Solar Energy for Carbon-Free Liquid Fuel

Project Information

Sun-To-X

Grant agreement ID: 883264

DOI

10.3030/883264

Project closed

EC signature date 7 April 2020

Start date 1 September 2020

End date 29 February 2024

Funded under

• SOCIETAL CHALLENGES - Secure, clean and efficient energy

Total cost

€ 3 096 643,75

EU contribution

€ 2 999 143,75

Coordinated by

TOYOTA MOTOR EUROPE NV
Belgium

Periodic Reporting for period 3 - Sun-To-X (Solar Energy for Carbon-Free Liquid Fuel)

Reporting period: 2023-03-01 to 2024-02-29

Summary of the context and overall objectives of the project

Currently around 80% of the energy we use comes from chemical fuels, such as gasoline. Although renewable energy sources are increasingly used for electricity generation, the production of chemical fuels has proven more challenging. However, we urgently need to address this problem to achieve the goals set by the European Commission to be carbon neutral by 2050. The Sun-To-X project aims to develop technology for the production of chemical fuels derived from solar energy. In the first step of our process, we will use solar energy to produce hydrogen from water (from ambient humidity or rain) through a photoelectrochemical device. In the second step, the hydrogen will be reacted with a silicon oxide precursor to form HydroSil - a energy dense, non-toxic, liquid fuel, which can utilise existing infrastructure for its transport to consumers. When used in combination with a fuel cell, Hydrosil produces only water as an output, along with the silicon oxide starting material which can be recharged with hydrogen. In the scope of the project, we will also explore another use for Hydrosil in the recycling of waste plastics. The Si-H bonds in Hydrosil can react with plastics to form hydrocarbon materials.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Solar Hydrogen Production:
A transparent conducting porous substrate based on fluorine-doped tin oxide coated quartz felt has been developed as a photoelectrode support - this substrate allows gas (humidity) to enter the photoelectrode whilst allowing light to pass through the photoanode (an inorganic oxide, on top of the device - absorbing blue light) to photocathode (an organic, conducting polymer, absorbing red light). For the photoanode, has been selected. Techniques to deposit these semiconductors (along with the necessary charge transport layers, co-catalysts, passivation layers and proton-conducting, water absorption layers) on to porous substrates have been developed and scaled up to allow the production of photoelectrode at a greater than 100 cm2 scale. The 100 cm2 photoelectrodes have been assembled into membrane photoelectrode assemblies in 9 modules to construct the photoelectrochemical device of around 900 cm2 active area.

Silicon Hydrides and their Use for Recyling of Plastics:
The different reaction steps for storing hydrogen in HydroSil and the connection between them have been validated and a reactor has been designed that provides heat via solar thermal energy. Techniques to characterise the silicon hydride materials have also been developed. Catalysts have been tested to enhance the reaction of the Si-H bonds in HydroSil for the breakdown of waste plastics such as polycaprolactone (PCL). With an optimised catalyst, more than 95% conversion of waste plastics to hydrocarbon materials such as 1,6 hexanediol has been achieved. Furthermore, the reactions have been demonstrated to be selective allowing effective recycling of plastic mixtures.

Exploitation and Dissemination
Throughout the project, the Sun-To-X consortium has engaged with stakeholders through attendance of workshops and conferences (23 presentations), publications (seven in peer-reviewed journals (with further articles under review / preparation), one conference proceeding and one general article) and social media. Particularly the transparent photoelectrode support has generated a lot of interest and was reported by more than 60 media outlets following the scientific publication. 12 key results have been identified over the project scope in the exploitation plan of the project with one patented and one patent under consideration.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Mitigating climate change and enhancing energy security
We have demonstrated a proof of concept tandem device for photoelectrochemical hydrogen production from ambient humidity, developed a charging process to store this hydrogen in HydroSil, a novel silicon hydride based liquid fuel to facilitate hydrogen transportation and storage, and the use of HydroSil in the production of hydrocarbon fuels. The technologies developed in this project have reached TRL 4, so further development is required to reach maturity. However, the solar-driven nature of Sun-To-X processes could reduce our future dependence on CO2-emitting fossil fuels not only through energy generation but also in energy storage. Facile storage of energy is critical for Europe where there is a large seasonal variation in renewable energy supply e.g. sunlight hours, the storable nature of HydroSil allows a continuous energy supply over the year.

Use of abundant resources to expand global applicability of our technology
During the project we focused on sustainability not only on the use of renewable energies e.g. solar, but on the materials and feedstocks for the processes we investigated. Our solar hydrogen system uses water vapour as a feedstock, expanding the range of geographical locations that our technology can be applicable i.e. the areas with highest solar irradiation tend to have a limited freshwater supply. Furthermore, HydroSil uses silica as a basis for the hydrogen storage process, that is readily available globally. Finally, we have also investigated the use of HydroSil in waste plastic recycling, turning plastic waste into useful fuels and chemicals towards a more circular economy.

Contribution to European innovation in sustainable energies
Sun-To-X combined expertise from academia, SMEs and the industrial sector, allowing a range of innovation between fundamental research and device development. Over the course of the project we have published nine articles in scientific journals related to sustainable fuels and chemicals (cited over 100 times as of April 2024) with further publications planned based on our most recent results. One patent has been filed on a transparent gas diffusion layer, that enabled the production of the tandem, vapour-fed device.

Collaboration with Mission Innovation
The Sun-To-X project has also engaged with Mission Innovation, an international organisation that aims to advance research globally on sustainable energy through collaboration. We have organized two public events together with them to explain the results and impact of Sun-To-X and other Mission Innovation projects.

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