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« Artificial photosynthesis » team of scientists wins Royal Society of Chemistry's Horizon Prize

An international collaboration has been awarded a prize by the Royal Society of Chemistry for a device producing fuels from water, CO2 and sunlight. Interview with Martin Foldyna, CNRS physicist at Laboratory of Physics of Interfaces and Thin Films and member of the team.

Principle of the device demonstrated in "Low-cost high-efficiency system for solar-driven conversion of CO2 to hydrocarbons" Tran Ngoc Huan et al,

With colleagues across the world, you have received the 2021 Environment, Sustainability and Energy Division Horizon Prize from the Royal Society of Chemistry for a device performing “artificial photosynthesis”. Can you explain what it is?

Martin Foldyna : Photosynthesis is the process by which plants, or other living organisms, convert the energy emitted from the sun into chemical energy. For instance, plants can reduce carbon dioxide (CO2) into sugar that act as a fuel. The idea behind artificial photosynthesis is to mimic this process to produce hydrogen and high value-added chemicals like hydrocarbons out of CO2, water and solar energy. Such “solar fuels” could then be used for other processes and may be part of the solution for a more sustainable energy consumption. Artificial photosynthesis is not new, but in our work published in 2019 in PNAS, we demonstrated an efficient, low cost system.

How does it work?

Martin Foldyna : Our device comprises two parts: a photovoltaic cell and an electrochemical one. In the lab, we shine light from a solar illuminator, similar to that emitted by the sun, onto the photovoltaic module that convert it into electrical energy, providing current and voltage. These current and voltage power the electrochemical cell which is dipped into CO2-enriched water. This cell comprises two electrodes made of copper-oxyde acting as a catalyst for the chemical reactions. These reactions decompose water into oxygen and hydrogen, but also produce gaseous carbon-based fuels such as ethane or ethylene. Summed up in this way, it sounds easy. But this involves complicated chemistry. And whereas producing hydrogen is relatively easy, the overall solar-to-hydrocarbon efficiency reached 2.3 %, which is already a very good benchmark.

What were the challenges the team had to overcome?

Martin Foldyna : This is a truly international collaboration. The aim consisted in making a full, efficient system at low cost, because it is key to consider future practical applications. Chemists at College de France have developed an original catalyst for both electrodes: a dendritic nanostructured copper oxyde material. Copper is more abundant and cheaper than other catalyst materials like iridium. Moreover, the dendritic structure means a very high surface for the electrodes, which is beneficial to the reactions. The photovoltaic cells have been fabricated at Politecnico di Torino in Italy.  They are made of perovskite, a family of material with interesting properties for solar applications at low cost. At the Laboratory of Physics of Interfaces and Thin Films (LPICM*), I was involved in integrating the two systems together, making it work and measuring its performance under the standardized solar illumination. In particular, we had to connect multiple photovoltaic cells into a single module, which was challenging because perovskites are fragile and their performance can change over the time. In the end, I think the fact that we developed a complete device and demonstrated its performance under the solar illumination was appreciated by the jury of the Royal Society of Chemistry.

Are you continuing this project?

Martin Foldyna : Yes, I am still working in collaboration with some of the people from this team toward realizing an “artificial leaf”, i.e. a truly all-in-one system that you can put directly in the water, illuminate with sunlight and collect the gaseous solar fuels. Dipping perovskites into water would definitively damage them. That is why I am working with silicon-based nanowires as an alternative to perovskites. The technology to grow these nanowires is similar to that used for growing thin films and thus enables to achieve photoelectrodes with large surface areas and a good performance at a low cost. We have a great expertise about this at LPICM and are currently submitting a publication demonstrating the hydrogen production by such artificial leaf without the need of any external connection.

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*LPICM: a joint research unit CNRS, École Polytechnique - Institut Polytechnique de Paris