Mn-substituted titanates as efficient anodes for direct methane SOFCs

A new family of perovskite titanates with formula La4Sr8Ti12−xMnxO38−δ has been investigated as fuel electrode materials for SOFCs. These phases present a rhombohedral (R− 3c) unit cell. Mn substitution does not have a large impact on the bulk conductivity of the phases studied, which remains close to the values observed in other related titanates, although the grain boundary contributions are largely improved. Relatively low polarisation resistances were observed under both hydrogen and methane conditions, e.g., 0.3 and 0.7 Ω cm2 at 950 °C, respectively. Despite the polarisation resistance in methane being more than twice that in hydrogen, the performances are very similar, which might indicate certain methane activation at that temperature. Surprisingly, the anodic overpotential was fairly low compared to those reported in the literature for other materials and especially for titanate-based anodes, i.e., a value of 55 mV at 0.5A/cm2, at 950 °C, under wet hydrogen was obtained. Additionally, a value 72 mV was obtained in the same conditions under methane. These values indicate that the use of Mn as dopant for perovskite-related titanates enhanced electrochemical performance of these anodes, especially at high temperatures.