Fe-Ce0.1Zr0.9O2-Ag electrode for one-step methane synthesis in solid oxide electrolyser

A novel mixed oxide material, Fe-Ce0.1Zr0.9O2-Ag, has been tested as cathode, for the very first time, for one-step methane synthesis in a single temperature solid oxide electrolyser by electrolysing a H2/CO2 (4:1 v/v) mixture at 500 °C. Maximum methane selectivity and yield were 6.67 % and 2.66 %, respectively, at an applied potential of 1.6 V (corresponding to a current density of 3.94 mAcm-2). CO2 conversion (~ 40 %) was independent of the applied voltage. However, upon increasing the potential, CO% dropped monotonically with a commensurate increase in methane%. Calculations based on oxide ion removal as a function of current density confirmed that under loaded conditions steam generated in situ (via reverse water gas shift and methanation reactions) got electrolysed to H2, which reacted with CO producing more methane. Such excess methane produced purely electrolytically under loaded conditions matched well with the values predicted theoretically assuming that the decrease in CO% was solely due to enhanced methanation.