Enhanced production of methane through the use of a catalytic Ni–Fe pre-layer in a solid oxide co-electrolyser

A composite cermet consisting in a Ni–Fe alloy and Ce0.9Gd0.1O2-x (CGO) was prepared and used as an electrocatalytic pre-layer in a conventional solid oxide electrolyser (SOEC) for the co-electrolysis of H2O and CO2. The electrocatalyst showed two main phases ascribed to trevorite (NiFe2O4, 78 wt %) and metallic Ni (22 wt %) and an average crystallite size of 27 nm. The role of the Ni–Fe electrocatalyst in promoting CH4 formation was analysed by comparing gas-chromatographic and electrochemical results obtained for coated and bare cells. A slight increase of series resistance was observed for the coated cell (0.85 vs 0.53 Ω cm2) at 525 °C. However, the coated cell demonstrated an enhanced CH4 production in the entire temperature range investigated (525–800 °C). Contrarily to what observed for the bare cell which mainly produced syngas, the coated cell allowed to achieve a high yield of methane (between 67% at 525 °C and 35% at 800 °C) with selectivity to CH4 between 94% at 525 °C and 51% at 800 °C. The selectivity to CO for the coated cell was relatively low (between 6% at 525 °C and 48% at 800 °C). Whereas, the bare cell showed 98–100% selectivity to CO along the entire temperature range). Durability studies showed the possible occurrence of delamination issues as consequence of carbon formation at the interface between the supporting cathode and the electrolyte as observed from the morphological analysis of SOEC cells after operation.