Specific R&I areas are needed to be tackled to further progress PEC and PC before demonstration in an industrially relevant environment as follows:

• Demonstration of a commercially viable PEC or PC devices, i.e. comprising a single component that integrates both the solar harvesting and catalytic function. Therefore, proposals on PV biased electrolysis or PV biased PEC devices are not in the scope of this topic;
• Novel photo-chemical reactor design, based on flow conditions rather than batch or semi-batch prototypes;
• Integration of solar concentration architectures, featuring photon management concepts through suitable optics and heat removal and usage concepts, or via disruptive nanomaterials design that promote local concentration of the incoming radiation;
• Expansion of the arsenal of materials for efficient solar energy conversion, including semiconductor oxides, selenides, nitrides, halide perovskites, polymers and the respective hybrids, as well as bio-hybrids enzyme-semiconductors, also leveraging on Z-schemes or multi-junction semiconductor systems. Approaches promoting the use of abundant or easily recoverable materials is encouraged;
• Development of effective passivation strategies to mitigate chemical/electrochemical corrosion of semiconductor photoelectrodes and photocatalysts and thereby improve their operational lifetime;
• Development of cost-effective, scalable processing methods enabling the coupling of efficient hydrogen evolution, oxygen evolution or electro-oxidation (co)catalysts to semiconductor photoelectrodes and photocatalysts;
• Alternative photo-chemical reactions beyond conventional water splitting, de-coupling hydrogen and oxygen production in favour of more economically attractive and/or less energy-demanding oxidative reactions, such as biomass/waste photo-reforming or direct saltwater photo(electro)catalysis.

Proposals should address the following targets at the system level:

• A photo(electro)chemical system with a minimum cumulated hydrogen production of 75 kWh/m2 for PEC or 25 kWh/m2 for PC systems, respectively, for the 500 hours of pilot demonstration;
• The concepts used in developing the novel reactor should allow scalability to higher throughput not only by numbering up reactors but also by increasing the single reactor throughput;
• Photo(electro)chemical reactions beyond conventional water splitting may be also demonstrated, in particular hydrogen-producing de-coupled reactions improving state-of-the art demonstration of solar-to-chemical energy conversion;
• A functioning prototype of the system should be validated in a relevant environment, in particular by using natural sunlight.