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

##### 15 July 2013
 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

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, $5kg is equivalent to petrol at something like £2-2.5 US gallon. Although presumably it would still be difficult to produce the hydrogen at home in sunny regions, unlike using electricity in batteries hydrogen could be produced in sunny places and shipped worldwide, just as oil is today. Those who are really set on using home solar arrays could have a rather more powerful battery in their fuel cell car, of perhaps 12kwh, and still do all their local running around from the plug. Since fuel cell cars already have a pretty hefty battery of around 1.5kwh and turn the wheels via an electric motor, not an ICE, the extra engineering is trivial, unlike that for petrol PHEV. That would save around 80-100kwh of battery pack per car for long range BEV travel. It would be cheaper than gasoline only 32% but way more expensive than electricity. If it is real still would not save hydrogen. Fuel Calorific value MJ/kg Efficiency Useful MJ/kg Gasoline 44.4 20% 8.88 Hydrogen 121 50% 60.50 Fuel Price Eur/kg Price Price$/gal Price €/MJ
Gasoline 1.083168083 4 0.122
Hydrogen 5 0.083

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

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.

"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.

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

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.

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?

@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.

“Route B feeds”

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.

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.

@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.

@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.

“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?

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.

Dave, I don't have any desire to go through your linked paper line by line and review it for you. It doesn't seem to tackle the question of EV or FCEV.

But perhaps there's a thing or two in it that is useful.

They present a drawing of what an 18-wheeler hydrogen fuel delivery trailer might look like.

That, of course, is part of the infrastructure we would need to build were we to use hydrogen. And infrastructure has to be paid for.

With EVs the infrastructure is largely in place. The grid is up and has plenty of spare capacity during off-peak hours. All we would need is some outlets for people who park in lots and on the street. And a few rapid charger points (see my next comment).
--

They suggest that a hydrogen fueling station would cost about the same amount as an EV charging station.

OK, but we would need enough hydrogen fueling station for every FCEV on the road while we would need only a limited number of charging stations along our major travel routes. Most people would charge at home. The infrastructure cost for hydrogen fueling stations could be 20x as much as what we would need to spend on EV charging stations.
--

Perhaps I missed it, but did they do an analysis of the percentage of starting electricity that would make it to kinetic energy with electrolysis/FCEV vs. BEVs?

There are energy losses in compressing, transporting, and converting to electricity in the fuel cell. That drives up the cost per mile.

Let me bring back this older article which could be outdated, but let's see...

The process of separating hydrogen from the water molecule, compressing and distributing is energy lossy. By one accounting if we start with 100 kWh of renewable electricity only 27 kWh actually makes it 'to the road' with a hydrogen FCEV.

Put that in the context out of the original 100 kWh about 69 kWh end up moving an EV.

http://phys.org/news85074285.html

The energy input per mile cost would be 1.9x higher for a hydrogen fuel cell vehicle if we used electricity to make hydrogen. Add on the infrastructure costs.

Now the technology in this article might lower the cost of hydrogen below that of hydrogen created by electrolysis. We'd have to look to see if it lowered it enough to overcome the other losses in the process.

And the cost of fuel would need to be significantly lower than using electricity in order to justify the capital expense and operational expenses of the hydrogen infrastructure.

Bob Wallace,

Very good and patient response. I could add that energy storage of renewable electricity generators could be tacled by different means. Hydrogen on of them and least atractive since energy storage efficiency very low. Undegraund pumped air storage could be very economic with 30% losses, hydropump storage massively used has 30% losses. Batteries could be considered as well. Within recent years less and less power storage is needed since more natural gas generation has been brought into power mix and it is very flexible and adopting to the load pattern. You do not need to store anything. Hydropower was always flexible by nature. If there would be real problem and need of additional power storage capacity may be would be reasonable to think about additional, but existing hydropump storage is underutilized.
Germany is buiding not power storages but flexible coal power plants.
Hydrogen "power storage" with 75% energy losses looks very very stupid option.

As mentioned in the article and miracles could happen this could be option of dispachable solar power generation. But power generation is comercial affair and always major issue at what price you can get power?

@Bob and Darius,
The message of this article is low-cost H2 production via dirt-cheap catalyst and one-step from solar to H2. When H2 can be produced very cheaply, it can be incorporated into waste biomass to make cheap synthetic methane or liquid hydrocarbon fuel in order to take advantage of existing infrastructure. In this way, we can overcome petroleum dependency without infrastructure change.

