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EPFL/Technion team develops “champion” nanostructures for efficient solar water-splitting to produce hydrogen

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Hydrogen bubbles as they appear in a photoelectrochemical cell. © LPI / EPFL. Click to enlarge.

Researchers from EPFL in Switzerland and Technion-Israel Institue of Technology have developed nanoparticle-based α-Fe2O3 (hematite) electrodes that achieve the highest photocurrent of any metal oxide photoanode for photoelectrochemical water-splitting under 100 mW cm−2 air mass, 1.5 global sunlight. A paper on their work is published in the journal Nature Materials.

With current methods, in which a conventional photovoltaic cell is coupled to an electrolyzer to produce hydrogen, the cost to produce hydrogen from water using the sun is around €15 per kilo at its cheapest, said research leader Dr. Michael Grätzel, Director of the Laboratory of Photonics and Interfaces (LPI) at EPFL and inventor of dye-sensitized photoelectrochemical cells. “We’re aiming at a €5 charge per kilo,” he said.

Batteries, fuel cells and solar-energy conversion devices have emerged as a class of important technologies that increasingly rely on electrodes derived from nanoparticles. These nanoparticle-based materials provide a unique challenge in assessing structure–property relationships because of the disordered arrangement of nanocrystals that results when nanoparticles collide and aggregate. The morphological evolution that follows aggregation further obscures the influence of particle size, shape and interfacial characteristics in defining the physical properties of these materials.

For the nanoparticle-based electrodes used in solar energy conversion, structural defects such as grain boundaries define pathways for charge transport by creating potential barriers and by promoting recombination. Owing to the complexity of these materials, within a single electrode there may exist a small proportion of champion nanostructures—by analogy with champion solar cells, these are nanostructures that provide the highest solar conversion efficiencies—that contribute most of the electrode’s photocurrent. Further improvement of device performance requires an analytical approach that identifies these champion nanostructures, quantitatively relating their microstructural features to their charge transport characteristics.

—Warren et al.

The team, led by Dr. Grätzel and Prof. Avner Rothschild at Technion in Israel, developed an approach for correlating the spatial distribution of crystalline and current-carrying domains in entire nanoparticle aggregates. In correlating structure and charge transport with nanometer resolution across micrometer-scale distances, they identified the existence of these “champion” nanoparticle aggregates that are most responsible for the high photoelectrochemical activity of the electrodes.

Today we have just reached an important milestone on the path that will lead us forward to profitable industrial applications.

—Michael Grätzel

The whole point of our approach is to use an exceptionally abundant, stable and cheap material: rust.

—Scott C. Warren, first author, now at the University of North Carolina at Chapel Hill

At the end of last year, Kevin Sivula, one of the collaborators at the LPI laboratory, presented a prototype electrode based on the principle. Its efficiency was such that gas bubbles emerged as soon as it was under a light stimulus.

By using transmission electron microscopy (TEM) techniques, researchers were able to precisely characterize the movement of the electrons through the cauliflower-looking nanostructures forming the iron oxide particles, laid on electrodes during the manufacturing process.

By comparing several electrodes, whose manufacturing method is now mastered, scientists were able to identify the “champion” structure. A 10x10 cm prototype has been produced and its effectiveness is in line with expectations, the researchers said. The next step will be the development of the industrial process to large-scale manufacturing. A European funding and the Swiss federal government could provide support for this last part.

The long-term goal is to produce hydrogen in an environmentally friendly and especially competitive way.

Resources

  • Scott C. Warren, Kislon Voïtchovsky, Hen Dotan, Celine M. Leroy, Maurin Cornuz, Francesco Stellacci, Cécile Hébert, Avner Rothschild and Michael Grätzel (2013) Identifying champion nanostructures for solar water-splitting. Nature Materials doi: 10.1038/nmat3684

Comments

Davemart

It will be interesting to see how many, if any, opponents of the use of hydrogen in cars will change their tune if this pans out.

Given the greater efficiency of fuel cells compared to ICE, $5kg is equivalent to petrol at something like £2-2.5 US gallon.

Although presumably it would still be difficult to produce the hydrogen at home in sunny regions, unlike using electricity in batteries hydrogen could be produced in sunny places and shipped worldwide, just as oil is today.

Those who are really set on using home solar arrays could have a rather more powerful battery in their fuel cell car, of perhaps 12kwh, and still do all their local running around from the plug.

Since fuel cell cars already have a pretty hefty battery of around 1.5kwh and turn the wheels via an electric motor, not an ICE, the extra engineering is trivial, unlike that for petrol PHEV.

That would save around 80-100kwh of battery pack per car for long range BEV travel.

Darius

It would be cheaper than gasoline only 32% but way more expensive than electricity. If it is real still would not save hydrogen.

Fuel Calorific value MJ/kg Efficiency Useful MJ/kg
Gasoline 44.4 20% 8.88
Hydrogen 121 50% 60.50

Fuel Price Eur/kg Price Price $/gal Price €/MJ
Gasoline 1.083168083 4 0.122
Hydrogen 5 0.083

kelly

A major reduction in the cost of storing solar energy is always welcome.

Bob Wallace

Dave, at least on my part it is not an opposition to using hydrogen in vehicles. It's economics.

I am 100% for any technology that makes it possible to get away from fossil fuels. Hydrogen math hasn't worked.

If this technology can produce cheap hydrogen in volume then the math has changed some. The next question would be whether it has changed enough.

Producing hydrogen is only one place where energy loss has made hydrogen a less viable technology. That hydrogen still needs to be compressed, distributed and turned into kinetic energy.

Kit P

"It's economics."

So BS Bob is now against all forms of solar especially solar charging of BEV.

Of course it does not matter how cheap hydrogen is as long as it has the physical property of detonation. Davemart does not understand the difference between being in the presence of 1 ppb PAH and a hydrogen detonation.

