Lausanne University of Technology offers new way for H2 transition

For the transition to a sustainable energy system, techniques are needed to convert renewable energy, such as solar energy, into fuels, such as hydrogen. This is important for energy storage and applications that cannot yet go without power, such as aircraft.

Hydrogen can already be produced sustainably, for example by using power from solar panels to power a so-called electrolyser that splits liquid water into hydrogen and oxygen. “But that’s still too expensive to compete with current hydrogen production from natural gas,” says chemical technologist Kevin Sivula of the Lausanne University of Technology in Switzerland. “That is why we are researching techniques that could be less expensive.”

In this, the researchers at the Lausanne University of Technology have now taken an important step. They have developed electrodes that are porous and transparent so that sunlight and water from the air can reach the semiconductor to allow a photoelectrochemical reaction to take place there that produces hydrogen. The results appeared Wednesday in the journal Advanced Materials.

Previously, this was not possible because the necessary electrodes were not transparent enough to allow sunlight to pass through for the photoelectrochemical reaction.

“The advantage of our system is that we do not use liquid water,” says Sivula. In systems that use liquid water, you cannot simply throw water out of a lake or ocean. You need to purify it first. Sivula: “we don’t have that problem because we condense water from the air. That immediately provides clean water.”

The basis for the transparent electrodes is a kind of glass wool that the researchers compress and heat to make a compact, spongy structure. On top of that, they apply a material that is transparent and electrically conductive – a tricky combination. Then they cover it with a light-absorbing semiconductor. There they add a catalyst that allows the hydrogen-producing reaction to take place.

This whole thing is porous, so that there is enough surface on which water vapor can precipitate. And it is transparent enough for the sunlight to pass through for the photoelectrochemical reaction. Tests with a small-scale prototype show that this system does indeed produce hydrogen gas.

The researchers have not yet looked at which humidity is required at a minimum. “Higher humidity, such as in the tropics or above sea level, probably gives the best result,” says Sivula. “But even in the desert, there is enough water in the air to produce hydrogen.”

In addition, the device is supposed to take advantage of the changing conditions of day and night. at night, when it cools and the relative humidity rises, the system can absorb water from the air and then produce hydrogen during the day, when the sun is shining.
Efficiency still too low

A future in which these devices produce hydrogen on a large scale and cheaply is still a long way off, Sivula admits. “We now have a low-cost system that is scalable. But the efficiency is still too low.”

The prototype had an efficiency of about 1 percent for converting sunlight into hydrogen. It has to be at least ten times better before it becomes commercially interesting.

Joost Reek, professor of Chemistry at the University of Amsterdam and not involved in the research, agrees: “it still needs to be further optimized and developed, but it looks promising.”

“Theoretically, it seems possible,” says Sivula. There is still a lot to optimize the materials and construction. Future experiments will have to show whether researchers can boost efficiency without raising costs.