(Digital Presentation) Au-Mo-Fe-Ni/CeO2(Gd2O3) As Potential Fuel Electrodes for Internal CO2 Reforming of CH4 in Single SOFCs
Authors: Ioannidou Evangelia , Neophytides Stylianos G. , Niakolas Dimitris K. 
Published: September 2023

Recycling biogas to produce syngas (H2 + CO) through Dry Reforming of Methane (DRM) has currently attract resurgent interest. Biogas consists mainly of CH4 (55-65%) and CO2 (35-45%) and is widely produced by anaerobic fermentation of biomass [1]. DRM provides a feasible solution to eliminate greenhouse gases via production of useful chemicals and hydrocarbons.

Considering the DRM energy applications the produced syngas can be used as a fuel in high temperature solid oxide fuel cells (SOFCs) for electricity production or biogas can be directly fueled in the cell without the need of an external reformer (Internal Dry Reforming of Methane, IDRM), which simplifies the SOFC system and reduces the cost [2,3]. Specifically, during IDRM at temperatures higher than 800 oC, the catalytic Reverse Water Gas Shift (RWGS) reaction may run in parallel with electrocatalytic reactions, resulting in the consumption of valuable H2. In addition, carbon deposition on the electrocatalyst surface due to CH4 decomposition, which is favored at elevated temperatures (≥ 700 oC), may also occur resulting in progressive electrocatalyst deactivation [4].

Ni-based ceramic-metal composites with Yttria Stabilized Zirconia (YSZ) and Gadolinia Doped Ceria (GDC) are widely used as electrocatalysts in SOFCs because of their activity and inexpensiveness. However, nickel catalyses the formation of carbon deposits from hydrocarbons and exhibits a tendency to agglomerate after prolonged operation [3,4]. The carbon tolerance and anti-sintering tendency of nickel and specifically of Ni/GDC can be enhanced, by dispersing trace amounts of transition noble (Rh, Pt, Pd, Ru, Au) or non-noble (Co, Cu, Mo, Fe) metal elements [3,5].

In this study the catalytic and electro-catalytic performance, as well as the coking resistance of Au (1 and 3 wt.%), Mo (0.4 wt.%) and Fe (0.5 and 2 wt.%) modified Ni/CeO2(Gd2O3) electro-catalysts were studied as half and full electrolyte supported cells under internal CO2 reforming of CH4 in single SOFCs, at 750-900 oC. The aim was to elucidate their activity towards the consumption of CH4, CO2, the production of H2, H2O, CO and the production of carbon, as a function of temperature and the applied current density under a biogas fuel mixture of CH4/CO2=1. Additionally, the cells comprising a modified Ni/GDC fuel electrode, an 8 mol% Y2O3 stabilized ZrO2 (8YSZ) electrolyte were characterized using I-V measurements and Electrochemical Impedance Spectra (EIS) analysis in order to investigate the evolution of the ohmic and polarization resistance values as a reflection of current. Complementary physicochemical characterization includes thermo-gravimetric measurements for the catalytic dissociation of CH4 and CO2 at 800 oC. In brief, the cell with Ni/GDC was more active catalytically compared to the modified cells, but exhibited worst electrocatalytic performance. The cells with 3 wt.% Au-0.4 wt.% Mo-Ni/GDC and 3 wt.% Au-0.5 wt.% Fe-Ni/GDC fuel electrodes were moderately active catalytically, but performed better. The main degradation factor for the unmodified cell was the higher carbon formation, which increased gradually with the increased current and was reflected on higher ohmic and polarization resistance values compared to the modified cells.

Acknowledgments

This research has been co-financed by the European Union and Greek national funds through the operational program ‘Regional Excellence’ and the operational program ‘Competitiveness, Entrepreneurship and Innovation’, under the call “RESEARCH-CREATE-INNOVATE” (Project code: T2EΔK-00955).

References

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[5] Niakolas, D.K., Neofytidis, Ch., Neophytides, S.G. (2017). Frontiers in Environ. Science. 5: 78.