Scientists achieve perfect efficiency for water-splitting half-reaction

February 26, 2016 by Lisa Zyga feature
Under visible light illumination, the nanoscale photocatalysts perform the water-splitting reduction half-reaction with 100% efficiency. Credit: Lilac Amirav, Technion-Israel Institue of Technology

(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.

The researchers, Philip Kalisman, Yifat Nakibli, and Lilac Amirav at the Technion-Israel Institute of Technology in Haifa, Israel, have published a paper on the perfect efficiency for the water reduction half-reaction in a recent issue of Nano Letters.

"I strongly believe that the search for clean and renewable energy sources is crucial," Amirav told Phys.org. "With the looming energy crisis on one hand, and environmental aspects, mainly global warming, on the other, I think this is our duty to try and amend the problem for the next generation.

"Our work shows that it is possible to obtain a perfect 100% photon-to-hydrogen production efficiency, under illumination, for the photocatalytic 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."

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.

(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

In the new study, the researchers showed that the reduction half-reaction can be achieved with perfect efficiency on specially designed 50-nm-long nanorods placed in a water-based solution under visible light illumination. The light supplies the energy required to drive the reaction forward, with the nanorods acting as photocatalysts by absorbing the photons and in turn releasing electrons needed for the reaction.

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.

One of the keys to achieving the perfect efficiency was identifying the bottleneck of the process, which was the need to quickly separate the electrons and holes (the vacant places in the semiconductor left after the electrons leave), and remove the holes from the photocatalyst. To improve the charge separation, the researchers redesigned the nanorods to have just one platinum catalyst instead of two. The researchers found that the efficiency increased from 58.5% with two platinum catalysts to 100% with only one.

Going forward, the researchers plan to further improve the system. The current demonstration requires a very high pH, but such strong basic conditions are not always ideal in practice. Another concern is that the cadmium sulfide (CdS) used in the nanorod becomes corroded under prolonged light exposure in pure water. The researchers are already addressing these challenges with the goal to realize practical solar-to-fuel technology in the future.

"We hope to implement our design rules, experience and accumulated insights for the construction of a system capable of overall water splitting and genuine solar-to-fuel energy conversion," Amirav said. "The photocatalytic hydrogen generation presented here is not yet genuine solar-to-fuel energy conversion, as hole scavengers are still required. CdS is unfortunately not suitable for overall water splitting since prolonged irradiation of its suspensions leads to photocorrosion. We have recently demonstrated some breakthrough on this direction as well. The addition of a second co-catalyst, such as IrO2 or Ru, which can scavenge the holes from the semiconductor and mediate their transfer to , affords CdS-based structures the desired photochemical stability. I believe this is an important milestone."

Explore further: Core / shell photocatalyst with spatially separated cocatalysts for more efficient water splitting

More information: Philip Kalisman, et al. "Perfect Photon-to-Hydrogen Conversion Efficiency." Nano Letters. DOI: 10.1021/acs.nanolett.5b04813

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23 comments

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gkam
2.4 / 5 (5) Feb 26, 2016
How long before we have electrolyzers in our homes for our fuel cell vehicles?
KBK
1.7 / 5 (11) Feb 26, 2016
This only helps to illustrate that high levels of efficiency are viable in other areas where the results and research are not accepted by the mainstream.

This only points to 'alternative sciences' as being far more valid than mainstream acceptance will allow.

However, it is important to understand that mainstream textbook science is canonized lore, not facts. Real science, actual science accepts and promotes that science is devoid of facts and has only theory. Theory that is subject to change upon new findings.

functional scientists and theoreticians accept only theory and promote not one single fact. It can be no other way in any functional reality.

Therefore, there is no law or canonization, nor dogmatic components of science.

In essence, only fools, illiterates, and the unaware...or fifth column cloaked fascist brigands force and demand facts and law in science.

Many of you are not aware you are in a war zone, a war zone over suppressed technology and science.
greenonions
4.6 / 5 (18) Feb 26, 2016
Many of you are not aware you are in a war zone, a war zone over suppressed technology and science.
So what would happen if you got together with the 'others' who are aware of these suppressed technologies - and you 'unsuppressed' them? Would the black hawk choppers appear in the middle of the night - and you would disappear? It would sound like an opportunity for you guys to make a crap load of money.
dan42day
4.6 / 5 (10) Feb 26, 2016
Just think, with all that suppressed technology you could build white hawk choppers that ran on hydrogen fuel cells!
jaeuvi
5 / 5 (3) Feb 27, 2016
Excelent
rrrander
1 / 5 (1) Feb 27, 2016
"Captain, I require a small block of platinum, 5 or 6 pounds to be used as a dual-dynetic field-core..."
-Spock

Good luck with that.
neutronberg
not rated yet Feb 27, 2016
Great science, Bravo! Big like on science energy factor
Dug
4.3 / 5 (8) Feb 27, 2016
The article is a tad short on showing the complete mass balance reaction. Which means its also short on being able to determine its economic feasibility. These "breakthroughs" always end with some limiting caveat - " "The photocatalytic hydrogen generation presented here is not yet genuine solar-to-fuel energy conversion, as hole scavengers are still required. CdS is unfortunately not suitable for overall water splitting since prolonged irradiation of its suspensions leads to photocorrosion."

