AsianScientist (Nov. 24, 2017) – In a study published in Angewandte Chemie International Edition, scientists in Japan have created a device that uses red and near-infrared (NIR) light to split water and produce hydrogen fuel.
Hydrogen gas is a promising ‘green’ fuel. The lightest chemical element, hydrogen is an efficient energy store and could potentially replace gasoline in vehicles. However, the element does not exist in large amounts in nature and must be produced artificially.
Hydrogen can be generated by splitting water into hydrogen and oxygen. There are many ways to do this, but among the cleanest and most attractive is using solar cells. These devices capture the energy of sunlight to drive the water-splitting reaction. Unfortunately, most solar cells only absorb shorter wavelengths of light which are highly energetic. This means that the lower energy range of the light spectrum, which includes light in the red, NIR and infrared wavelengths, goes to waste.
In this study, researchers at Kyushu University in Japan invented a device that runs on NIR light to split water and derive hydrogen. By introducing new electron orbitals into ruthenium atoms, they were able to make use of less energetic light, such as NIR light, to excite electrons and drive the reaction that produces hydrogen from water.
“It’s like adding rungs to a ladder—now the electrons in ruthenium don’t have so far to jump, so they can use lower energies of light such as red and NIR. This nearly doubles the amount of sunlight photons we can harvest,” explained corresponding author Professor Ken Sakai of Kyushu University.
Using an organic compound—hexagonal rings of carbon and nitrogen—to link three metal atoms into a single molecule, the researchers observed that not only were new ‘rungs’ created, the reaction also became more efficient due to spatial expansion of the light harvesting part of the molecule. Thus, the production of hydrogen was accelerated.
“It’s taken decades of efforts worldwide, but we’ve finally managed to drive water reduction to evolve H2 using NIR,” said Sakai. “We hope this is just the beginning; the more we understand the chemistry, the better we can design devices to make clean, hydrogen-based energy storage a commercial reality.”
The article can be found at: Tsuji et al. (2017) Near-Infrared Light-Driven Hydrogen Evolution from Water Using a Polypyridyl Triruthenium Photosensitizer.
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Source: Kyushu University; Photo: Shutterstock.
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