Scientists at Ecole Polytechnique Fédérale de Lausanne (EPFL) have developed a new and efficient way of producing hydrogen fuel from sunlight and water. Connecting together solar cells made with a mineral called perovskite and the team’s low cost electrodes achieves a 12.3 percent conversion efficiency from solar energy to hydrogen.

The profusion of tiny bubbles escaping from the electrodes as soon as the solar cells are exposed to light say it better than words ever could: the combination of sun and water paves a promising and effervescent way for developing the energy of the future.

The 12.3 percent efficiency establishes a new non rare earth element process record. Absent platinum the costs for building a solar powered hydrogen production process is greatly reduced.

The Laboratory of Photonics and Interfaces at EPFL is led by Michael Grätzel, and is where scientists invented dye solar cells that mimic photosynthesis in plants. Now they have also developed a method for generating fuel such as hydrogen through solar water splitting.

Grätzel’s post-doctoral student Jingshan Luo and his colleagues using the new process were able to obtain a performance so spectacular that their achievement has been published in the journal Science. This efficiency number is no small breakout for the technology.

The team’s device converts into hydrogen at 12.3 percent of the energy diffused by the sun on perovskite absorbers – perovskite is a compound that can be obtained in the laboratory from common materials, such as those used in conventional car batteries, eliminating the need for rare-earth metals in the production of usable hydrogen fuel.

There is a wide array of research underway to optimize solar energy’s performance. There are more silicon photovoltaic panels, dye-sensitized solar cells, concentrated cells and thermodynamic solar plants all pursuing the same goal of producing a maximum amount of electrons from sunlight. Those electrons can then be converted into electricity to run the lights, power up appliances and energize our electronic devices.

The new process provides stiff competition for other techniques used to convert solar energy with several advantages.

Nickel Iron Hydrogen Production Electrodes.  Image Credit:©Alain Herzog - EPFL.  Click image for the largest view.

Nickel Iron Hydrogen Production Electrodes. Image Credit:©Alain Herzog – EPFL. Click image for the largest view.

Jingshan Luo explains, “Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap. However, our electrodes work just as well as the expensive platinum based models customarily used.”

In the next step, the conversion of solar energy into hydrogen, makes solar energy storage possible. That addresses one of the biggest disadvantages faced by renewable electricity – the requirement to use the energy at the time it is produced.

Grätzel points out, “Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it.” Hydrogen gas can indeed be burned – in a boiler or engine – releasing only water vapor. It can also pass into a fuel cell to generate electricity on demand. Grätzel promises in the press release the 12.3% conversion efficiency achieved at EPFL “will soon get even higher”.

The breakout efficiency is based on a characteristic of perovskite cells which is their ability to generate an open circuit voltage greater than 1V while compared to silicon cells that stop at 0.7V.

Jingshan Luo explains, “A voltage of 1.7V or more is required for water electrolysis to occur and to obtain exploitable gases.” To get these numbers, three or more silicon cells are needed, whereas just two perovskite cells are enough. As a result, there is more efficiency with respect to the surface of the light absorbers required. “This is the first time we have been able to get hydrogen through electrolysis with only two cells!” exclaims Luo.

The solar driven hydrogen production effort is starting to look very good, indeed.


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