SOEC has a huge potential as an enabling technology to facilitate the transition of the global energy system to a sustainable one. The technology offers unrivalled efficiency in hydrogen generation and has a potential to reach low cost. Generation of hydrogen is the first step in realizing a range of P2X-schemes for providing green fuels (e.g. methanol, ammonia or jet fuel) for the transport sector [1,2].

The largest SOEC units manufactured/operated today are in the range of ~1 MW. However, numerous scale up projects are under way and industrial stakeholders are these years investing massively to bring up production capacity.  

In this paper we shall discuss some of the challenges in upscaling SOECs and address some materials issues/opportunities for improving SOEC performance with view to large scale deployment.

The brittle nature of the ceramics used in the cells limits the size of the cells to edge lengths in the range of 10-15 cm. Ideally this should be larger, however, this requires care in the manufacturing, and a tough and strong backbone in the cell. Many stakeholders rely on zirconia to provide the structural backbone of the cell. Transformable metastable tetragonal with  2 – 3.5 mol.% Y₂O₃ substitution is advantageous over fully stabilized cubic version with ~8 mol. % Y₂O₃, as the former has higher strength and toughness. We shall present recent results on optimizing composition and processing routes to maximize toughness and strength, whilst preventing unintended spontaneous transformation to the monoclinic phase during use.

In SOEC one does not need any PGM-materials. However, typically the state of the art cells relies on use of several critical raw materials. Several LREE/HREE materials are used (Ce, Gd, Y, La) and also some critical transition metals like Co/Mn and Ni. For large-scale deployment, it is obviously an advantage if the use of these Critical Raw Materials can be minimized. Introducing performance improvements in terms of production capacity per m² of cell or kg of material is an important strategy to reduce the CRM-use and is likely a part of the strategy among most stakeholders.

We shall here present recent results on activities to increase the competitiveness of the SOEC technology by introducing a metal-support as the structural backbone and replace the Ni/YSZ-fuel electrode with one based on a mixed conducting Ti-based oxide (Ni and Fe-doped (La,Sr)TiO₃). Recently, we have found that such a material combination can sustain SOEC operation for extended periods (tested over 5000 hr) at current densities exceeding 0.5 A/cm². These durability results shall be presented as shall be findings on the fundamental charge transport properties of the titanates.  

Finally, results of endeavors to improve electrode performance of both fuel and oxygen electrodes will be discussed. On the fuel electrode side, opportunities and challenges of using Ni/CGO in thin electrolyte cells will be addressed and on the oxygen electrode side, results on boosting of performance via various infiltrates will be summarized.