Scalable and high efficiency materials and reactors for direct solar hydrogen production

Expected Outcome

Facing a period of climate emergency and energy crisis, Europe needs to rethink the energy market with solutions based on renewable sources capable of directly generating renewable fuels. Hydrogen is a valuable energy carrier and an important feedstock for industry, but its production still relies almost exclusively on fossil fuels. The conversion of solar energy into chemicals such as hydrogen is expected to grow in importance as a sustainable energy resource. Especially, thermo-chemical cycles (TCC) or photoelectrochemical/photocatalytic (PEC/PC) water splitting using sunlight represent eco-friendly and promising technologies to produce hydrogen with the possibility to have standalone systems for delocalised production not necessarily connected to the power grid.

To date, thermochemical and photo-assisted solar-driven technologies are still in the proof-of-concept stage and face challenges in improving solar-to-hydrogen conversion efficiency to make solar-based hydrogen production competitive. Additionally, R&D in materials should aim to discover novel abundant and cost-effective catalysts and redox materials as well as more integrated process design promises in the respective fields. Development of TCC or PEC/PC reactors is essential along with overcoming challenges related to the efficiency, stability and scalability.

TCC processes use high-temperature solar heat to drive redox reactions that decompose water into hydrogen and oxygen through a series of chemical steps. These cycles typically involve metal oxides or non-metal oxides or other chemicals that undergo reversible oxidation and reduction, enabling the splitting of water. Although several materials and cycle configurations have demonstrated feasibility at kW scale, the technology remains at an early stage of development, with key challenges related to redox material stability, reaction kinetics, and efficient heat integration. Experimental systems have shown proof-of-concept operation under concentrated solar flux, but current solar-to-hydrogen efficiencies and long-term durability need significant improvement to meet industrial targets.

PEC/PC processes utilise light energy (in some cases in combination with electric energy) to drive chemical reactions, particularly for the production of hydrogen from water. This method is regarded as environmentally friendly and holds promise for generating hydrogen with standalone systems that do not require connection to the power grid. The conversion of solar energy into chemicals such as hydrogen is anticipated to grow in relevance as a sustainable energy resource. For instance, PEC water splitting systems are anticipated to play a significant role in renewable hydrogen production, with the goal of competing in the medium to long term with conventional systems that combine separate photovoltaic (PV) panels and electrolysis units. Innovative PEC technologies can support CAPEX and OPEX reduction efforts compared to electrolyser development and thereby can help boost the market competitiveness of renewable hydrogen.

The results are expected to contribute to all the following outcomes:

• Solar-driven water to hydrogen conversion will be demonstrated in relevant scale and over substantial demonstration periods using innovative reactor concepts;
• New TCC or PEC/PC systems integrating components and materials which require only the unavoidable minimum of critical raw materials (CRM) in order to mitigate CRM dependency of renewable hydrogen production paths through diversifying the technology options;
• Novel TCC or PEC/PC reactor and balance of system designs, based on continuous operation rather than batch or semi-batch prototypes, to maximise process efficiency;
• Multiscale model of TCC or PEC/PC reactor to support reactor design and operations;
• Techno-economic and environmental analysis of the proposed technology;
• Contributing to identifying the most cost-effective and highly performing solar water to hydrogen conversion technologies for demonstration and industrialisation after 2030 to accelerate the readiness of renewable hydrogen for all economy sectors;
• Reinforcing the European scientific & knowledge basis and European technology export potential for solar hydrogen production technologies.

The project will contribute to strengthen European leadership for the efficient hydrogen production and create new business models for hydrogen production based on TCC and PEC/PC technologies.

