One of the beliefs of the scientists led by Kevin Sivula, of the Molecular Engineering of Optoelectronic Nanomaterials Laboratory at the Swiss Federal Institute of Technology in Lausanne, is that a sustainable society requires the development of new ways of storing renewable energies in chemical form. And this, both for mobility and for industry.
“ Daylight is the most abundant form of renewable energy, and we are working to develop economically viable ways to produce solar fuels “, he explains. We all probably remember having discovered the principle of photosynthesis in college or high school. This is the ability of plants to convert daylight into chemical energy by exploiting the carbon dioxide contained in the surrounding air. “ In broad outline, plants harvest CO2 and water from their environment and then, thanks to the energy pulse of sunlight, convert these molecules into sugars and starch. “, specifies the main editor of the study published in the scientific journal Advanced Materials.
With his teams from the molecular engineering laboratory of optoelectronic nanomaterials at the Ecole polytechnique fédérale de Lausanne, Kevin Sivula has developed a revolutionary hydrogen production device
A combination of 2 technologies
To reproduce the principle of photosynthesis, EPFL researchers simply created an artificial solar leaf. Transparent, porous and conductive, it takes the form of a gas diffusion electrode. It is what makes it possible to transform the water present in the air in the gaseous state into hydrogen, by exploiting natural light. The porosity serves to maximize contact with ambient humidity. The role of transparency is to optimize exposure to the sun of the semiconductor material.
Kevin Sivula had previously demonstrated that artificial photosynthesis can be achieved by generating hydrogen from water and sunlight with a photoelectrochemical (PEC) cell. Being able to stimulate a photosensitive material, for example a semiconductor, it was necessary until then to immerse the latter in a liquid solution for it to work, with the constraint of not being able to produce it on a large surface. The scientist adapted his principle to develop his gas diffusion electrode. Opaque until then, the latter was incompatible with PEC solar technology.
Realization of the concept
In a video of a little less than 5 minutes made in English, the main steps in the production of the transparent gas diffusion electrode are explained.
The basic material is a kind of glass wool, composed mainly of quartz fibers (or silicon oxide). It is introduced in the form of large marshmallows into a kitchen mixer, with a liquid solution. Once everything has been finely chopped, and after filtering, the fibers are assembled into a felt cake, by melting at high temperature, then coated with a transparent film of fluorine-enhanced tin oxide. The latter was chosen for its excellent conductivity, its robustness and the ease with which it can be produced on a large scale.
The result of these operations is this transparent, porous and conductive plate capable of best retaining the water molecules present in the ambient air and allowing photons to pass. It is then covered with a thin film of semiconductor materials which absorb light, although it appears opaque. The wafer is thus already operational by exposing it to the sun. To recover the hydrogen, it was integrated into a box, with a gas filtering membrane behind it.
European Sun-to-X project with Toyota
Very concerned about hydrogen mobility, Toyota Motor Europe is associated with the work of EPFL. What is the conversion efficiency of this demonstrator? It has not yet been finely measured. But the team of scientists imagines it, with the materials currently selected, at around 12%. This is less than the 19% of PEC cells that work by submerging them in water.
This value seems to be able to be improved with continued research aimed at finding the ideal fiber size, the best pore width, and the most efficient semiconductor and membrane materials. All of this work is being done as part of the European Sun-to-X project, focusing on developing new ways to convert hydrogen into liquid fuels.
About 10 years before commercial release
However, it would be necessary to improve the efficiency of the system while maintaining the ease and simplicity with which it can already be manufactured and implemented on a large scale today. So much so that the prototype was able to be produced entirely, step by step, by researchers at the Ecole polytechnique fédérale de Lausanne, who implemented the appropriate procedures.
About ten years would be needed to achieve a marketable system. Installed for example on the roofs of buildings in humid and sunny areas around the world, it would excel in producing green hydrogen at a particularly low cost.
And why not combine the principle with air dehumidification devices where necessary? By exploiting abundant resources, available around you, and free, the argument of the relatively low yield of hydrogen production no longer holds.
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Producing hydrogen from the humidity in the air is possible!
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