DRT-based electrochemical investigation on the fuel electrode in a Molten Carbonate Electrolysis Cell

This study aims to understand the electrochemical sub-processes occurring at Molten Carbonate Electrolysis Cell (MCEC) components, focusing on the Nickel (hydrogen) electrode. While hydrogen electrodes in molten carbonate cells have been extensively studied in fuel cell mode, the same cannot be said for electrolysis operation. Addressing this gap is essential for enhancing cell performance under electrolysis conditions. In this work, electrode impedance was evaluated across a broad range of temperature and gas composition. The impedance spectra have been analyzed through the distribution function of relaxation times, which enabled the separation of four polarization loss mechanisms within the Ni electrode based on their characteristic time constants. The main process, at about 10 Hz, exhibits a systematic dependency on H2O and CO2 variation and thus it can be attributed to mass transport losses. This is a critical mechanism for the reaction rate-determining step, as it corresponds to the mass transfer of reactants at the triple-phase boundary, where the water reduction reaction occurs. Results obtained from the oxygen electrode confirm this assumption. To the authors’ knowledge, this study is the first to apply the DRT approach to MCEC technology, providing deeper insights into the origins of the polarization processes that influence electrode performance.