## EPFL team develops low-cost water splitting cell with solar-to-hydrogen efficiency of 12.3%

##### 26 September 2014

A team led by Dr. Michael Grätzel at EPFL (Ecole Polytechnique Fédérale de Lausanne) in Switzerland has developed a highly efficient and low-cost water-splitting cell combining an advanced perovskite tandem solar cell and a bi-functional Earth-abundant catalyst.

The combination of the two delivers a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. (Currently, perovskite instability limits the cell lifetime.) Their paper is published in the journal Science. In a companion Perspective in the journal, Dr. Thomas Hamann of Michigan State University, who was not involved with the study, called Grätzel’s team’s work “an important step towards achieving [the] goal” of quickly developing alternative sources of energy that can replace fossil fuels.

 Science published the latest developments in Michael Grätzel's laboratory at EPFL in the field of hydrogen production from water. By combining a pair of perovskite solar cells and low price electrodes without using rare metals, scientists have obtained a 12.3% conversion efficiency from solar energy to hydrogen, a record with earth-abundant materials. Jingshan Luo, post-doctoral researcher, explains how. Credit: EPFL

Hydrogen, which is the simplest form of energy carrier, can be generated renewably with solar energy through photoelectrochemical water splitting or by photovoltaic (PV)–driven electrolysis. Intensive research has been conducted in the past several decades to develop efficient photoelectrodes, catalysts, and device architectures for solar hydrogen generation. However, it still remains a great challenge to develop solar water-splitting systems that are both low-cost and efficient enough to generate fuel at a price that is competitive with fossil fuels.

Splitting water requires an applied voltage of at least 1.23 V to provide the thermodynamic driving force. Because of the practical overpotentials associated with the reaction kinetics, a substantially larger voltage is generally required, and commercial electrolysers typically operate at a voltage of 1.8 to 2.0 V. This complicates PV-driven electrolysis using conventional solar cells—such as Si, thin-film copper indium gallium selenide (CIGS), and cadmium telluride (CdTe)—because of their incompatibly low open-circuit voltages. To drive electrolysis with these conventional devices, three to four cells must be connected in series or a DC–DC power converter must be used in order to achieve reasonable efficiency. … In contrast, perovskite solar cells have achieved open-circuit voltages of at least 0.9 V and up to 1.5 V according to recent reports, which is sufficient for efficient water splitting by connecting just two in series.

—Luo et al.

 “This is the first time we have been able to get hydrogen through electrolysis with only two cells!”—Jingshan Luo

The EPFL team used a perovskite solar cell based on CH3NH3PbI3. The cell has a short-circuit photocurrent density, open-circuit voltage, and fill factor of 21.3 mA cm−2, 1.06 V, and 0.76, respectively, yielding a solar-to-electric power conversion efficiency (PCE) of 17.3%.

To overcome the large water-splitting overpotentials that are typically required to generate H2 and O2 at a practical rate, the EPFL researchers looked to implement efficient electrocatalysts.

They sought to avoid conventional expensive noble metals of low abundance, such as Pt, RuO2, and IrO2. For sustained overall water splitting, the catalysts for the H2 evolution reaction (HER) and O2 evolution reaction (OER) must be operated in the same electrolyte—which should be either strongly acidic or alkaline to minimize overpotentials, they noted. This requirement is a challenge for most of the Earth-abundant catalysts because a highly active catalyst in acidic electrolyte may not be active or even stable in basic electrolyte.

Thus, it is crucial to develop a bifunctional catalyst that has high activity toward both the HER and OER in the same electrolyte (either strongly acidic or strongly basic). Moreover, the use of a bifunctional catalyst simplifies the system, lowering the manufacturing cost and thus the cost of the resulting hydrogen.

—Luo et al.

To solve this, they incorporated iron (Fe) into Ni(OH)2 to form NiFe layered double hydroxides (LDHs). The resulting catalyst electrode exhibited high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte.

 Combination of the perovskite tandem cell with NiFe DLH/Ni foam electrodes for water splitting. (A) Schematic diagram of the water-splitting device. (B) A generalized energy schematic of the perovskite tandem cell for water splitting. Luo et al. Click to enlarge.

Overall, the NiFe LDH/Ni foam electrode shows nearly the same performance as the Pt/Ni foam electrode, with 10 mA cm−2 water-splitting current reached by applying just 1.7 V across the electrodes. To confirm the bifunctional activity of the NiFe LDH/Ni foam electrodes, the evolved gaseous products were quantified by means of gas chromatography. We confirmed quantitative Faradaic gas evolution at the predicted 2:1 ratio for hydrogen and oxygen, within experimental error. The exceptional bifunctionality, high activity, and low cost of the NiFe LDH/Ni foam electrode make it highly competitive for potential large-scale industrial applications.

