Selection of Highlights of the European Project Next Generation Solid Oxide Fuel Cell and Electrolysis Technology – NewSOC

Abstract

Solid oxide technologies (SOC: Solid oxide fuel cells SOFC & Solid oxide electrolysis SOE) are key enabling technologies for energy systems based on renewable sources and allow for a strong interlinking of sectors electricity, heat, and gas/fuels. SOC can emerge as key players in many concepts, such as fuel/gas to power and heat at small to large scale, energy storage through power to hydrogen/fuel, utilization and upgrading of biogas, balancing of intermittent electricity from renewable sources through load following and reversible operation, and central and decentral solutions for electricity and heat production. In a time, where first SOC systems enter demonstration and commercial markets, the NewSOC project focusses on next generations. It aims at significantly improving performance, durability, and cost competitiveness of solid oxide cells & stacks compared to state-of-the-art (SoA). In order to achieve these goals, NewSOC investigates twelve innovative concepts in the following areas: (i) structural optimization and innovative architectures based on SoA materials, (ii) alternative materials, which allow for overcoming inherent challenges of SoA, (iii) innovative manufacturing to reduce critical raw materials and reduction of environmental footprint at improved performance & lifetime. The NewSOC unifies competences of 16 strong research and industry players. First scientific highlights were achieved despite the challenging working conditions under the European wide covid-19 restrictions in the first year of the project. The presentation will provide a selection of these highlights. One focus area is the development of novel electrode materials, where high performance, impurity tolerance and stability are the primary targets. Nanostructured fuel electrodes based on doped SrTiO3 perovskites such as LaSrFeNiTiO3 are being developed as backbones. Subsequent, wet infiltration of Ni:GDC ensures high electro catalytic activity and ionic conductivity, while retaining the advantages of Ni-metal free fuel electrodes outlined above. Furthermore, a class of doped lanthanum chromites (La0.75Sr0.25CrxM1-xO3-δ, M=Fe, Mn, Ni) is developed as Ni-metal free fuel electrodes, to overcome the challenges faced by the SoA Ni-cermets. The perovskite structured electrodes, combined with highly conductive electrolytes have high performance, low ASR and flexibility in various operating modes (SOEC, rSOC). The most attractive feature of this class of electro catalysts is that they retain their properties (oxidative state, conductivity) in reducing and oxidizing environments at SOC operating temperatures, even in absence of a reducing agent, i.e. H2. Another approach is to modify SoA electrodes. Commercial (SoA) Ni/GDC was modified with iron by deposition – precipitation (D.P.), leading to enhanced performance as functional SOE fuel electrode. The promoting effect depends on the wt.% Fe content, where D.P. of quite a small amount of iron, through the formation of a Ni-Fe alloy, caused a 3-fold enhancement compared to Ni/GDC. Interestingly, the 0.5-Fe-Ni/GDC electrode performed similarly well like the noble-metal modified 3Au-0.3Mo-Ni/GDC. Materials compositions and structuring go hand in hand for tailoring cell properties. Under this focus, novel air electrode architectures for SOFC & SOE applications based on Co- and Ni-free materials with the (La, Ca, Sr)FeO3 perovskite class of materials are developed. The typically increased overpotential of Co- and Ni-free air electrodes is a challenge, which is tackled by introduction of a patterned porous barrier layer and addition of a composite layer at the electrode/electrolyte interface to enhance the triple phase boundary density between electrolyte and the Co-free air electrode. In another approach, the microstructure of SoA Ni/YSZ and LSCF/GDC electrodes was assessed to identify the best tradeoff between the cell performances, the durability and the robustness by a methodology coupling of manufacturing, characterization, and modeling. As a result, the performance of the LSCF/GDC composite electrode was improved, with different porosities, graded electrodes and composites. The role of the Ni/YSZ microstructure on the Ni migration during operation was investigated, with focus on finer and more homogeneous electrodes. Manufacturing and deposition methods contribute significantly to performance & lifetime, but also costs and environmental impact of SOC production. Thus, alternative approaches providing cells & stacks with required specifications are part of the NewSOC project. Progress on sputter deposited GDC buffer layers has been obtained in view of their implementation in the fabrication process of commercial Solid Oxide Fuel Cells.