Analysis of the Long-Term Operation of an Electrolyte-supported Solid Oxide Cell Under Co-electrolysis Regime

Abstract

The solid oxide cell technology allows to produce synthesis gas (CO+H2), a precursor for e-fuels and other chemicals. This work reports on the long-term performance of an electrolyte supported cell (Ni-CGO/3YSZ/LSCF-CGO), operated at industrially relevant co-electrolysis conditions (32.5 % H2, 35 % H2O, 8.1 % CO, 24.4 % CO2, -0.5 A/cm2, 815 °C). The cell had a Ni-CGO fuel electrode (~30 μm thick), a 3YSZ electrolyte (~90 μm) and an LSCF-CGO oxygen electrode (~35 μm thick) plus a thin CGO barrier layer in-between. The cell was operated for 2300 h at constant galvanostatic conditions, with an overall degradation of 80 mΩcm2/kh. At the start of the test, the ohmic resistance contributes to almost 90 % of the ASR (area-specific resistance), but the increase in Rp (polarization resistance) is what contributes the most to the increase in total cell ASR during the long-term operation. This increase in ASR is not constant over the entire test time. On the contrary, it is considerably higher during the first 300 hours (180 mΩcm2/kh) and then it levels off and stabilizes to 32 mΩcm2/kh during the remaining approx. 2 kh of the long-term operation. The measured electrochemical impedance spectra showed a decrease in the performance of the Ni-CGO fuel electrode. A possible explanation for the observed fuel electrode degradation was found via SEM-EDS, where a considerable quantity of silicon-containing compounds was found in the active area of the Ni-CGO fuel electrode.