As Europe accelerates its transition to clean energy, the Net Zero Industry Act identifies low-carbon hydrogen production as a strategic priority. DELYCIOUS tackles key challenges in water electrolysis technology, focusing on extending electrolyser lifespans and reducing operational costs under variable renewable energy sources. The project pioneers innovative approaches by integrating Raman and Electrochemical Impedance spectroscopies with advanced physical and data-driven modelling. These tools will be validated across three major electrolysis technologies: alkaline (AEL), proton exchange membrane (PEMEL), and solid oxide electrolysis (SOEL), with a demonstration on alkaline electrolysers beyond 100 KW.