The efficiency difference between H2 and battery electricity is moot when synthetic hydrocarbon fuels and H2 can be produced cheaply and at large enough quantity to satisfy demand.

Renewable energy electricity is cheap, but battery storage is not. RE H2 can be stored at much lower cost than battery electricity, so, the overall costs of Battery electricity and H2-FC are comparable.

Distributed electrolysis and FC can take advantage of the waste heat of electrolysis and of FC to greatly reduce the efficiency loss. All it will take is to upgrade the existing NG piping system to become H2-compatible.

Vast quantity of H2 is currently used to make fertilizer and for petroleum refining and for organic chemistry synthesis. The technologies for safe handling and storage of H2 already exist. All it will need is to scale up for mass consumption.

Roger, it's a fairly simply issue...

Initial purchase price + operating cost. Best cost wins.

Electricity, at this point in time, is cheaper than hydrogen.

EVs are, at this point in time, are cheaper than FCEVs.

That could change, and we're watching to see if it does. But for it to change consider what it would take.

For hydrogen FCEVs to push EVs aside they have to drop their purchase price significantly below that of EVs. And since most of us expect EV batteries to drop in price quite a bit that will be hard.

For hydrogen to be a cheaper way to store energy for transportation it's going to be necessary to drastically cut the energy loss and infrastructure cost.

Moving to a hydrogen system would mean a massive infrastructure program which would essentially require us to rebuild every oil refinery, every gas station, every fuel storage depot, and every fuel delivery truck. That's an immense expenditure. And those costs have to be passed on to drivers when they purchase hydrogen.

Every FCEV is going to need a place to refuel. They can't plug in at home.

Could it be done? Possibly.

Will it be done? It would take some very heavy lifting.

Will hydrogen FCEV and hydrogen get cheap/affordable sooner than EVs? I really doubt that.

The first technology to get cheap/affordable will gain significant market share over ICEVs. ICEVs will get pushed aside because their operating expenses are too high.

For the 'first to arrive' to be pushed aside by a replacement technology the newer technology would have to be significantly cheaper to own/operate.

My guess is that EVs will get there first in terms of purchase price. Their 'fueling infrastructure' is over 90% in place and building the last <10% will be cheap.

For hydrogen FCEVs to take over the personal vehicle market they are going to have to develop extremely rapidly.

That's just my guess....

Darius, we can't continue to burn natural gas for electricity. We've got to get carbon off our grids.

Right now NG is 'acceptable' because it lets us get coal off the grid quicker. A 100% NG grid would be as disastrous as a 100% coal grid. NG releases about half as much CO2 as coal per MWh of electricity but methane leaks are an immense problem and cancel out that CO2 gain.

Because NG is dispatchable we can turn if off when wind and/or solar are available, which is quite a bit of the average 24 hour cycle. Coal and NG are about equally bad but 30% NG (plus 70% wind and solar) is immensely better than 100% coal.

Battery technology is coming on pretty quickly. Eos Systems is putting their zinc-air batteries on the ConEd grid in the next few months and claim a total cost of roughly \$0.10/kWh for <24 hour storage.

That is a NG killer. If they can store cheap off-peak power at their claimed price they will largely replace gas peakers used for daily peak demand fulfillment.

Eos is more expensive than pump-up hydro but because they can be installed so quickly and distributed around the grid, avoiding transmission costs, they will likely greatly reduce future pump-up and CAES builds.

And there are much cheaper battery technologies headed into manufacturing.

Hydrogen might compete as a grid energy storage methodology. Again, the math will decide.

"The message of this article is low-cost H2 production via dirt-cheap catalyst and one-step from solar to H2. When H2 can be produced very cheaply, it can be incorporated into waste biomass to make cheap synthetic methane or liquid hydrocarbon fuel in order to take advantage of existing infrastructure. In this way, we can overcome petroleum dependency without infrastructure change. "

I understand that. Being able to use existing distribution infrastructure would help lower the cost. But the "refinery" infrastructure would still need to be built.

Then there are the energy losses along the way, converting to liquid hydrocarbon fuel.

And then it would get used in very inefficient ICEVs which toss away about 80% of the energy in waste heat.

