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Saturday, 25 January 2020

Researchers find way to harness the entire visible spectrum for energy production

For the very first time, scientists have demonstrated that it is possible to collect energy from the entire visible spectrum of sunlight and transform it quickly and efficiently into hydrogen. In fact, they have developed a single molecule that can efficiently absorb sunlight and also act as a catalyst to transform solar energy into hydrogen. A clean alternative to fossil fuels (for, in particular, motor vehicles).

This new molecule collects energy from the entire visible spectrum and can harness more than 50% more solar energy than current solar cells. This discovery could well help humanity move from fossil fuels to energy sources that do not contribute to climate change.

“  The idea is to use the photons from the sun and transform them into hydrogen. Simply put, we collect energy from sunlight and store it in chemical bonds so it can be used later, "said Claudia Turro, professor of chemistry and director of the center at Ohio State University for chemical and biophysical dynamics (and who also directed this research). Namely, that photons are the elementary particles of light, and contain a certain amount of energy.

Thanks to this study, for the very first time, it has been demonstrated that it is possible to collect energy from the entire visible spectrum of sunlight, including low energy infrared ( part of the solar spectrum that had previously been difficult to collect) and transform it quickly and efficiently into hydrogen.

Hydrogen is a clean fuel, which means that it does not produce carbon or carbon dioxide as a by-product of its use. "  What makes it work is that the system is able to put the molecule in an excited state, where it absorbs the photon and is able to store two electrons to produce hydrogen. This storage of two electrons in a single molecule, as well as this use to produce hydrogen, is unprecedented,  ”said Turro.

Indeed, transforming the Sun's energy into fuel, for example to power a vehicle, first requires an energy collection mechanism. Then, this energy can be converted into fuel. The conversion requires a catalyst. In short: this is a device which accelerates a chemical reaction allowing the conversion of solar energy into a usable energy vector (in this case hydrogen).

Most of the previous attempts to collect solar energy and transform it into hydrogen have focused on higher energy wavelengths (like ultraviolet, for example). The latter have also relied on catalysts always involving two molecules (or more), which exchange electrons (energy) to produce fuel from solar energy. But a large part of this energy is lost in the exchange, which makes these multimolecular systems less efficient.

In addition, the few other attempts that relied on a single molecule catalyst were also ineffective "partly because they did not collect energy from the entire visible spectrum of the sun, and also because the catalysts themselves degraded quickly, "said Turro.

A system 25 times more efficient than current technologies

Now, Turro's research team has discovered how to make a catalyst from a single molecule, a form of rhodium (a chemical element), which means less energy is lost. The researchers also understood how to collect energy from the near infrared to the ultraviolet, more than the entire visible spectrum.

According to the researchers, the system they designed is nearly 25 times more efficient with low-energy near-infrared light than single-molecule systems operating with ultraviolet photons.

As part of this study, the researchers used LEDs to illuminate acid solutions containing the active molecule, and discovered that hydrogen was produced.

" I think the reason it works is because the molecule is difficult to oxidize,  " says Turro. "  And we have to have renewable energy. Just imagine, if we could use sunlight for our energy needs instead of coal, gas or oil, what we could do to fight climate change, ”added Turro.

But before the research team's results can be applied in the real world, "there is still a lot of work to do," admits Turro. Indeed, rhodium is a rare metal and the production of catalysts using it is expensive. The team is therefore working to improve this molecule to produce hydrogen over a longer period of time and to develop a catalyst exploiting less rare elements.


Article: Single-chromophore single-molecule photocatalyst for the production of dihydrogen using low-energy light

T. J. Whittemore, C. Xue, J. Huang, J. C. Gallucci & C. Turro

Nature Chemistry (2020)

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