A Promising Catalyst for Solar-Based Hydrogen Energy Production

December 2, 2008, Phys.org feature

(PhysOrg.com) -- Scientists have found that a polymer material is an excellent catalyst in a process to produce hydrogen fuel using sunlight and water. The material meets the basic requirements for an ideal catalyst -- including being abundant, easy to work with, and non-toxic -- and could help this "green" alternative-energy production method become mainstream.

Creating hydrogen gas by splitting water (H2O) molecules with solar energy is a promising way of generating hydrogen fuel, which, by either being burned directly or used in fuel cells, can power many types of vehicles, including automobiles, buses, and even airplanes.

The study's corresponding scientist is Xinchen Wang, a chemist affiliated with the Max-Planck Institute of Colloids and Interfaces in Potsdam, Germany, and Fouzhou University in Fouzhou, China.

"The search for a suitable semiconductor material to use as a catalyst in this process has been a main goal of materials-science research," said Wang to PhysOrg.com. "In addition to being a plentiful, versatile, and safe material, the catalyst should also be stable when in contact with water and able to absorb visible light. The material we chose fits these requirements."

The inorganic catalysts developed in the last 30 years have been metal-based and often require the use of pricey precious metals to aid in the catalysis process. Synthetic polymer materials have also been developed, but they only work with light in the ultraviolet region -- a small fraction of the solar spectrum -- and their performance is mediocre.

The material investigated by Wang and his colleagues is carbon nitride that has been "polymerized" into molecule chains. This form of carbon nitride was first synthesized in 1834. The group went a step further, using a heating/condensation process to force the chains to form layered sheets with structures similar to graphite, a highly ordered form of carbon.

The carbon nitride was then powdered and added to water containing a "reagent" material that donates electrons to the catalysis reaction. When the mixture is illuminated, the water molecules split into positive hydrogen ions and oxygen atoms. The catalyst's carbon atoms assist by providing locations for the hydrogen-ions to reduce to H2 -- a process by which the nitrogen atoms "donate" electrons to the ions so they can reform into diatomic hydrogen. The nitrogen atoms help with the opposite process, oxidation, helping the oxygen atoms form O2 molecules.

The group's tests show that polymeric carbon nitride absorbs both ultraviolet and visible light and, although its performance yielded varying H2 production rates from batch to batch, that it is an effective catalyst even without the presence of platinum or other noble metals.

"Our result opens new pathways for the search of energy production schemes, using polymeric organic semiconductor structures that are cheap, stable, and commonly available," said Wang.

This study is published in the November 9 online edition of Nature Materials.

More information: Xinchen Wang, Kazuhiko Maeda, Arne Thomas, Kazuhiro Takanabe, Gang Xin, Johan M. Carlsson, Kazunari Domen & Markus Antonietti, Nature advance online publication DOI:10.1038/nmat2317

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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dan42day
1 / 5 (2) Dec 03, 2008
Did anyone else come to a screeching halt when they read 'water containing a "reagent" material'? So what is it? Plutonium? Sarin gas? What's the catch?
FindAlex
not rated yet Dec 03, 2008
Probably any good reducing agent?
deatopmg
2 / 5 (4) Dec 03, 2008
.....and how does one keep UV from catalyzing the mixed O2 and H2 recombination to water before the 2 can be separated?

Nice ACADEMIC work though.
theophys
2.3 / 5 (6) Dec 03, 2008
I think it's generally a bad idea to rely on water for powering cars, busses, and airplanes. We already have some severe water problems here in Nevada and something like this could potentialy cause similar problems in other regions. If we could find another abundent chemical that is less vital to life on Earth, we should probably consider using that first.
phlipper
4.8 / 5 (5) Dec 03, 2008
I think it's generally a bad idea to rely on water for powering cars, busses, and airplanes. We already have some severe water problems here in Nevada and something like this could potentialy cause similar problems in other regions. If we could find another abundent chemical that is less vital to life on Earth, we should probably consider using that first.

