Development and validation of pressurised high temperature steam electrolysis stacks (Solid Oxide Electrolysis)

Solid Oxide Electrolysis (SOEL) operating at 650-850°C, can be improved with pressurised operation. The integration of SOE stacks with balance of plant components proved the successful use of these systems at now significant scale (> 700 kW) and the road is paved towards MW scale thanks to a modular approach simplifying the scale-up step. However, these systems are designed for operating efficiently and durably at atmospheric pressure. There have been previous FCH JU projects[[https://www.clean-hydrogen.europa.eu/projects-repository_en]] dedicated to pressurised High-Temperature Steam Electrolysis (HTSE) at small scale for SOE. Pressurised operation has been validated up to 30 bar at cell scale, and up to 15 bar at stack scale embedded in a pressure vessel[[SOPHIA and HELMETH projects: https://www.clean-hydrogen.europa.eu/projects-repository_en]]. These previous activities highlighted the need for more research efforts directed to the optimisation of components, cells and stacks to improve current density and stability in pressurised operation for SOEL technologies. Furthermore, additional efforts should focus on system integration and on defining optimal boundary operations for dedicated user cases in order to maximise the efficiency of the integrated scenarios (e.g. taking into account thermal integration and possible side stream products). This opens for the development of novel and/or improved systems concepts, where the benefits of pressurised electrolysis should be leveraged for deployment in large-scale centralised systems with economies of scale, hydrogen distribution to end uses, as well as distributed systems located at demand centres.

Proposals for this topic should set out a credible pathway to contribute to the development and validation of pressurised SOEL with technological breakthroughs aiming at designing and operating a stack at an optimal pressure with eventual assistance of a downstream compression process to reach higher delivery pressure. Electrochemical compression in the stack can also be considered. To tackle these challenges, the proposals should focus on system and stack design, as well as fabrication, assembly and testing of stack in the conditions suitable for the relevant business cases as follows:

• System design should be defined based on optimal integration of SOEL in selected application(s) taking into account the operating limits of the SOEL. This activity will entail defining the optimal operating pressure of the stack and system to balance electricity consumption and heat demand at nominal capacity;
• A techno-economic evaluation of the SOEL integrated in given application(s) will provide Levelised Cost of Hydrogen (LCOH) of the pressurised SOEL system taking into account economy of scale and will be used to evaluate the impacts of the various modes of operation (e.g. atmospheric SOEL + pressurisation afterwards, pressurised SOEL, and combination of modes). Comparing the technology with e.g. other alkaline and PEM electrolysers, operating in pressurised mode using similar boundary limits will also provide insights into relevant business models. The proposals will furthermore aim at reaching the capital costs below 2,000 €/(kg/d). The project should also compare the efficiency gains between pressurised electrolyser and unpressurised with compressor for various system sizes;
• Stack designed for high current density (SOEL: 0.85 A/cm²) should be successfully operated over one long term test of at least 2,000 hours and 4,000 hours of aggregated testing time in relevant pressurised operating conditions at a minimum of 5 bar and conforming to the envisaged use case;
• Degradation mechanisms and boundary operation of the stack and its components should be identified with respect to pressure, temperature, load, in stationary and transient conditions;
• Modelling should be used to support the development of cells and/or stacks.
• The stack(s) should be tested at scale of minimum 10 kW; the considered pressure will be selected in relation to the targeted use case (s) to minimise energy loss;
• The stack should be operated in representative conditions to evaluate its, as well as its durability during a 2,000 hours long term test. This should include some pressurisation/depressurisation cycles;
• The applicants should provide thorough analysis of safety aspects, such as safety shut-off, and focus on establishing smooth operation modes including pressurisation and depressurisation.

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

Proposals are expected to address sustainability and circularity aspects.

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 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.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2022 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2021–2022 which apply mutatis mutandis.