Experimental Deconvolution of Resistance Contributions in Commercial Solid Oxide Cells with Ni-CGO Electrode

Solid oxide cells (SOCs) convert the energy of a fuel to electrical energy (fuel cell mode) and electrical energy into a fuel such as hydrogen (electrolysis mode) with exceptionally high efficiencies (>60% and >90%, respectively). They are flexible in terms of usable fuels & gasses and operating modes such as dynamic and reversible. Therefore, SOCs can be a solution for the intermittent nature of renewable energy sources, which are increasingly implemented in modern energy systems. Among state-of-the-art (SoA) SOCs, electrolyte supported cell (ESC) configurations are in the process of commercialization. They are typically composed of Ni-CGO fuel electrodes, YSZ electrolytes, and an LSCF-CGO air electrode. Key to optimize performance and durability is the detailed knowledge of how the cell components contribute to the total cell resistance, typically obtained through electrochemical impedance analysis. This is a challenge for SoA ESCs, because all the electrode contributions overlap strongly at the low frequency ranges below and around ca. 1 Hz. The present study succeeded with experimentally de-convoluting the different electrode contributions. The approach was to carry out impedance studies on two versions of ESC, one SoA with Ni-CGO and LSCF-CGO electrodes and one with Ni-CGO and LSM-YSZ electrodes, where the frequencies of the air electrode contributions are separated from the fuel electrode contributions.