Harvesting hydrogen fuel from the Sun using Earth-abundant materials

September 25, 2014
When an electrical current is provided, water splits into oxygen and hydrogen. Credit: EPFL / LPI / Alain Herzog

The race is on to optimize solar energy's performance. More efficient silicon photovoltaic panels, dye-sensitized solar cells, concentrated cells and thermodynamic solar plants all pursue the same goal: to produce a maximum amount of electrons from sunlight. Those electrons can then be converted into electricity to turn on lights and power your refrigerator.

At the Laboratory of Photonics and Interfaces at EPFL, led by Michael Grätzel, where scientists invented dye that mimic photosynthesis in plants, they have also developed methods for generating fuels such as through solar water splitting.

To do this, they either use that directly split water into hydrogen and oxygen when exposed to sunlight, or they combine electricity-generating cells with an electrolyzer that separates the .

By using the latter technique, Grätzel's post-doctoral student Jingshan Luo and his colleagues were able to obtain a performance so spectacular that their achievement is being published today in the journal Science. Their device converts into hydrogen 12.3 percent of the energy diffused by the sun on perovskite absorbers – 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.

Bottled sun

This high efficiency provides stiff competition for other techniques used to convert solar energy. But this method has several advantages over others:

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Credit: EPFL

"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," explained Jingshan Luo. "However, our electrodes work just as well as the expensive platinum-based models customarily used."

On the other hand, the conversion of into hydrogen makes its storage possible, which addresses one of the biggest disadvantages faced by renewable electricity—the requirement to use it at the time it is produced.

"Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it," said Michael Grätzel. Such a 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. And the 12.3% conversion efficiency achieved at EPFL "will soon get even higher," promised Grätzel.

When an electrical current is applied, water splits into hydrogen and oxygen. Credit: EPFL / LPI / Alain Herzog

More powerful cells

These high efficiency values are based on a characteristic of perovskite cells: their ability to generate an open circuit voltage greater than 1 V (silicon cells stop at 0.7 V, for comparison).

"A voltage of 1.7 V or more is required for water electrolysis to occur and to obtain exploitable gases," explained Jingshan Luo. 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!" Luo adds.

The profusion of tiny bubbles escaping from the electrodes as soon as the solar 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.

Explore further: New solar cells serve free lunch

More information: "Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts," by J. Luo et al. Science, 2014. www.sciencemag.org/lookup/doi/10.1126/science.1258307

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2 / 5 (3) Sep 25, 2014
"Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it,

If only it was as simple as that. http://www.fsec.u..._gas.htm
1 / 5 (1) Sep 25, 2014
It makes sense in certain situations, as all alternative sources do.
1 / 5 (2) Sep 25, 2014
For cars it might be a problem but not for storing it for home cooking and heating uses.
5 / 5 (1) Sep 26, 2014
For cars it might be a problem but not for storing it for home cooking and heating uses.

Hydrogen pumped into homes is a massive explosion hazard, and it's going to leak a lot along the way anyhow due to its very small molecule that diffuses through metal pipelines. Rather, it's better to store it in low pressure gas bells near power stations, or be further modified into synthetic methane for use in cars.

not rated yet Sep 26, 2014
Yet if this technology was used at the home, then all of the above posts are irrelevant!! That is where this breakthrough is aimed. Home production and storage, the holy grail!!!
1 / 5 (3) Sep 26, 2014
Nonsense. The best fuel from the sun is Helium 3. Thousands of years to power society with fusion energy is available to mine on the moon. Only China has a plan to to so. If we are sane, (and, of course, by today's standards that is very much in doubt) the rest of humanity will join in.
not rated yet Sep 26, 2014
@thingumbobesquire So you are promoting a technology that has NOT been demonstrated, over a technology that HAS!!! Well done mate!!! Please keep practical science well in mind before casting opinions. I mean WOW lets tell everyone about anti-matter technology hey!!!! Nope practicality and affordability is what THIS article is promoting, not some STATE based super technology, way off in the future!!!!
5 / 5 (2) Sep 26, 2014
Yet if this technology was used at the home, then all of the above posts are irrelevant!! That is where this breakthrough is aimed. Home production and storage, the holy grail!!!

Unpressurized hydrogen has an energy density of 12.7 MJ/m^3 which is just about 3.5 kWh or the equivalent of four large marine batteries. An average household that spends 25,000 kWh a year for heating/cooling and electricity would need to dedicate on the order of 20 cubic meters for a hydrogen bell to contain enough energy for a single day. The necessary gas bladder would inflate to the volume of an entire room of about 100 sq.ft in floor area.

Pressurized hydrogen would take a smaller space, but it would run a much greater risk of leakage and would require energy to pressurize it.
not rated yet Nov 24, 2014
Eikka, I didn't say pump it to homes. I totally agree there. The current piping for propane or regular natural gas is rather inadequate. Having a home generator for it though would be a totally different scene. Nobody has come up with one that would efficient enough to really make it economically worthwhile yet though. A home tank wouldn't have to have high pressure. Just enough to maintain the systems of the house while it's being replenished by a hydrogen generator of some sort. Add some of that smelly perfume they add to indicate any leaks in the system and it wouldn't really be very different than running a propane or natural gas in a home heating or cooking setup.

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