Stanford team devises a better solar-powered water splitter (w/ video)

Jun 21, 2011 by Andrew Myers

(PhysOrg.com) -- The process of splitting water into pure oxygen and clean-burning hydrogen fuel has long been the Holy Grail for clean-energy advocates as a method of large-scale energy storage, but the idea faces technical challenges. Stanford researchers may have solved one of the most important ones.

Solar energy is fine when the sun is shining. But what about at night or when it is cloudy? To be truly useful, sunshine must be converted to a form of energy that can be stored for use when the sun is hiding.

The notion of using sunshine to split water into oxygen and storable has been championed by clean-energy advocates for decades, but stubborn challenges have prevented adoption of an otherwise promising technology.

A team of Stanford researchers may have solved one of the most vexing scientific details blocking us from such a clean-energy future.

The team, led by materials science engineer Paul McIntyre and chemist Christopher Chidsey, has devised a robust silicon-based solar electrode that shows remarkable endurance in the highly corrosive environment inherent in the process of .

They revealed their progress in a recent paper published in the journal .

Conceptually, splitting water could not be simpler. Scientists have long known that applying a voltage across two electrodes submerged in water splits the into their component elements, oxygen and hydrogen.

From an environmental standpoint, the process is a dream: an whose only requirements are water and electricity and whose only byproducts are pure oxygen and hydrogen, a clean-burning fuel applicable in a promising new class of renewable energy applications. In fact, hydrogen is the cleanest burning known.

Practical challenges

"In theory, is a clean and efficient mechanism. Unfortunately, solving one problem creates another," said McIntyre, associate professor of materials science and engineering. "The most abundant solar electrodes we have today are made of silicon, a material that corrodes and fails almost immediately when exposed to oxygen, one of the byproducts of the reaction."

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An interdisciplinary group of Stanford researchers from the engineering and chemistry departments have developed a new way to protect silicon semiconductors during water-splitting reactions. Scientists say the breakthrough may hold the key to storing solar energy.

This particular problem has vexed researchers since at least the 1970s. Many had given up, but McIntyre and Chidsey have devised a clever solution. They coated their silicon electrodes with a protective, ultra-thin layer of titanium dioxide.

"Titanium dioxide is perfect for this application," explained McIntyre. "It is both transparent to light and it can be efficient for transferring electricity, all while protecting the silicon from corrosion."

Sunlight travels through the protective titanium dioxide into the photosensitive silicon, which produces a flow of electrons that travels through the electrochemical cell into the water, splitting the hydrogen from the oxygen. The hydrogen gas can be stored and then, when the sun is not shining, the process can be reversed, reuniting hydrogen and oxygen back into water to produce electricity.

Decades of dead ends

Other researchers had attempted to protect the electron-producing silicon electrodes. Some tried other materials, which failed for reasons of performance or durability. Some had even tried titanium dioxide, but those efforts also fell short. Their layers were either materially flawed, allowing oxygen to seep through and corrode the semiconductor, or too thick to be electrically conductive. 

Yi Wei Chen and Jonathan Prange, the lead doctoral students on the McIntyre-Chidsey team, discovered that the key to the titanium dioxide's protectiveness is achieving a very thin, yet high quality layer of material. They found that a layer just two nanometers thick was sufficient so long as it was free of the pinholes and cracks that doomed earlier titanium dioxide experiments.

With their electrodes successfully shielded from corrosion, the researchers revealed yet one more engineering ace in the hole, adding a third layer of ultra-thin iridium, a catalyst, atop the titanium dioxide. Iridium boosts the rate of the splitting reaction and improves performance of the system.

Broader applications

In side-by-side durability experiments, the researchers put their creation to the test. Control samples without the protective layer corroded and failed in less than a half-hour, while those with the lasted the full duration of the test, eight hours without apparent corrosion or loss of efficiency.

The authors pointed out that their approach is general enough to work on other semiconductor substrates and to integrate other catalysts, allowing for fine-tuning of electrodes to maximize performance. Likewise, atomic layer deposition, the technique that allowed such fine and flawless layering, is in wide application in the semiconductor industry today. It should, therefore, lend itself to application on a large scale. Lastly, the results were achieved without exploring the use of other efficiency-enhancing techniques, such as surface texturing, which could further improve performance.

