Large scale sustainable hydrogen production is necessary to implement hydrogen as an energy vector in a future decarbonised economy. High temperature electrolysers based on solid oxide cells, so-called SOEL, offer the highest electrical efficiency among competing electrolyser technologies, but their capital expenditure (CAPEX) and degradation rates remain higher than AEL and PEMEL. In addition, their capability to operate under dynamic conditions of variable load and rapid start up, as required for direct coupling with renewable and intermittent energy sources, is more limited due to the brittleness and thermal inertia of ceramic components.

The outcome of this topic will be an innovative low-cost and compact cell and stack concept that can be operated at intermediate temperatures (up to<700^oC), enabling dynamic operations (i.e. variable load and rapid start and stop) and longer lifetime for energy efficient hydrogen production, therefore contributing to the overall objectives of the Clean Hydrogen JU SRIA to reduce hydrogen production cost to 3 €/kg by 2030.

Project results are expected to contribute to all the following expected outcomes:

• Cells and stacks produced by scalable manufacturing techniques with potential for later integration and automation into a pilot line;
• Cells and stacks designed for flexible operation at intermediate temperatures (550- 700°C) and variable load and rapid start and stop (for coupling with renewable energy sources);
• Renewable hydrogen production with direct coupling of renewable energy sources potentially benefiting from thermal integration and reducing CO₂ footprint;
• European leadership for renewable hydrogen production based on SOEL electrolysers;
• Strengthened European value chain on electrolyser components with decreased reliability of critical raw materials from international imports;

Project results are expected to contribute to the following objectives and KPIs of the Clean Hydrogen JU SRIA:

• Demonstrate successful start-up of the stack with a hot idle ramp time of 240 second and cold start ramp time of 6 hours;
• Increase current density of cells to 1.2 A/cm² for SOEL;
• Demonstrate a degradation rate of 0.75%/1000hr at current density of 1.2A//cm²;
• Establish a roadmap for defining technological pathways enabling to reach: CAPEX ~ 520 €/(kg/d) and operational expenditure (OPEX) of 45 €/(kg/d)/y, values given in SRIA for 2030;

The topic focuses on the development of new cell and stack designs, aiming at the replacement of costly ceramic-based components and reduction of critical raw materials (e.g. light and heavy rare earth materials, LREE and HREE)^[1], and use of lower cost steels. Improved thermal and load cycling capabilities (faster and higher number of thermal cycles) should be ensured by designing new cells and/or stacks based on e.g. metal supported cells/stacks, cells with integrated interconnect/current collector/electrode and/or metal-based monolith cells/stacks and/or intrinsically more robust cell/stack design/assembly. The stack volume should be reduced compared to state-of-the-art stacks, by 15%. This can be sought by nano-engineering and/or self-assembly of interfaces, integrating several functionalities in single components and/or by developing thinner layers that can also contribute to reduce ohmic losses.

The new sustainable-by-design electrolysers will operate at temperature below 700°C to minimise thermally induced degradation and facilitate direct coupling with renewable sources (heat and steam) from e.g., geothermal plants or solar power plants, with efficient thermal management.

Proposals should address the following:

• Design of new cells and/or stacks based on e.g. metal supported cells/stacks, cells with integrated interconnect/current collector/electrode and/or metal-based monolith cells/stacks and/or intrinsically more robust cell/stack design/assembly, and validation in short stack; any results coming out from the SRC projects (e.g. HORIZON-JTI-CLEANH2-2022-07-01: ‘Addressing the sustainability and criticality of electrolyser and fuel cell materials’) which could be relevant for this topic should be considered;
• The short stack based on 5 cells with an active area of minimum 25 cm² per cell should be operated under representative conditions of the targeted application(s) to evaluate its performance and durability over minimum 1000 hours of continuous testing and 2000 hours of accumulated testing;
• Effect of rapid thermal cycling and load cycling on voltage degradation should be investigated. The testing should be in line with protocols set-up by the JRC;
• Fluid dynamics and multi-physics modelling should be used to determine the optimal cell and stack architectures considering thermal management within the stack and optimising its compactness;
• Increased current density of the cells should be obtained by e.g., designing thinner electrolytes and/or new electrodes with improved materials/architectures;
• Corrosion stability of the metal-based components should be validated in relevant operating conditions, in particular for the steam side of the electrolyser, and if needed, improved by development of protective coatings;
• Degradation mechanisms of the cell/stack components should be identified with respect to temperature and load including in dynamic conditions, ripples and transients;
• The cell and stack manufacturing methods should be based on processes that have the potential to be scaled-up, automatised and mass-manufactured at a later stage;
• Techno-economic evaluation of the steam electrolyser integrated in given application(s) and considering economy of scale will provide the Levelised Cost of Hydrogen (LCOH) and will be used to provide insights into relevant business models. The CAPEX of the novel stack concept should be compared to state-of-the-art SOEL stacks as well as other electrolyser technologies such as PEM and alkaline.

Proposals are expected to address sustainability aspects by reducing the use of critical raw materials compared to state-of-art cells and/or stacks and/or their recycling.

Consortia are expected to build on the expertise from the EU research and industrial community to ensure broad impact by addressing several of the aforementioned items.

Proposals should demonstrate how they go beyond the ambition of previous EU supported projects such as METSAPP^[2], METSOFC^[3], RAMSES^[4] and NEWSOC^[5] and be complementary to them.

Proposals are expected to collaborate and explore synergies with the projects supported under topics HORIZON-JTI-CLEANH2-2023 -07-02: ‘Increasing the lifetime of electrolyser stacks’ and HORIZON-JTI-CLEANH2-2022-07-01: ‘Addressing the sustainability and criticality of electrolyser and fuel cell materials’.

Activities developing test protocols and procedures for the performance and durability assessment of electrolysers and fuel cell components proposals should foresee a collaboration mechanism with JRC (see section 2.2.4.3 "Collaboration with JRC"), in order to support EU-wide harmonisation. Test activities should adopt the already published EU harmonised testing protocols^[6] to benchmark performance and quantify progress at programme level.

Activities are expected to start at TRL 2 and achieve TRL 4 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 3.00 million would allow these outcomes to be addressed appropriately

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2023 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2023–2024 which apply mutatis mutandis.

[1] https://www.crmalliance.eu/hrees

[2] https://cordis.europa.eu/project/id/278257

[3] https://cordis.europa.eu/project/id/211940

[4] https://cordis.europa.eu/project/id/256768

[5] https://cordis.europa.eu/project/id/874577

[6] https://www.clean-hydrogen.europa.eu/knowledge-management/collaboration-jrc-0_en