The FreeHydroCells project aims to create a new photoelectrochemical (PEC) system capable of clean, efficient solar-to-chemical energy conversion, with hydrogen gas storing the chemical energy. The system would mimic, to some extent, the solar-energy absorption potential of a leaf but by using thin semiconducting materials as buried pn-junctions that, when submerged in water and exposed to sunlight, are capable of freestanding PEC water splitting. A large number of technological challenges restrict the cost-effectiveness, efficiency and realisation of clean, green, solar-to-chemical hydrogen, state-of-the-art systems, making it commercially unattractive, and severely limiting green hydrogen’s role in decarbonisation. However, the FreeHydroCells project proposes to leverage a number of ideas connected to advancements in thin film materials, devices, and processes to try to make progress in this area.
The main objectives of the project are: to develop new component TCO and TMD materials and a suitable TCO/substrate, integrate them via aligned processes into a buried multijunction integrated tandem PEC cell, and develop and optimise the created PEC cell from small area proof of concept to large area proof of concept and using commercially-compatible deposition tools of ALD or CVD. The aim is to eventually achieve unassisted water splitting with the PEC cells. The project also aims to take the novel developed PEC cell and use it within an innovative PEC system once the PEC cell-to-system challenges are overcome, which to date provide a bottleneck for the state-of-the-art (SOA) to develop a viable system.
The issues preventing unassisted water splitting are many, including the issues preventing a sufficient solar-to-hydrogen efficiency versus cost (both in terms of production and operational financial and energy input costs). Sustainability and long service life are also critical factors for cost-effective uptake and supply continuity versus other, typically cheaper, fossil fuel energy sources. Sustainability means we must use environmentally-benign elements to achieve our objectives, and a long service life means we must achieve both cell and system stability, durability and reliability. These issues are especially problematic at the PEC system level, and to date, the SOA has not achieved an affordable and viable efficiency/cost ratio for PEC water splitting hydrogen production. The project is considered by the EU as a high-risk/high-reward research and innovation action, emphasising the likelihood of very limited success due to the significant bottleneck issues that remain after 50 years of research in this area.
