Syngas production performance and degradation analysis of a solid oxide electrolyzer stack

Abstract

A short stack of the Jülich F10 design with anode-supported cells (ASCs; in fuel cell mode), based on the Jülich design with a lanthanum strontium cobalt ferrite (LSCF) air electrode, was employed for a medium-term co-electrolysis operation in technically-relevant conditions at 800 °C. The feed and product gases for an identically-constructed stack under the same conditions were monitored by a process-grade gas analysis system analyzing all relevant gases, including water per direct measurement. The product gas composition conforms to the expectation based on electrolysis and the reverse water-gas shift (RWGS) reaction for a wide range of conversion ratios. The formation of methane as a by-product is discussed. The degradation for stationary phases of the experiment amounted to ∼2% kh−1 (voltage degradation) and 4% kh−1 (based on area specific resistance (ASR)), respectively. Based on the evaluation of electrochemical impedance spectra and post-mortem analyses, the degradation is induced by the depletion of nickel near the electrolyte interface which must be urgently resolved. A hypothesis for an electrochemical mechanism is postulated that complements existing theories. The mass transport contributes the most to the total impedance and the porosity in our cathodes should be optimized for electrolysis mode.