Modified NiO/GDC Cermets as Possible Cathode Electrocatalysts for H2O Electrolysis and H2O/CO2 Co-Electrolysis Processes in SOECs

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H2O electrolysis constitutes a promising method for the production of pure-H2 and O2 by using electrical energy. One characteristic and recent application of this technology is electrolysis at high temperatures, by using Solid Oxide Electrolysis Cells (SOECs). Specifically, the electrical energy that is required for the high temperature (600-1000 oC) H2O electrolysis process, is much lower than the energy required at low temperatures (<100 oC), which as a result yields significantly higher efficiency and performance in the former case [1]. Although this technological application has considerable advantages, it confronts many problems that prevent the widespread use and commercialization. One of the most important is the deactivation of the fuel electrodes (H2O/H2), which is usually ascribed to nickel re-oxidation and/or agglomeration during H2O electrolysis, or/and carbon deposition during H2O/CO2 co-electrolysis [2]. Another disadvantage is the degradation/delamination of the oxygen electrodes. Consequently, recent research activities focus on the development and investigation of new, tolerant fuel (H2O/H2) and air electrodes. The aim of this work is the development and study of ceramo-metallic electrocatalysts/electrodes, which are based on commercial NiO/GDC powder (Marion Technologies). This powder is modified with chemical methods by the addition of Ba, Au or/and Mo. The Au or/and Mo modified electro-catalysts have been extensively studied, from our research group, as electrodes in Solid Oxide Fuel Cells (SOFCs) applications [3,4] and their use in SOECs, as H2/H2O electrodes (cathodes), is also very interesting. Furthermore, the modification with Ba aims to the protection of the Ni properties, towards the potential limitation of fast re-oxidation or/and agglomeration. All cermets were investigated through physicochemical characterization with the methods of BET, XRD, XPS, TGA-MS, H2-TPR, O2-TPO, including specific redox stability measurements under various H2O-H2 feed conditions. The powders were also used for the preparation of appropriate paste, which was deposited on solid YSZ electrolytes with the method of screen printing. The prepared/calcined electrodes were kinetically studied, in the form of half cells, for their catalytic activity for the Reverse Water Gas Shift Reaction in the temperature range of 800-900 oC with simultaneous analysis of products/reactants using gas chromatography. Electrocatalytic measurements with Electrochemical Impedance Spectra (EIS) analysis were also performed in single solid oxide cells, within the same temperature range, under H2O electrolysis conditions by applying different pH2O/pH2ratios. Acknowledgments The research leading to these results has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under the project SElySOs with Grant Agreement No: 671481. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation Programme and Greece, Germany, Czech Republic, France, and Norway.