"We are excited about the possibilities of this technology," said McIntyre, "as much for the electrode itself, as for the process used to create it."

Their success might just push a promising technology one step closer to practical application and the world one step closer to a clean-energy future.

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wealthychef
1 / 5 (1) Jun 21, 2011
Eight hours is not 8,000 hours. How long will this technology last in real-world applications? Clearly they are optimistic. And if this succeeds in "pushing a promising technology one step closer to practical application," what are the other steps that need to be taken before we get clean energy at a decent price?
Sanescience
1 / 5 (1) Jun 21, 2011
In fact, hydrogen is the cleanest burning chemical fuel known.

In theory, water splitting is a clean and efficient energy storage mechanism.


Hydrogen is a terrible medium for storing or transporting energy. It generally requires heavy equipment, high pressures, and cryogenics that are expensive to maintain. The "engines" that would use it would be beyond any average mechanic let alone the public to maintain.

Non-food competing GM crops and algae bioreactors can produce enough biodiesel to put a pretty big dent in transportation fuel consumption. Biodiesel is clean burning, easy to transport and store. Is biodegradable, carbon neutral, does not readily burn in the open air, and has higher energy density than gas. Cars already using it have better millage than hybrids.

First chain of stations that sells an American Brand biodiesel will be able to sell it at a higher price than gas.
dirk_bruere
not rated yet Jun 21, 2011
Wow! 50% efficient!
Or is it 0.01% efficient?
We don't have a clue, do we?
Shelgeyr
2 / 5 (8) Jun 21, 2011
...hydrogen is the cleanest burning chemical fuel known.


How can they say that??? Don't they know that water vapor is the biggest greenhouse gas there is, responsible for between an estimated 36 to 72% of the "greenhouse effect"? Heck, even old dreaded CO2 only contributes between 9 and 26% - its estimated TOP END is ten percentage points below the postulated lower end of water vapor's nefarious effect!

This "solar-powered water splitter" is kind of cool and all, but Sanescience is right - Hydrogen is a pain in the neck to use (I'm paraphrasing).

From Wikipedia: Liquid hydrogen has less energy density by volume than hydrocarbon fuels such as gasoline by approximately a factor of four. This highlights the density problem for pure hydrogen: there is actually about 64% more hydrogen in a liter of gasoline (116 grams) than there is in a liter of pure liquid hydrogen (71 grams). The carbon in the gasoline also contributes to the energy of combustion.

Go gasoline!
IlliterateGraduate
5 / 5 (2) Jun 21, 2011
So many negative comments...

The only way we are going to achieve a sustainable energy future is by cultivating any and all energy possibilities. The idea that there is going to be one solution to the energy crisis is preposterous. Wind/wave/biofuel/solar/hydrogen will all have to be improved and used and all seem to be cleaner and pose less danger than nuclear, coal, or oil.

Stop complaining and start contributing.
Deesky
5 / 5 (2) Jun 21, 2011
Hydrogen is a terrible medium for storing or transporting energy. It generally requires heavy equipment, high pressures, and cryogenics that are expensive to maintain. The "engines" that would use it would be beyond any average mechanic let alone the public to maintain.

That's generally true and is why H will never be used in personal transportation (either in combustion engines or fuel cells).

However, there is an application where the drawbacks aren't so significant - power generation. If a power plant makes its own H and combusts it to generate power, then you don't need to transport the stuff around and you can contain any risks locally. The electricity produced can be used to power electric vehicles (rather than H itself).

But questions still need to be answered before this becomes reality: cost/economics, scale, longevity, etc.
blazingspark
1 / 5 (1) Jun 22, 2011
This is good news! Once we resolve hydrogen storage issues every household could potentially become a closed system. Maybe have the electric grid as a backup and sell your excess power to big business.
kaasinees
1 / 5 (1) Jun 22, 2011
Asuming its 50% efficient, which is probally optimistic in the slightest. And asuming burning H and O is 50% efficient. And asuming getting energy from that is 50% efficient...

Well we are at the efficiency of PV now. Or am i missing something?
Deesky
5 / 5 (1) Jun 22, 2011
Well we are at the efficiency of PV now. Or am i missing something?

