Scientists have taken a major step in direction of creating a tool that may harvest water from the air and generate hydrogen gasoline utilizing photo voltaic vitality. They developed a system that mixes semiconductor-based expertise with novel electrodes which can be porous and clear to maximise water-air contact and photo voltaic publicity of the semiconductor coating. When uncovered to daylight, the gadget takes water from the air and produces hydrogen gasoline.
A tool that may harvest water from the air and supply hydrogen gasoline — powered completely by photo voltaic vitality — has been a dream of researchers for many years. Now, EPFL chemical engineer Kevin Sivula and his staff have taken a major step in direction of bringing this imaginative and prescient nearer to actuality. They’ve developed a artistic however easy system that mixes semiconductor-based expertise with novel electrodes which have two key traits: they’re porous, to maximise the contact of water with air; and clear, to maximise daylight publicity of the semiconductor coating. When the gadget is uncovered to daylight, it takes water from the air and produces hydrogen gasoline. The outcomes had been revealed on 4 January 2023 at Superior Supplies.
What’s new? It’s their novel gasoline diffusion electrodes, that are clear, porous, and conductive, that allow this solar-powered expertise to show water – in its gasoline state from air – into hydrogen gasoline.
“To understand a sustainable society, we’d like methods to retailer renewable vitality as chemical substances that can be utilized as fuels and industrial feedstock. Photo voltaic vitality is probably the most plentiful type of renewable vitality, and we try to develop economically aggressive methods to supply photo voltaic gasoline,” stated Sivula of EPFL’s Laboratory for Molecular Engineering of Optoelectronic Nanomaterials and principal investigator of the research.
Kevin Sivula in his lab. Supply: Alain Herzog / EPFL
Inspiration from plant leaves
Of their analysis for renewable fossil-free fuels, EPFL engineers in collaboration with Toyota Motor Europe, took inspiration from the way in which crops are in a position to convert daylight into chemical vitality utilizing carbon dioxide from the air. A plant primarily harvests carbon dioxide and water from its atmosphere, and with added vitality from daylight, can convert these molecules into sugars and starches, a course of often known as[{” attribute=””>photosynthesis. The sunlight’s energy is stored in the form of chemical bonds inside of the sugars and starches.
The transparent gas diffusion electrodes developed by Sivula and his team, when coated with a light harvesting semiconductor material, indeed act like an artificial leaf, harvesting water from the air and sunlight to produce hydrogen gas. The sunlight’s energy is stored in the form of hydrogen bonds.
Instead of building electrodes with traditional layers that are opaque to sunlight, their substrate is actually a 3-dimensional mesh of felted glass fibers.
Marina Caretti, lead author of the work, says, “Developing our prototype device was challenging since transparent gas-diffusion electrodes have not been previously demonstrated, and we had to develop new procedures for each step. However, since each step is relatively simple and scalable, I think that our approach will open new horizons for a wide range of applications starting from gas diffusion substrates for solar-driven hydrogen production.”
From liquid water to humidity in the air
Sivula and other research groups have previously shown that it is possible to perform artificial photosynthesis by generating hydrogen fuel from liquid water and sunlight using a device called a photoelectrochemical (PEC) cell. A PEC cell is generally known as a device that uses incident light to stimulate a photosensitive material, like a semiconductor, immersed in liquid solution to cause a chemical reaction. But for practical purposes, this process has its disadvantages e.g. it is complicated to make large-area PEC devices that use liquid.
Sivula wanted to show that the PEC technology can be adapted for harvesting humidity from the air instead, leading to the development of their new gas diffusion electrode. Electrochemical cells (e.g. fuel cells) have already been shown to work with gases instead of liquids, but the gas diffusion electrodes used previously are opaque and incompatible with the solar-powered PEC technology.
Now, the researchers are focusing their efforts into optimizing the system. What is the ideal fiber size? The ideal pore size? The ideal semiconductors and membrane materials? These are questions that are being pursued in the EU Project “Sun-to-X”, which is dedicated to advance this technology, and develop new ways to convert hydrogen into liquid fuels.
Making transparent, gas-diffusion electrodes
In order to make transparent gas diffusion electrodes, the researchers start with a type of glass wool, which is essentially quartz (also known as silicon oxide) fibers and process it into felt wafers by fusing the fibers together at high temperature. Next, the wafer is coated with a transparent thin film of fluorine-doped tin oxide, known for its excellent conductivity, robustness and ease to scale-up. These first steps result in a transparent, porous, and conducting wafer, essential for maximizing contact with the water molecules in the air and letting photons through. The wafer is then coated again, this time with a thin-film of sunlight-absorbing semiconductor materials. This second thin coating still lets light through, but appears opaque due to the large surface area of the porous substrate. As is, this coated wafer can already produce hydrogen fuel once exposed to sunlight.
The scientists went on to build a small chamber containing the coated wafer, as well as a membrane for separating the produced hydrogen gas for measurement. When their chamber is exposed to sunlight under humid conditions, hydrogen gas is produced, achieving what the scientists set out to do, showing that the concept of a transparent gas- diffusion electrode for solar-powered hydrogen gas production can be achieved.
While the scientists did not formally study the solar-to-hydrogen conversion efficiency in their demonstration, they acknowledge that it is modest for this prototype, and currently less than can be achieved in liquid-based PEC cells. Based on the materials used, the maximum theoretical solar-to-hydrogen conversion efficiency of the coated wafer is 12%, whereas liquid cells have been demonstrated up to 19% efficient.
Reference: “Transparent Porous Conductive Substrates for Gas-Phase Photoelectrochemical Hydrogen Production” by Marina Caretti, Elizaveta Mensi, Raluca-Ana Kessler, Linda Lazouni, Benjamin Goldman, Loï Carbone, Simon Nussbaum, Rebekah A. Wells, Hannah Johnson, Emeline Rideau, Jun-ho Yum and Kevin Sivula, 28 November 2022, Advanced Materials.
DOI: 10.1002/adma.202208740