I'm trying to be kind here so I'll just say that your statement astonishes me. If you're that concerned about water, take a drink from the tailpipe of your hydrogen burning vehicle. The combustion product of hydrogen and oxygen is....you guessed it--WATER! If all the vehicles in Nevada were burning hydrogen, there would be so much steam rising from the tailpipes that you would be praying for it to stop raining!! The other solution would be to move out of the desert.
FindAlex
3.3 / 5 (3) Dec 03, 2008
You could always condense the water vapor after the reaction. It could be used as recycled water, already clean recycled water.
Damon_Hastings
4 / 5 (4) Dec 04, 2008
Velanarris: the water emitted by a hydrogen car comes from hydrogen which originally came from water. So the result is zero net emission. And in fact, the water could be sequestered just as CO2 emissions can be sequestered -- but that would seem rather silly. :-P Any sequestration would ultimately just cause the oceans to evaporate a tiny bit more to replace the water you hid away!
Damon_Hastings
3.7 / 5 (3) Dec 04, 2008
You could always condense the water vapor after the reaction. It could be used as recycled water, already clean recycled water.


How would you suggest doing that on a car, train, boat, or any other mobile object?


Um, couldn't you just cool it? I see liquid water dripping from tailpipes all the time, so it must not be that hard...
FindAlex
5 / 5 (2) Dec 04, 2008
You could run the vapor through a series of small metal tubes exposed to the passing by air. Also known as a radiator.
FindAlex
5 / 5 (2) Dec 04, 2008
Well then maybe we shouldn't include a steering wheel either and we can just drive in straight lines everywhere. I am just saying, if you are worried about water vapor emissions, there are ways of dealing with it (it also occasionally rains on earth). Also, you could just use a light weight metal such as aluminum for the radiator.
runninglate
4.3 / 5 (6) Dec 04, 2008
I need to point out the obvious, or not so obvious to Velanarris. Steam (water vapor) emitted at sea level will precipitate out of the air as the steam cools. Unlike, H20, CO2 is thoroughly a gas in our atmosphere (boiling point of -109 deg. F. at STP). So, as C02 emisions cool, they will not precipitate. I'm not really sure what does happen to the CO2 emissions, but ultimately, I'm under the impression that much of it does stay up there, and other CO2 dissolves in the ocean to form H2CO3 (acidifying of oceans) and other is consumed by plant life.
Star_Gazer
3.3 / 5 (7) Dec 05, 2008
Which is hilarious seeing as water vapor is 100x the greenhouse gas that CO2 is.

So to stop vehicular CO2 production, you'll supplant is with H2O.

Utter genius.....


Absolutely! We should cover rivers and oceans with plastic film to avoid that awful greenhouse gas emission called water vapor.
theophys
5 / 5 (3) Dec 06, 2008
The problem is that there is too much CO2 in the atmosphere and it is increasing exponetialy with due nto huan activity. Turns out that CO2 isn't the nastiest of all the greenhouse gasses. Methane, for example, keeps much more heat on Earht than does CO2. There's just so little methane in the air compared to CO2 that its contribution to climate change negligible for the time being. H2O, it's true, does do a great job of reflecting light and heat. It also does a great job of storing heat. In fact, the reason why our planet isn't a trubulent ball of death like Venus is because our oceans are so great at capturing, storing, and negating all the wonderful heat from the sun. I'm going to go ahead and say that water has paid its debt to society for reflecting a little heat back at the earth now and then.
Soylent
5 / 5 (5) Dec 06, 2008
Which is hilarious seeing as water vapor is 100x the greenhouse gas that CO2 is.


Hey genius, the half-life of water vapour in the atmosphere before percipitating out as fog, clouds or rain is some ~10 000 times shorter than CO2.
Damon_Hastings
2.7 / 5 (3) Dec 06, 2008
Now let me ask you guys why do you think CO2 is such a suspect if a known element that has a far stronger greenhouse effect is perfectly ok?


Excess water vapor will tend to precipitate out of the atmosphere a lot faster than excess CO2 does. In fact, you might have a hard time finding CO2 precipitation on Earth. ;-)

CO2 is different from water because the Earth is not full of vast reservoirs of liquid CO2 ready to evaporate to instantly replace whatever CO2 gas we manage to take out of the air -- nor to capture whatever excess CO2 we might produce. Thus, we humans actually have a fighting chance of changing the amount of CO2 in the atmosphere (positively or negatively!)

