Development of low temperature water electrolysers for highly pressurised hydrogen production High-pressure electrolysers should be compatible with direct injection into chemical industry and gas networks both onshore and offshore as the avoidance of mechanical compressors are of crucial importance to reduce the LCOH and improve the availability of systems. The developed electrolysers may reach low LCOH for both centralised and decentralised applications due to the unique modular approach.The scope of this project is to develop the next generation of water electrolysers (PEMEL or AEMEL) operating below 150 ºC for pressurised hydrogen production at the pressure of minimum 50 bar for AEL and AEMEL and 80 bar for PEMEL further advancing innovations developed in projects[[https://www.clean-hydrogen.europa.eu/projects-repository_en]] like NEPTUNE and PRETZEL.To this extent, breakthroughs in materials science of cell components should encompass advances in the cell design, cell architecture and BoP modules. This requires a completely new design enabling: low energy consumption and low degradation rates while contributing to reduce the hydrogen production costs.Novel stack concepts should be designed, whilst innovations in BoP (e.g. integration of innovative compression solutions with electrolyser stacks), advanced materials with longer term durability and components (membranes/diaphragms, porous transport layers, bipolar plates, catalysts) developed and integrated into a short-stack prototype.Targeted prototype scale and cell size should be appropriate for targeted application but a scale of minimum 50 kW for AEL and PEMEL and 25 kW for AEMEL, including larger cell areas than SoA, should be addressed.Proposals should demonstrate how the concepts developed will be validated in a laboratory (TRL4) but should also include testing in relevant environment (TRL5) to pave the way for end-use applications (e.g. technology could be tested for injection in transmission natural gas grid). This includes the validation at the single cell and stack levels, testing the components at nominal, steady state and dynamic conditions and identifying a best candidate solution.Operations at elevated pressures should be validated under various operating conditions (understood as directly scalable to multi-MW electrolysers) in order to develop new control strategies and to optimise operation at high-pressure and evaluate the effect of pressure in the case of hot starts and cold starts.Proposals should investigate the high-pressure effects on the overall electrolysis process, both with respect to the effect of increased gas solubility, bubble-formation and the effect on electrode overpotentials and ohmic losses as well as the associated increase in gas cross-over at elevated pressures.Optimal stack and cell design in terms of structure and geometry (e.g. spacing distances within the cell) should be within the scope of proposals.Research on corrosion effects on the cells and/or lifetime prediction model and mitigation strategies should be conducted in order to maintain lifetime and degradation.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 126.96.36.199 ""Collaboration with JRC""), in order to support EU-wide harmonisation. Test activities should adopt the already published EU harmonised testing protocols[[https://www.clean-hydrogen.europa.eu/knowledge-management/collaboration-jrc-0_en]] to benchmark performance and quantify progress at programme level.Activities are expected to start at TRL 2 and achieve TRL 5 by the end of the project. The conditions related to this topic are provided in the chapter 188.8.131.52 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.