Electrochemical performance and redox stability of Sr_0.8La_0.2TiO₃-Ce_0.9Gd_0.1O_2-δ composite anodes for solid oxide fuel cells

Sr_0.8La_0.2TiO₃-Ce_0.9Gd_0.1O_2-δ (SLT-GDC) composite anodes were synthesized by solid state reaction and the effect of percolation on electro-catalytic activity and redox stability was investigated. The percolation threshold of Sr_0.8La_0.2TiO₃ and Ce_0.9Gd_0.1O_2-δ in the composite calculated based on the Kusy’s percolation theory is 10.7 vol.% and 17.4 vol.%, respectively. The area specific resistance (ASR) of the SLT-GDC composite anode at 800 °C in H₂ decreased up to 15 vol.% GDC in a SLT matrix because GDC has a much higher electro-catalytic activity than SLT. However, the samples which showed GDC percolation, including samples with 20 and 33 vol.% GDC in a SLT matrix, showed very high ASR values. The lowest ASR value was obtained for the anode with 15 vol.% GDC in a SLT matrix because this anode showed a mixed percolation region and had good connectivity to both electronic and ionic compounds. Moreover, the anode with the 15 vol.% GDC in a SLT matrix has very stable activity with a deviation of only 0.5% in ASR during repeated redox cycling.