Solar-hydrogen for industrial feedstock. That I can see as a real possibility. As deep storage for those very infrequent times when wind and solar inputs are low, I can see that as well.

For industrial feedstock and deep grid backup solar-hydrogen would be price competing with petroleum and natural gas, not electricity.

Bob:
I assure you that I have done exactly that kind of line by line analysis of energy subjects which I am interested in, and can readily provide that level of detail in discussing the often foolish renewables schemes.

Your anecdotal approach simply amounts to pick and mix, and doesn't even get to grips with the issues.

Your notion that the costs of hydrogen infrastructure is massive and virtually rules it out is without foundation, for instance, as infrastructure does not last forever so all the oil and gas infrastructure will need replacing at some point, including the pumps on forecourts, and you need a heck of a lot less of those than you would need roadside charging points if everyone went to BEVS as a lot of cars don't have garages.

You then pick your assumptions which give you the result that BEV cars are more efficient than fuel cell cars if the power comes from electrolysis.

For starters it doesn't, as a lot of both electricity and hydrogen comes from natural gas and fossil fuels, and the two are level pegging on that.

So the ground shifts to insisting that we must allow for renewable sources, not fossil fuels.
There is no way we can actually determine what the efficiencies will be at that date in the future, as the article we are commenting on shows.

The efficiencies you reckon on simply would not apply.
They also don't apply to hydrogen from biomass, or to the same extent to high temperature electrolysis, or indeed to systems like that Audi is using so that the waste heat from hydrogen production is utilised in combined heat and power.

Your notion that renewables can form a major portion of the grid without the use of hydrogen is not one which any of the countries or major schemes is on board with, they are all looking to use hydrogen in a big way, which might give you a clue as to what is practical.

I'm not even going to start on the idea that CAES or whatever can avoid the need.
A bit of reading up would show that the few alternatives are in fact severely constrained in all sorts of ways, including in the case of CAES geography and the large amounts of natural gas that have to be used.

The simple reality is that the bright ideas have already been thought of, and if people do a quick search they would find out the reason why hydrogen is an essential component of renewable grids.

Personally nuclear works just fine with battery cars, much more efficiently than via hydrogen, but that is never, ever what battery only people want.

They have a fantasy that we can just run the lot on solar with a bit of wind.

That fantasy has no basis in technical reality.

Even the Germans who are completely nuts in their energy plans recognise that the only way they can make that work is with shed loads of hydrogen storage.

If you think differently, and that you have a cunning plan with they have not thought of, I would have thought the very least you could do is engage in substantial, detailed, point by point rebuttals.

I have for loony wind power in the UK, and solar in the UK

Gosh, Dave, I laid out very clearly, I thought, the problem with the energy loss of hydrogen as it starts with electricity input and makes it to kinetic energy. I gave you a link to an article which spells it out if you don't understand what I wrote.

And there is no way that we could possibly move from oil to hydrogen without creating a hydrogen generation and distribution system.

The electric grid is in place. 60% of all US drivers now have a place to plug in where they park. Installing parking lot/sidewalk outlets for the other 40% would not be the massive infrastructure hydrogen would require. We have available off-peak generation capacity and transmission to charge over 70% of all US cars right now and that will increase as we continue to build wind farms.

Is there something about that you don't understand?

@Bob,
A hydrogen generation and distribution system will be built gradually as H2 will gradually overtake petroleum as transportation fuel and NG for home heating in the form of FC-CHP. The cost will come down with experience and with mass production. The cost of H2 infrastructure will be financed by private money and will be amortized gradually as the consumers will pay for the new form of energy, but at no higher cost than what they are paying now for fossil-fuel energy, due to the greater efficiency of H2 utilization in FCV's and in home FC-CHP.

BEV's and PHEV's are also very valuable way to displace petroleum demand, but cannot replace H2 infrastructure, and Davemart has discussed at length.

Every FCEV is going to need a place to refuel. They can't plug in at home.

Why not? First of all, a Fuel Cell Electric Vehicle is an electric vehicle: It will have a battery pack AND a fuel cell. Think of it as an EREV with a FC instead of an ICE. At the very least you should be able to plug in the battery pack.

Second, people are doing home hydrogen generation;

http://www.geek.com/chips/zeep24-powers-your-house-with-hydrogen-produced-using-solar-power-1419867/
http://switch2hydrogen.com/

How much it will cost depends on how big you want to go - this guy went VERY big;