± 1.0, 54 ± 0.6, 71.2 ± 1.4 and 92.2 ± 1.6 μm for layer numbers 1 (1×), 4, 7, 10 and 13 times (13×), respectively. The electrical performance of SrFe_0.5Ti_0.5O_3-δ cobalt-free cathodes was reported within the operating temperature ranging from 550 °C to 800 °C as the targeted application was the intermediate temperature solid oxide fuel cell. The layer numbers (thickness) dependence of σ_DC suggested a mechanism of long electron pathway at the surface and through the films due to the increase in pores. While the sintering temperature is kept constant, increasing in the number of layers increased the pores accordingly. Hence, the lowest σ_DC value at 800 °C (2.45 S cm⁻1) is obtained for SrFe_0.5Ti_0.5O_3-δ cathode films with high number of layers (13×). The highest σ_DC value (16.46 S cm⁻1) was recorded for a single layer (1×) SrFe_0.5Ti_0.5O_3-δ cathode film. Although the conductivity value was still far from the desired theoretical conductivity of 100 S cm⁻1, this result was better than that of the literature that reported the same composition, thereby showing that the quality of cathode film was improved. (paper)