And you're right, the oceans can absorb CO2 -- but as I'm sure you know, global warming actually *reduces* the oceans' capacity for storing CO2. ;-) The result is that the oceans, while still gaining CO2, are gaining it more slowly than the atmosphere is.

As for CO2 in the atmosphere, runninglate, when it rains the CO2 is pulled out of the air and absorbed by the falling water.


Yes, but the ocean itself is at the same time releasing CO2 back into the atmosphere. It's a cycle, and it roughly cancels out. (It has to, or else the oceans would just keep filling up with CO2 until they're more acidic than a lead battery.) That said, this cycle, too, has been disrupted -- and the oceans *are* absorbing CO2 and *are* becoming more acidic. Hence the widespread death of corals. The oceans act as a "carbon sink", and this does help slow down the increase in atmospheric CO2 -- but not nearly enough.

And FYI Damon, technically all the carbon from fossil fuels came from CO2 in the air, does that mean they're also a net zero emission fuel?


Ha, ha. ;-) Seriously, though, the carbon from fossil fuels has typically been trapped underground for millions of years before humans release it. And you're right: that carbon was once in the biosphere, millions of years ago (since oil comes from dead organic matter). There is a natural cycle which very slowly rotates carbon atoms between the biosphere and deep underground -- but the presence of that natural cycle does not prove that all carbon which was ever in the biosphere "belongs" there now. We humans can extract from the ground in a single day an amount of carbon that what would take nature many years to extract. The natural extraction is offset by an equal amount of natural sequestration -- but nature doesn't have a snowball's chance in the Arctic of ever offsetting what we're doing.
NeilFarbstein
3.3 / 5 (3) Dec 07, 2008
They found something world changing. It's a real breakthrough.
theophys
not rated yet Dec 09, 2008
What's the volume of that? Realistically the fogure touted by both the IPCC and the leading AGW skeptics is 4.4 thousand trillion liters of gas each year. That will be the volume estimate we use. Now doing some rough math we can get the volume of the atmosphere, it's about 51,000 trillion trillion liters. So human beings are releasing about 86 parts per billion CO2.

The reason why the above figure of 86 parts per billion might make you say "holy WTF his math is wrong" is because Hansen, IPCC, et al. measure the entire human CO2 budget against the troposphere alone. The lowest part of the atmosphere. CO2 emissions don't simply stay in the troposphere,


Umm...you do know that CO2 concentrates in the troposphere and that once you get into the lower stratospherre, there is very little CO2 with the concentration continuously decreasing as elevation increases, right?
Oh, and we have in fact proven that the ocean is gaining CO2 slower than the atmosphere. Measurements have been taken from both over the years and the data shows very clearly that the concentration of CO2 in the oceans, while still increasing steadily, is not increasing nearly as quickly as that of the atmosphere.

theophys
1 / 5 (2) Dec 10, 2008
1) Cyclonic activity will steadily and measurably increase.

Proven false according to observations of the past 3 years.

Uh, ballux.There has been a net increase in tornado, hurricane, cylcone, and whatever other names that I can't keep track of in the last decade.

2) Sea Ice will completely disappear by 2012.

Proven false, sea ice is currently increasing.

Extreme ultra-ballux. It's a serious problem in the arctic and the scientists in the antartic are freaking out about their sea-ice recession.

3) Sea level rise will increase leading to flooding of coastal areas by 2050.

Current satellite observations show no net change outside of standard deviation from current levels

What? Yes they do. It's not a huge rise, true, but at the rate it's going most of Florida will be the new Atlantis by 2050.

4) At 450ppm CO2 will halt photosynthesis leading to widespread plant life death.

Proven false by geological record. We wouldn't have fossil fuels to burn if this was the case, let alone be alive. The carboneferous period and proxy records show this to be an utter mistruth.

Honestly, I don't know anything about it, but I would have to agree with you. I doubt any but the most fragile plants would be screwed at 450 ppm, seeing as we are already at about 350.

