Scientists achieve perfect efficiency for water-splitting half-reaction

[Jim__]

From phys.org:

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[center](Left) Transmission electron microscope images of the nanorod photocatalysts with (a) one and (b) two platinum tips. (Right) A comparison of the efficiencies shows the advantage of using a single platinum tip. Credit: Kalisman, et al. ©2016 American Chemical Society[/center]
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(Phys.org)—Splitting water is a two-step process, and in a new study, researchers have performed one of these steps (reduction) with 100% efficiency. The results shatter the previous record of 60% for hydrogen production with visible light, and emphasize that future research should focus on the other step (oxidation) in order to realize practical overall water splitting. The main application of splitting water into its components of oxygen and hydrogen is that the hydrogen can then be used to deliver energy to fuel cells for powering vehicles and electronic devices.

...

When an H₂O molecule splits apart, the three atoms don't simply separate from each other. The full reaction requires two H₂O molecules to begin with, and then proceeds by two separate half-reactions. In the oxidation half-reaction, four individual hydrogen atoms are produced along with an O₂ molecule (which is discarded). In the reduction half-reaction, the four hydrogen atoms are paired up into two H₂ molecules by adding electrons, which produces the useful form of hydrogen: H₂ gas.

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The 100% efficiency refers to the photon-to-hydrogen conversion efficiency, and it means that virtually all of the photons that reach the photocatalyst generate an electron, and every two electrons produce one H₂ molecule. At 100% yield, the half-reaction produces about 100 H2 molecules per second (or one every 10 milliseconds) on each nanorod, and a typical sample contains about 600 trillion nanorods.

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[Fairgo]

1. Fascinating

thanks for that

[DetlefK]

2. Boring number-crunching:

600*10^12 nanorods * 100 molecules per second = 6*10^16 molecules per second

1 mol is approx. 6*10^23 molecules, so that's 10^7 seconds of sunlight we need per sample.

If we increase the sample-size by a factor of 100, we are down to 10^5 seconds of sunlight equalling 1 mol of H2.

And 10^5 seconds is a bit less than 30 hours.




Damn, it would work! It wouldn't be enough H2 to supply a fleet of cars, but it would be enough to provide fuel for an isolated outpost or village.

[Jim__]

3. Yes, and even more boring - reading - 360,000 moles of hydrogen per hour per mole of catalyst.

From the article:

"Our work shows that it is possible to obtain a perfect 100% photon-to-hydrogen production efficiency, under visible light illumination, for the photocatalytic water splitting reduction half-reaction. These results shatter the previous benchmarks for all systems, and leave little to no room for improvement for this particular half-reaction. With a stable system and a turnover frequency of 360,000 moles of hydrogen per hour per mole of catalyst, the potential here is real."

[DetlefK]

4. WANT! NOW!