Project results are expected to contribute to the following objectives and KPIs of the Clean Hydrogen JU SRIA for both routes (TCC and PEC/PC) unless otherwise stated[1] :

• Hydrogen production rate: on-sun operation at relevant scale (250-500 kW for the TCC route and 10 kW min for the PEC/PC route) for at least 1 month operation time (net operation time; outdoor or indoor testing under simulated sunlight) reaching average hydrogen production rates higher than 0.75 kg/m²/y (land area) with a convincing potential of reaching 1.42 kg/m²/y (land area) by 2030[2];
• Reactor efficiency: demonstrated conversion efficiency of Solar radiation to Hydrogen (STH) of more than 10%, considering the higher heating value (HHV) of hydrogen; • For TCC ≥ 20 %
• For PEC ≥ 10 %
• For PC ≥ 10 %

• Less than 10 % decrease per year of the STH extrapolated from the measure performance over 300 hours of cumulated operation under natural or simulated sunlight;
• Hydrogen production costs: • For TCC route • Calculated system capital cost assuming a scaled-up plant reaching 7.4k€/kg/d by 2030[3]
• Calculated operational cost assuming a scaled-up plant reaching 0.3 €/kg by 2030[4]

• For all relevant routes, an overall cost of production of hydrogen of less than 6€/kg H2[5]

For PEC/PC route, conventional systems that combine separate photovoltaic (PV) panels and electrolysis units are excluded from the scope of this topic.

Scope

This topic seeks innovations in solar thermos-chemical cycles (TCC) and solar Photoelectrochemical/Photocatalytic (PEC/PC), with a strong emphasis on system-level integration (subcomponents: materials, devices, reactors, control systems, etc. into a fully functional, operable system), targeting demonstration at TRL 5, and aligning with EU climate neutrality and energy resilience goals. Proposals should focus on the direct conversion of solar energy into hydrogen, eliminating reliance on intermediate photovoltaic-to-electricity pathways.

Past and current projects supported by the Clean Hydrogen Partnership have established the current technological challenges to overcome for direct solar process generating hydrogen[6],[7],[8],[9]. Therefore, the success of all processes under consideration (TCC and PEC/PC) is strongly linked to the performance of the core components and their interaction. Especially high efficiencies and throughput are required to provide a clear economically competitive scaling and implementation perspective. Innovative solutions including the material, reactor and process level shall be revisited and developed to tackle these significant challenges. The main levers to overcome the efficiency challenges are seen in the following areas: application of advantageous active materials, structures and shapes with better material usage, improved photon and heat management, improved transport processes and heat recovery, as well as co-production of further products besides hydrogen (heat, electricity, other chemical products). A further key for a deployment of such a technology is a convincing pathway for the scaling of the technology. As such, proposals should provide and demonstrate a clear scale-up strategy for the receiver/reactors to substantiate the claim for competitive solutions at 250-500 kW scale for the TCC route and at minimum 10 kW for the PEC/PC route, while considering critical materials and other sustainability issues.

Proposals should make use of already available solar resource harvesting techniques that convincingly demonstrate the promise of commercial application. Possible integration with existing grids (transport, energy, materials) is very important to address the potential application of the proposed technology in future steps. In line with this, proposals can consider including hydrogen intermediate- and end-users or prosumers (on site generation/use as a chemical feedstock or fuel) to demonstrate successful business cases, making efficient use of existing infrastructure and technologies.[10],[11],[12],[13]

Proposals should aim to conduct extensive research and development on the core functional materials of the targeted processes, i.e. redox materials for TCC or light-absorbing and catalytic materials for PEC/PC, as well as innovative reactor and balance of system designs, to produce hydrogen directly from water using solar irradiation in non-concentrated, moderately or highly concentrated form.

Another relevant aspect to consider is the operation of the systems under transient solar irradiation conditions, which may require control strategies or thermal storage elements to ensure process stability and efficiency. Such transient conditions not only demand appropriate control strategies or thermal storage elements to ensure process stability and efficiency but also negatively impact on the lifetime of components, e.g. by accelerating materials degradation. Therefore, adapted suitable operational strategies are needed to deal with intermittency of solar radiation.

The topic should cover the following elements:

• Depending on the proposed technology, improvement of catalyst and redox materials (high thermal stability, cyclability, faster kinetics, and higher hydrogen yield), electrodes and photoelectrodes, receivers and membranes for better efficiency and lifetime minimising CRMs;
• Ensure reusability / recovery of materials and components, as much as possible;
• Work on an integrated architecture and reactor design that minimises material use and optimises the balance of plant, with consideration for modular assemblies;
• Strong focus on scalability of process and design;
• Smart energy and heat management within the process as a whole;
• Assessment of efficiency at relevant scale and representative conditions (including dynamic) and verification of minimal efficiency losses upon upscaling;
• Identifying degradation mechanisms across different scales and implementing countermeasures;
• Support through modelling (e.g. development of thermodynamic/electrochemical models to support material developments and/or 3D CFD models for optimised reactor design);
• Full techno-economic and LCA analysis;
• Development of end of life and recycling strategies for functional materials and core components.

