Fe-Ce_0.1Zr_0.9O₂-Ag electrode for one-step methane synthesis in solid oxide electrolyser

A novel mixed oxide material, Fe-Ce_0.1Zr_0.9O₂-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.