What you're missing is that H is an energy carrier or a storage medium, if you will, which means you can make use of the energy whenever it's needed. With PV, you either use the energy as it's produced or lose it.
Eikka
not rated yet Jun 22, 2011
You need lots of hydrogen anyways, becuse we need to synthesize chemicals such as ammonia (NH3) which currently gets the hydrogen it needs from splitting natural gas.

Otherwise we have no fertilizers, and no food.

Approximately 83% (as of 2004) of ammonia is used as fertilizers either as its salts or as solutions. Consuming more than 1% of all man-made power, the production of ammonia is a significant component of the world energy budget.
kaasinees
1 / 5 (1) Jun 23, 2011
Eikka that makes sense, thank you.
I think most scientist would agree that using hydrogen for fuel is a bit of a bad idea, but that was a good point of doing this kind of research.
neiorah
not rated yet Jun 23, 2011
If those who complain have a better way to do then fine but if not them shut the heck up.
StandingBear
1 / 5 (2) Jun 26, 2011
There you have it. But the fly in the ointment is the Iridium. You need it! It is very rare! ON EARTH. Oh!, but in space it is more plentiful on asteroids. So we will need the solar electric or nuclear propulsion to go to the asteroid belts to mine this stuff to help make our planet go.....or we can all be forcibly converted to Islamics in order to qualify to continue to be able to import ...oil. Bottom line, to get the Iridium and avoid being thrust back into the dark ages, we will have to develope cheaper space travel....nuclear main takeoff propulsion....or fusion propulsion which is far cleaner. Personally I favor fusion. We have some good designs..only thing stopping us is the oil lobby and their thirst for profits and our blood.
FrankHerbert
1 / 5 (5) Jun 26, 2011
StandingBear, your Islamophobia is rather pathetic and borderline psychotic.

And what is it with conservatives omitting 'ic' from the end of words that need it and adding 'ic' to the end of words that don't? This seems to be very consistent, like conspiracy theorists adding spaces before their commas , like that.
Kozmik_Ray
not rated yet Jun 28, 2011
Ok,I've been reading hear at this site for a long time and I must say the flaming and off topic comments or general lack of focus can be a bit discouraging. So I had to finally register and chime in. Now, technology like any other proceeds in steps or stages. Right? I have been hoping for these days since reading OMNI mag as a kid(10-ish). The problem with any carbon based fuel seems to be the method of harnessing the energy, not the fuel itself. i.e. ICE tech, slowly getting better. Biodiesel holds much promise. Comments welcome, thanks.
Kozmik_Ray
not rated yet Jun 28, 2011
Sorry if I sound like I am merely stating the obvious. More like I had to get that off my chest. And the iridium issue could spark off private asteroid mining ventures. Kinda like how privatized space venture are mostly somewhat tourist based for now,aside frome SpaceX,but they may inspire the paradigm shift. Are they listening??
Kozmik_Ray
not rated yet Jun 28, 2011
I would love to start a local Physorg type of user group. I live in PDX and we have the first of solar battery charger for EV's in the country, maybe N.A. amongst other Green Firsts here. Things are happening! Gotta get the Donald Trumps off their a**es and forgo stupid tv show garbage and make a real contribution to world society.
saintronmcg
not rated yet Jun 28, 2011
My 98 Mitsubishi Mirage 1500 cc AT 2 door no frills. Runs just fine on west coast sea water. On demand,stored and maintained 55 PSI. 10 gal. storage tank in trunk, all hydro. hoses .50" I.D. rated 50k PSI. Splitter and storage tank encased in steel angle iron and wire mesh shroud for containment. Safety pop off valves x 4 spring loaded and vented to rear exterior. 2 x 2", and 2 x 3" Pop off at 75 PSI. Using stainless steel plates inside 125 psi rated 50 gal. swimming pool stainless filtration tank. Storage is ten gal. 125 psi rated air tank. Inert gases are cleaned via stand alone distilled water temp. controlled thru a stainless tranny cooler. Electrolysis in brute force mode enabled by additional high amp alternator feeding 2, 12 volt lead acid deep cycle battery's. Original fuel tank removed. Original fuel injection system disabled. ECM modded. Timing adjustable at the dashboard. Potentiometer. Seawater temp maintained at 170 F. Stainless radiator. 1 valve at plenum injects hho.

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