A device that can harvest water from the air and provide hydrogen fuel – entirely powered by solar energy – has been a dream for researchers for decades but now a team in Lausanne claims to have cracked it.

 

 

EPFL chemical engineer Kevin Sivula and his researchers developed a simple system that combines semiconductor-based technology with novel electrodes that have two key characteristics: they are porous, to maximise contact with water in the air; and transparent, to maximise sunlight exposure of the semiconductor coating.

 

When the device is simply exposed to sunlight, it takes water from the air and produces hydrogen gas. The results are published today in Advanced Materials.

 

Sivula said, “To realise a sustainable society, we need ways to store renewable energy as chemicals that can be used as fuels and feedstocks in industry. Solar energy is the most abundant form of renewable energy, and we are striving to develop economically-competitive ways to produce solar fuels.”

 

Inspiration from a plant’s leaf

 

In their research for renewable fossil-free fuels, the EPFL engineers in collaboration with Toyota Motor Europe, took inspiration from the way plants are able to convert sunlight into chemical energy using carbon dioxide from the air.

 

A plant essentially harvests carbon dioxide (CO2) and water from its environment, and with the extra boost of energy from sunlight, can transform these molecules into sugars and starches through photosynthesis. The sunlight’s energy is stored in the form of chemical bonds inside the sugars and starches.

 

The transparent gas diffusion electrodes developed by Sivula and his team, when coated with a light harvesting semiconductor material, 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 3D mesh of felted glass fibers.

 

Marina Caretti, lead author of the work, said, “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 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 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 researchers are focusing their efforts into optimising the system, considering ideal fiber, pore, semiconductor and membrane sizes.

 

Source:EnergyLiveNews