So, the short translation is that it works technically - except it is neither sustainable or economically feasible. Again we see that the vast majority of us can't distinguish between technical and economic feasibility - and or the necessity of having both.
HeuristicPerception
1 / 5 (2) Feb 27, 2016
anyone think applying different frequencies to this process would vary the results. ?
ive seen wonderful things done with crystals and frequencies.. ;)
gkam
4 / 5 (8) Feb 27, 2016
"So, the short translation is that it works technically - except it is neither sustainable or economically feasible. Again we see that the vast majority of us can't distinguish between technical and economic feasibility - and or the necessity of having both."
-----------------------------------

What? Excuse me, but it is an advancement, and is not billed as anything else, and includes the caveats, as you quoted.
Burnerjack
not rated yet Feb 27, 2016
"Captain, I require a small block of platinum, 5 or 6 pounds to be used as a dual-dynetic field-core..."
-Spock

Good luck with that.

I know a guy...
Whydening Gyre
5 / 5 (1) Feb 27, 2016
"Captain, I require a small block of platinum, 5 or 6 pounds to be used as a dual-dynetic field-core..."
-Spock

Good luck with that.

I know a guy...

... with a replicator?
Eikka
1 / 5 (3) Feb 28, 2016
What? Excuse me, but it is an advancement, and is not billed as anything else, and includes the caveats, as you quoted.


If you count every step taken as advancement, you might as well be walking in a circle.

Real progress is when something real comes out of the research, something that gives practical results rather than half-solutions that aren't practically feasible even in and of themselves. Often you just need multiple steps before you're actually going forwards, and the path of science is full of dead-ends and detours.

antialias_physorg
5 / 5 (9) Feb 28, 2016
Real progress is when something real comes out of the research

You have no clue how research works. It is small steps all the way. Even the things we call 'big moments in science' were the result of many small steps.

Don't be fooled how Hollywood portrays 'science' in superhero movies ("Oh, I just need to invent a new element...hold on...there....done"). That's not how real research works.

Even the detours and dead ends are valuable. For the latter you at least have now knowledge that something doesn't work (so you can skip repeating it in the future). For the former you never know whenit will become useful.

You've been on this site for a while, so I'm sure you've read a lot of articles that have had "using an almost forgotten method..." in there somewhere.

No amount of knowledge gained is useless. None.
gkam
1 / 5 (3) Feb 28, 2016
All those little findings can be used in conjunction with other phenomena to create synergism. The operative word is "integration", which means having operations and systems work together to become more than the sum of their parts, like an automobile, aircraft, or you.
Rydog
5 / 5 (3) Feb 28, 2016
Who knew Twinkies could be used to split water?
DonGateley
not rated yet Feb 28, 2016
Rate?
wishiwascool
5 / 5 (4) Feb 29, 2016
Real progress is when something real comes out of the research, something that gives practical results rather than half-solutions that aren't practically feasible even in and of themselves. Often you just need multiple steps before you're actually going forwards, and the path of science is full of dead-ends and detours.



When Faraday was displaying his discovery of inducing an electric current with magnets passing over copper wire a spectator asked "But of what use is this?" He simply replied, "Madam, of what use is a newborn babe?" In other words, you're full of horse shit.
Eikka
3 / 5 (2) Mar 04, 2016
You have no clue how research works. It is small steps all the way. Even the things we call 'big moments in science' were the result of many small steps.


Of course they are. That's completely besides the point.

When Faraday was displaying his discovery of inducing an electric current with magnets passing over copper wire a spectator asked "But of what use is this?" He simply replied, "Madam, of what use is a newborn babe?" In other words, you're full of horse shit.


And it WAS of no use until the work of many more men to produce generators and transmission lines and motors and radios etc. out of the basic invention. Just because you've demonstrated that something is possible doesn't mean you've actually done the hard work.

Again, you're just a mathematician in bed, looking at a glass of water on the table saying "the solution exists", while the house is on fire. The solution might exist, but simply pointing to it doesn't solve the problem.
Eikka
3 / 5 (2) Mar 04, 2016
No amount of knowledge gained is useless. None.


What does make knowledge useless is when you don't use it.

There's a real problem in the field of science and engineering called the "Valley of Death", which is the space and time between research and innovation, where fundamental discoveries fail to turn into actual products because the fundamental research doesn't address the question of economical or practical feasibility.

Funding is applied at one hand by the governments on the basic research to seek out possibilities and theoretical understanding, and on the other hand the private investors are eager to fund inventors with ready products, but there's nobody funding or looking for the go-between from research to inventions, so we simply get truckloads of interesting scientific papers and nothing ever comes out of it save by accident.

Eikka
5 / 5 (3) Mar 04, 2016
All those little findings can be used in conjunction with other phenomena to create synergism. The operative word is "integration", which means having operations and systems work together to become more than the sum of their parts, like an automobile, aircraft, or you.


That's perfect consultant jargon. The modalities of our conditions dictate that our outcomes can be successful. You want a banana sticker from the teacher for the presentation or what?

This is exactly the problem I mean. People shaking their jaws in the belief that if they say a lot of words, "raise awareness", then something must be happening and they're to be credited for it.
gkam
1 / 5 (3) Mar 04, 2016
I did not just teach this stuff. I acted. I earned a degree in the topic, worked in the field, and paid for my own power system and electric vehicle.

What is your game? Why do you try to disparage others and their experience?
baudrunner
not rated yet Mar 07, 2016
Who needs dilithium crystals? Just mine the comets for the raw materials to make your LOX and liquid hydrogen and refuel it yourself!

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