Dead compared to an insignificant risk over a lifetime.

Davemart

Bob:

I've gone through the math on the energy efficiency and cost of hydrogen versus batteries umpteen times on this blog, and heard nothing numeric in response.

If you wish to claim that the math doesn't work, here is one of the umpteen studies on the issue.
I await your detailed point by point rebuttal showing all numbers and calculations.

http://www.hydrogen.energy.gov/pdfs/progress12/i_0_satyapal_2012.pdf

Davemart

Darius:
If you are happy like me to provide most of our power by nuclear, then batteries are probably a more efficient solution, although you are still carrying around ~1000lbs of battery.

If, OTOH, you support renewables instead or as well as nuclear, then no one at all has figured out how to store the electricity, so the comparison you wish to make just doesn't work.

Aside from Germany, and everyone else who is going for renewables playing a big part in the grid relying heavily on hydrogen to make it work at all, here is energy rich Norway, which although it has far greater electricity storage per capita than almost everywhere else due to their small population and extensive hydropower resources, still sees hydrogen as vital:
http://www.fuelcelltoday.com/media/1838763/fuel_cells_and_hydrogen_in_norway.pdf

If you reckon they are missing how to run things on electricity without recourse to hydrogen, please rebut their own studies, and show how you are going to manage things in detail and with numbers.

This is not just me being awkward.
I am deeply critical of the consensus in favour of renewables, but my critique is always in detail and by appeal to the actual numbers.

GreenPlease

To me, an obvious application is a cheap hydrogen source for an FT fuels plant. The huge capital investment required for an FT plant doesn't seem so risky when your price of hydrogen is fixed (vs the variable nature of NG).

Split water. Siphon H to Route A, siphon O to route B. Route B feeds a coal fired power plant (essentially) which partially oxidizes C to CO which gets siphoned to Route C. Route A and C converge in the presence of a catalyst and, boom, you have methanol etc.

The question, then, is how durable is this photo-catalyst?

Davemart

@Kit:
You are confusing hydrogen with the methane in your beloved coalmines, which continues to exact a high toll in mortality.

You had better write to Daimler, and tell them that they have it all wrong, and that the umpteen test vehicles they have driven for years have in fact already exploded, likewise the Honda Clarity FX car, and the Hyundai FCEVs in production.

The decades of experience piping and transporting hydrogen was obviously all a mistake, as we have your word for it.

I don't mind your being an ignorant fool, but it is tedious when you keep sharing it.

Kit P

“Route B feeds”

@Greenplease

Do you have any experience with oxygen as an industrial gas?

There are those who always come up with ways for others to do things without considering the safety of those who actually do the work.

“You had better write to Daimler, and tell them ”

@Davemart

When they try bring hydrogen to my town I will explain why I will not let them do it.

“The decades of experience piping and transporting hydrogen was obviously all a mistake, as we have your word for it. ”

Actually I do have decades of experience doing it in an industrial setting. Did it safely. However there are numerous failures resulting in deaths.

Making hydrogen ubiquitous in our communities is just not going to happen. It is not a battle that I will ever have to fight since since HFCV will never be more than an very expensive concept.

Alain

Even if we never use H2 directly in our cars (which I doubt), there is enormous H2 consumption in industry. If we could even start to replace this fossil-sourced H2 by solar H2,it would already be an enormous achievement.
Whether you like coal-to-liquid, biomass-to-liquid, CO2-to-liquid, garbage-to-liquid, hythane, H2 fuelcells, H2 ICE,...

However, although I wish them the best, I doubt they will ever compete with direct electric. solar and wind price is falling dramatically and will continue to do so. The decoupling of producing electricity (deserts, open sea, my roof) and producing H2 (industrial plants, my garage, gas stations) has huge advantages.
In addition, photovoltaics can be used to produce electricity whenever this is needed most, and spare (cheap) electrons can be used to produce H2 for later use. Separating again the photovoltaic cells and direct watersplitters ruin this advantage.

kelly

@Davemart, "[Kit P] I don't mind your being an ignorant fool, but it is tedious when you keep sharing it."

Thanks for this comment, disregard if gratitude isn't appropriate.

Davemart

@kelly:

I may agree with Kit on nuclear, but the way he dismisses the very real health concerns of fossil fuels and ignores the collective opinion of the medical profession is crazy.

Although I try to deal with argument rather than persons, I would be tempted to consider him a shill, except that I can't imagine that anyone would pay someone to write such baseless nonsense.

However, they paid for equally dumb arguments to be made in favour of the health giving effects of tobacco for years, so I suppose the notion can't be dismissed out of hand.

In any event, although at times with others on here the debate may become lively and somewhat sharp, Kit I simply dismiss out of hand, and have no interest whatsoever in his comments, which as far as I am concerned have no connection with reality or respect for the data.

Kit P

“medical profession is crazy. ”

I have a great deal of respect for the medical profession. When they tell me that levels of pollution above a certain level are harmful I listen. Then I check to see what the levels are where I live. Where I live has good air quality.

What is the problem?

Roger Pham

The truth is that there now exist many ways of electrolysis of water without using platinum, making electrolyzers inexpensive.

Still, being able to get H2 directly from solar energy all in one step will cut down on the two-step method of H2 production from solar PV and then to electrolyzer. Wondering what is the energy yield per sq meter vs. solar PV? The H2 produced from this is extremely valuable as organic chemistry synthetic feedstock, to produce refinable liquid hydrocarbon via flash pyrolysis of waste biomass all in one step with high efficiency and low cost. The issue of H2 storage, transportation, compression and distribution will be moot once we will produce renewable hydrocarbon fuels economically from waste biomass and solar, wind and nuclear energy.

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