This device sucks water out of thin air and gives out hydrogen fuel

Sunlight-driven hydrogen fuel will power our future.
Rupendra Brahambhatt
Hydrogen power storage on a hill.
Hydrogen power storage on a hill.


What if I told you there is a device that can produce hydrogen fuel out of humid air just by using solar energy? The world would go crazy for any such device because who doesn’t want clean fuel for free, right?

A team of researchers from the Swiss Federal Institute of Technology (EPFL) Lausanne has created one such device which, when exposed to sunlight, extracts the water content (humidity) of the air and gives out hydrogen gas. This gas can be further used as renewable solar fuel to power various applications, according to the press release.

Principal investigator of the study and professor at EPFL, Kevin Sivula, told IE that the device is still in the development phase and it will take about ten years before this technology becomes commercially available. However, the current study represents a big step in our search for eco-friendly and sustainable fossil-free fuel.  

How does the solar fuel device work?

The study authors took their inspiration from photosynthesis, the natural process through which plants prepare their food using sunlight. During photosynthesis, plants use CO2 and water from their surrounding, and under sunlight, they convert these chemicals into starch and sugar, which is their food.

In one of their previous studies, Professor Sivula and his team employed a device known as a photoelectrochemical (PEC) cell. They demonstrated artificial photosynthesis that involved producing hydrogen fuel from liquid water and sunlight using the PEC cell. This device used photosensitive semiconductor material that triggered such chemical reactions under sunlight that split water into H2 and O2.

However, such devices were not scalable and very complex to build. The researchers then noticed that the cells work better with gases than liquids. So they decided to use the PEC technology for extracting humidity out of the air instead of using liquid water directly, and this led them to the current study.   

Professor Sivula and his team developed transparent gas diffusion electrodes and coated them with a semiconductor material capable of capturing and processing sunlight. Unlike conventional electrodes that are composed of materials that are opaque to sunlight, transparent electrodes are made of 3D glass fibers.   

This is the first study that uses transparent diffusion gas electrodes as a suitable substrate for a PEC cell. This whole setup works like an artificial leaf that sucks water out of thin air and produces hydrogen gas. 

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The energy from the sun is stored by the leaf as hydrogen bonds in the produced gas. This energy can be further utilized as a green and clean solar fuel. 

A small step toward a big goal

This device sucks water out of thin air and gives out hydrogen fuel
Professor Sivula in his lab.

Well, at first, the idea of producing solar-hydrogen fuel from thin air may sound very simple, but in reality, it is still a complex process. Even just to demonstrate their idea, the study authors had to employ several principles and concepts of semiconductors physics, optoelectronics, catalysis, and mass transfer altogether in a controlled environment. 

According to professor Sivula, the device would probably take 10 or more years of further research to become a mainstream technology. 

The simplest explanation of the mechanism which makes the artificial leaf work is that sunlight absorbed by its semiconductor material produces an excited state that can, under the right conditions, react with water to produce H2 and O2.  

“We have just made an initial demonstration. the efficiency is very low (less than 1 %) much more work is needed. We hope that our result will generate interest in this approach and that other research groups will participate in advancing these gas-phase photoelectrochemical cells, Professor Sivula told IE

The researchers will continue to optimize the device preparation steps and try to advance its performance. They also plan to make a larger-scale demonstrator device as part of an EU (European Union) project. 

The study is published in the journal Advanced Materials.

Study Abstract:

Gas diffusion electrodes are essential components of common fuel and electrolysis cells but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance and thus limit the development of gas-phase based photoelectrochemical devices. Herein, the simple and scalable preparation of F-doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is reported. Using 2–5 µm diameter fibers at a loading of 4 mg cm−2, the resulting substrates have porosity of 90%, roughness factor of 15.8, and Young's Modulus of 0.2 GPa. A 100 nm conformal coating of FTO via atmospheric chemical vapor deposition gives sheet resistivity of 20 ± 3 Ω sq−1 and loss of incident light of 41% at illumination wavelength of 550 nm. The coating of various semiconductors on the substrates is established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and conjugated polymers (dip coating), and liquid-phase photoelectrochemical performance commensurate with flat FTO substrates is confirmed. Finally, gas phase H2 production is demonstrated with a polymer semiconductor photocathode membrane assembly at 1-Sun photocurrent density on the order of 1 mA cm−2 and Faradaic efficiency of 40%.

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