HycycleS aims at the qualification and enhancement of materials and components for key steps of thermochemical cycles for solar or nuclear hydrogen generation. The focus of HycycleS is the decomposition of sulphuric acid which is the central step of the sulphur based family of those processes, especially the hybrid sulphur cycle and the sulphur-iodine cycle. Breakthrough developments are targeted for both with an accent on the hybrid sulphur cycle. Emphasis is put on materials and components for sulphuric acid evaporation, decomposition, and sulphur dioxide separation. The suitability of materials and the reliability of the components will be shown in practice by decomposing sulphuric acid and separating its decomposition products in scalable prototypes. The final aim is to bring thermochemical water splitting closer to realisation by improving the efficiency, stability, practicability, and costs of the key components involved and by elaborating detailed engineering solutions. The activities comprise the experimental identification and evaluation of suitable materials – in particular ceramics of the SiC family, development and test of the key components evaporator, decomposer, and separator as prototypes, qualification of catalysts, construction materials and components, modelling of those components and characteristics of materials, and analysis of the techno-economic impact on the overall process. The project takes into account the activities currently performed in the US, Japan, and Australia. Therefore key partners from those countries, Westinghouse, JAEA, and CSIRO, are involved to ensure coordination of activities and information exchange with respect to sulphur based cycles in the different continents and the definition of interfaces. Beyond that, HycycleS activities will be strongly linked with international initiatives on hydrogen production under the aegis of IPHE, IEA, INERI, and Gen IV to ensure mutual benefit from different international programmes.