The facts are there. They have been around since the 1980's and the case has been building the whole time. The fact is that global tempuratures have been on the rise for a good century now, with the occansional lapse. Natural phenomenon fail to explain the rate of increase on there own. When the greenhouse effects of CO2 are factored in, all tempuratures become accounted for. I agree with you to an extent on energy. I would much prefer to see an emphasis on fusion, solar, and wind, but this is what we've got. Hydogen cars are proven to be cleaner (note, cleaner, not cleanest) and some progress is much better than continuing to drive the mobile stinkbombs we have on the road now.
physpuppy
4 / 5 (1) Dec 25, 2008
And you're right, the oceans can absorb CO2 -- but as I'm sure you know, global warming actually *reduces* the oceans' capacity for storing CO2. ;-)

That has yet to be proven.


Um - if you accept that there is global warming and that the oceans are getting warmer also, and only considering solubility of CO2 in water, then, yes, elevated temperature = lower solubility.

Solubility of most gases go down as temperature goes up.

The trend is reversed for solubility of most solids in water though.

Now since the oceans aren't water in a beaker, there might be some other mechanism that the oceans have which balance out the solubility effect (such as converting the CO2 to other forms)

As to one poster's comment about the oceans becoming as acidic as battery acid, I could say WTF, but then again, this forum is to gain knowledge and, well, to disprove that comment, think - what you you mind more, battery acid poured on your arm or seltzer/club soda (which are super-saturated solutions of CO2)? Myself, I prefer the seltzer (with a touch of cola syrup, please) and I would be pleased to amaze everyone by drinking it!
dachpyarvile
4 / 5 (4) Dec 26, 2008
All this talk about CO2 levels being too high are a crack-up to me. Millions of years ago atmospheric CO2 was around 7,000 ppm. Today's levels are a pittance compared to that. One would need 15,000 ppm in an enclosed space to feel discomfort from CO2. From the available ice core data as well as other data available, earth never had that much CO2 in its atmosphere while life has existed on the planet.

And, to boot, plenty of corals existed then, as well as millions of ocean species now extinct.

I have been monitoring CO2 levels as well as overall temperatures for a few years now. What I am seeing is a downtrend in temperatures along with the uptrend in CO2 levels. And, let's not forget that China had the worst winter in 50 to 100 years and that it snowed again this year in Malibu, California.
dachpyarvile
3.7 / 5 (3) Dec 30, 2008
dachpyarvile - Once again, for the thousandth time, occurence of snowfalls often has very little relationship to average temperatures, more often indicating increased precipitation due to higher relative humidity, itself caused by higher average temperatures.

In general, see "Scientists have a right to expect significant basic knowledge among those who oppose their views" above.


As I said above, which comment you ignored, I am seeing a downtrend in temperatures along with a rise in CO2. It is colder this year than last in my neck of the woods and it was colder last year than the year previous. Malibu, California, has now had slushy snow for at least two or three consecutive years in a row. In all my years that sort of thing is unheard of for that area. This year, it was bad enough to shutdown roads and highways in various places in California. Las Vegas snow was a bit unexpected as well. I had to drive through it!

In my area relative humidity is about the same as it has been for the last three years. Where I am it does not factor.

We also cannot factor in average temperatures in Europe due to the fact of the anomalous situation that occurred there that raised temperatures. Europe got a rare blast of hot winds from the Sahara. Europe's temperatures skew the average results as a result.

Also see the above comment relative to albedo as it relates to average temperature. Relative albedo makes a difference.

And, let's not ignore the fact that in ancient times the levels of CO2 were significantly higher then than now. Life went on. When the temperatures fell and poisonous gases made their way into the atmosphere, mass die-offs occurred.

Personally, I would prefer to avoid another ice age. And, if we can prevent one I am all for it.
dachpyarvile
1 / 5 (1) Jan 03, 2009
Heheh! I just read an environmental study that describes the current winter as "the coldest winter of the 21st century"! Bet Al Gore is spinning on his heels trying to figure out what he is going to do if the winters keep getting colder.

Funny thing about the summary of the study, is that it states that this colder weather was expected and that it will be getting warmer come the next few years, etc...

That is a bit of a change in what so-called climatologists were claiming just a couple years ago. For them, they were expecting catastrophic winter conditions, not the gradual edging down of temperatures that has been occurring over the last few years in spite of rising CO2 levels! Now they are saying that this cold spell was expected and that it will get warmer shortly thereafter.

Yet, temperatures have fallen to below and we have dropped in average worldwide temps more than temps have risen over the last decade!

I cannot wait to see how they climb out of that one.

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