Researchers mimick photosynthesis to produce hydrogen fuel

A new technique developed by researchers at Michigan Technological University allows them to convert visible light more efficiently, essentially mimicking photosynthesis in order to produce hydrogen fuel in a more sustainable manner than ever before.
Yun Hang Hu, the Charles and Carroll McArthur professor of Materials Science and Engineering at Michigan Tech, and his PhD student Bing Han explained their technique in a recent edition of the Journal of Physical Chemistry. The key, they wrote in their new study, is to fully understand the interaction between the catalyst, visible light, and a sacrificial molecule.
Typically, artificial photosynthesis is less efficient because of the difficulties in converting visible light into other energy. However, Hu and Han believe that their method solves this issue and could make the sustainable production of hydrogen fuels more efficient than ever.
New technique increases efficiency, overall yield
As the researchers explain, in order to produce hydrogen molecules, scientists set out to split a water molecule by having it capture an excited electron. This is accomplished by bouncing solar energy off titanium dioxide (TiO2) to get the electron excited, then taking a second electron from methanol (CH3OH) and using it to keep the first from returning to its original position.
This is the sacrificial agency, and it prevents the photo-excited electron from upending the whole process by returning to its starting point in the valence band. These interactions deliver hydrogen (H2) molecules, and since UV light makes up only a fraction of solar energy, it is essential to use visible light. Using their new technique, Hu and Han were able to increase the efficiency and the overall yield of the process by up to two magnitudes greater than previous experiments.
Hu explained that it was “a two-part process” that used black titanium dioxide (with one percent platinum) as the catalyst. During their experiments, this catalyst attached to a substrate of silicon dioxide, and by using a “light-diffuse-reflected surface” for the silicon dioxide, they were able to make it trap light waves and increase absorption by 100 times previous levels.
One step closer to complete photosynthesis replication
However, using visible light in the absorption process shortens the band gap so that the electron has less distance to travel, but also reduces methanol’s oxidation reaction and making it harder for its electron to fill the gap in the valence band. To overcome this, they had to add a little heat to the process forcing them to change the process.
Instead of regular liquid water, they used steam. The steam was pushed into a chamber, where it collided with a disk of roughened silicon dioxide which the study authors explained was studded with black titanium dioxide-platinum catalyst. The electrons were excited by visible light, which allowed the hydrogen to be siphoned off. Their research also created a new light-heat hybrid type of process which brings researchers one step closer to mimicking photosynthesis.
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