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

Abstract

Solid oxide technology allows to produce synthesis gas (CO+H2), a relevant mixture and precursor for e-fuels and other products in the chemical industry. This work reports on the long-term performance of an electrolyte supported cell (Ni-CGO/3YSZ/LSCF-CGO), operating at industrially relevant co-electrolysis conditions (32.5 % H2/35 H2O/8.1 CO/24.4 CO2, -0.5 A/cm2, 816 °C). The applied cell had a Ni-CGO fuel electrode (~30 μm thick), a 3YSZ electrolyte (~90 μm) and an LSCF-CGO oxygen electrode (~35 μm thick) including a thin CGO protective layer.The cell was operated successfully for 2300 h at constant galvanostatic test conditions, with an overall degradation of 80 mΩ cm2/kh, which is a higher degradation rate than the reported for similar cells at comparable conditions. 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 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 falls and stabilizes during the last app. 2 kh of the long-term operation of the cell to 32 mΩcm2/kh. The increase in ohmic resistance is in percentage small but steady at 7 %/kh, while the increase in polarization resistance follows the same trend as the ASR.Electrochemical impedance spectroscopy (EIS) showed a decrease of 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 species was found in the active area of the Ni-CGO fuel electrode.