Swiss chemical engineers at the Swiss Federal Institute of Technology in Lausanne (EPFL) have made a breakthrough in technology by inventing a solar-powered artificial leaf, built on a transparent, porous electrode, with the ability to collect water from the air and convert it into hydrogen fuel.
How does the solar-powered artificial leaf work?
The solar-powered artificial leaf, this simple system, combining semiconductor-based technology with novel electrodes, is scalable and easy to set up. When the device is exposed to sunlight, it draws water from the air and produces hydrogen gas. Its transparent, porous and conductive gas diffusion electrodes enable this solar technology to convert gaseous water from the air into hydrogen fuel. It can be used as a renewable solar fuel, for example to power cars or heat homes.
To develop the solar-powered artificial leaf, researchers were inspired by the fact that plants are able to convert sunlight into chemical energy using carbon dioxide from the air. During photosynthesis, plants obtain carbon dioxide and water from their environment and, under sunlight, convert these chemicals into sugars and starches.
In earlier studies, Professor Kevin Sivula and his team demonstrated that it is possible to perform “artificial photosynthesis” by generating hydrogen fuel with sunlight and water using a device called a photoelectrochemical cell (PEC), but it is difficult to fabricate large-area PEC devices that use liquid.
Image credit: Alain Herzog
The researchers wanted to demonstrate that PEC technology can be adapted to capture water vapor from air instead of liquid water, which led them to develop their new transparent gas diffusion electrode. To fabricate transparent gas diffusion electrodes, the researchers started with a type of glass wool, an insulating material made of glass fiber that has a texture similar to textile wool. The glass wool was processed in a commercial kitchen blender and compressed into felt wafers by fusing the fibers together at high temperatures.
The wafers were coated with a thin transparent film of fluorine-doped tin oxide, known for its excellent conductivity. This resulted in a transparent, porous and conductive wafer, essential for maximizing contact with water molecules in the air and allowing photons to pass through, and then the wafer was again coated, now with a thin layer of semiconductor materials that absorb sunlight. This second layer allows light to pass through, even though it appears opaque. In this state, the coated wafer can now produce combustible hydrogen when exposed to sunlight.
Image credit: Alain Herzog
“The development of our prototype was challenging, as transparent gas diffusion electrodes had not been demonstrated before and we had to develop new procedures for each step,” explains Maria Caretti, lead author of the project.
The scientists did not formally study the solar-to-hydrogen efficiency in their demonstration, but acknowledge that it is modest for this prototype.
However, as each step is relatively simple and scalable, I believe our approach will open new horizons for a wide range of applications, starting with gas diffusion substrates for solar hydrogen production.
EPFL video of the solar-powered solar leaf.
In 2011 they had already developed an artificial leaf that generated oxygen, Julian Melchiorri, a graduate of the Royal College of Arts in London, presented an artificial leaf capable of generating oxygen in places where vegetation cannot be grown, for example, on a spacecraft.
This artificial leaf was the first synthetic leaf with the ability to create oxygen on its own. The invention can perform the same processes as real plants, through photosynthesis converting water, carbon dioxide and light into oxygen.
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