Proposals should cover the following elements addressing the described challenges in TCC and PEC/PC processes to advance the technology to achieve at least TRL 5: system performance, reactor development and material development, all supported by a solid business case. This should be validated by developing, building, and testing dedicated reactor units and peripherals to achieve the performance characteristics given in the section Expected Results.

The intended project should consider or even use results and experiences from relevant ongoing or past JU projects such as but not only HYDROSOL-Beyond[14], HySelect[8], FLOWPHOTOCHEM[16] and PH2OTOGEN[11].

Proposals may be developed in accordance with the results of relevant past and ongoing projects funded by the EU, including the HYDROSOL family[18] (HYDROSOL-beyond[14], HYDROSOL-II[20], HYDROSOL-Plant[12]), SOL2HY2[9], PECSYS[23], and PH2OTOGEN[11], among others (e.g. Sun-to-Liquid [25],and NanoPEC[26]) with the objective of ensuring complementarity and clear added value in comparison with the current state-of-the-art.

For additional elements applicable to all topics please refer to section 2.2.3.2.

Activities are expected to start at TRL 3 and achieve TRL 5 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 3.00 million would allow these outcomes to be addressed appropriately.

Technology Readiness Level - Technology readiness level expected from completed projects

Activities are expected to start at TRL 3 and achieve TRL 5 by the end of the project - see General Annex B.

[1] In the currently available version of the Clean Hydrogen JU SRIA, there are KPIs and objectives for the TCC route for hydrogen production but not yet for the PEC/PC routes.

[2] KPI-1: Boundary conditions: location with direct normal irradiation (DNI) of 2500 kWh/m2/year. Output of hydrogen meeting ISO 14687-2 at a pressure of 15 bar and hydrogen purity 5.0.

[3] KPI-2: System capital cost for a specific hydrogen production rate based on kg of hydrogen generated per day at a given cumulative DNI per year. Capital cost should include all the cost related to all the equipment necessary for the normal operation of the plant.

[4] KPI-3: O&M cost averaged over the first 10 years of the system. Routine maintenance and "wear and tear" (rotating parts, cleaning of equipment, etc). Electricity costs for operation of auxiliary units included. System level losses such as heliostat collector area losses, replacement parts, operation, and maintenance are included in the cost calculations.

[5] S. Haussener et al. Energy & Fuels 2024 38 (13), 12058-12077

[6] https://cordis.europa.eu/project/id/303435

[7] https://cordis.europa.eu/project/id/621252

[8] https://cordis.europa.eu/project/id/101101498

[9] https://cordis.europa.eu/project/id/325320

[10] https://cordis.europa.eu/project/id/245224

[11] https://cordis.europa.eu/project/id/101137889

[12] https://cordis.europa.eu/project/id/325361

[13] https://cordis.europa.eu/project/id/621173

[14] https://cordis.europa.eu/project/id/826379

[15] https://cordis.europa.eu/project/id/101101498

[16] https://cordis.europa.eu/project/id/862453

[17] https://cordis.europa.eu/project/id/101137889

[18] HYDROSOL, HYDROSOL-II, HYDROSOL-Plant (FP6–H2020, Grant 826379, 20030, 325361) – Series of projects on solar thermochemical hydrogen production via redox cycles, progressively scaling from lab to pilot plant.

[19] https://cordis.europa.eu/project/id/826379

[20] https://cordis.europa.eu/project/id/20030

[21] https://cordis.europa.eu/project/id/325361

[22] https://cordis.europa.eu/project/id/325320

[23] https://cordis.europa.eu/project/id/735218

[24] https://cordis.europa.eu/project/id/101137889

[25] https://cordis.europa.eu/project/id/654408

[26] https://cordis.europa.eu/project/id/227179