—Luo et al.

Commenting on the EPFL team’s work, Dr. Hamann noted that:

While the 12% water-splitting efficiency reported is already exceptional, there are several paths to improvement. Use of a single band-gap material in a tandem configuration is not ideal, and combining a perovskite cell with a smaller band-gap semiconductor such as silicon could produce over 20% STH efficiencies. Some loss in available photovoltage by substituting a lower-voltage silicon cell for one of the high-voltage perovskite cells in order to increase the photocurrent may be compensated by the use of a better HER catalyst that requires a smaller overpotential. The NiFe LDH catalyst is also opaque and not amenable to an integrated photoelectrochemical system. It is not yet clear if alternative transparent catalysts are absolutely necessary or if the separated PV/electrolyzer configuration used here will ultimately be viable.

Resources

• Jingshan Luo, Jeong-Hyeok Im, Matthew T. Mayer, Marcel Schreier, Mohammad Khaja Nazeeruddin, Nam-Gyu Park, S. David Tilley, Hong Jin Fan, and Michael Grätzel (2014) “Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts” Science 345 (6204), 1593-1596 doi: 10.1126/science.1258307

• Thomas Hamann (2014) “Perovskites take lead in solar hydrogen race” Science 345 (6204), 1566-1567 doi: 0.1126/science.1260051

### Comments

Many thanks for the best write up on this exciting technology I have seen so far, Mike!

I think that they just sell this patent to big oil for a quick profit and we won't see it on the market in the next 50 years. They say something great to sell it and give it a plus-value but they say that it is not ready because it was sold to big oil that want to flush it to the trash while impeding anyone to commercialize it.

Im sure that big oil own 200 or more patents in the hydrogen technology, all not commercialize.

Don't give up yet, gor!
This won't be ready by your target date of 2022 for your new car, but there is no reason to assume it won't come online at some point, as the bridge is no greater than it was for any sort of solar cell 15-20 years ago providing economic power.

In the meantime the DOE reckons that hydrogen from natural gas can be done for $2-4gge plus taxes by 2020. Since the Toyota FCEV Highlander got 68 mpgge, and the hybrid Toyota Highlander is rated at 24-28 mpg, then the fuel cell version is around two and a half times as efficient per gge, as reforming losses are already accounted for in the DOE figures. So that is pretty much like$1.50-2.00 gasoline for equivalent miles!

Its not clear how much the car will cost though, so don't get your hopes up unduly, but don't despair either.

Agree, DM, GCC has the best technical coverage on Green Techs. Now that the cost of solar and wind energy is low and is getting lower, a low-cost electrolyzer system like that is shown here will move us a step closer to an H2 economy while phasing out fossil fuels.

@gor,
Eventually, Big Oil will become Big Hydrogen because oil and gas wells will run dry, and H2 is the lowest-cost and most efficient synthetic fuel that one can make from non-fossil energy sources . However, if H2 will become profitable sooner, new investments in fossil fuels will stop and will go to investments in H2 and RE. It is just a matter of time! My crystal ball now says that new investments in oil, gas, and coal should now stop, to be switched over to RE, H2 and battery.

H2 is so simple to synthesize from non-fossil fuel sources and can be made right at the point of consumption, thus saving a lot of expenses and energy in transporting the oil and gas long distance from the well, and then considerable cost in oil refining and Nat Gas purification, and then transporting the refined fossil fuels to the point of consumption. That is why oil will remain expensive while H2 will cost very little to make.

DM > In the meantime the DOE reckons that hydrogen from natural gas can be done for $2-4gge plus taxes by 2020. Not including carbon sequestration, which we will dearly need by then, if current CO2 levels are any indication. Another six years, batteries will likely be half the current price, and all indications are that 200+ mile range EVs will be available from several manufacturers at reasonable prices. How$4 gge H2 will compete with $1 gge or cheaper EVs will be a really interesting contest. Roger, your ability to believe that H2 will be cost-effectively produced from anything other than natural gas is an impressive feat of mental gymnastics. I say that with genuine awe. At least Davemart is honest about where the H2 will be coming from, which I respect. @eci: You are trying to hard to prove a case, which makes it difficult to judge fairly. That is apparent, as you chose the highest price the DOE gave,$4gge, when if you were trying to be even handed you would surely have chosen at least the median price, $3gg plus taxes. Even the highest price though, with the far more efficient efficient use of fuel by fuel cells, means the cheapest fuel in a generation. You simply ignore that if there is a problem competing with the still cheaper cost per mile of EV's, then building FCEVs as PHEVs as VW plant to would obviate that for any day to day travel, whilst providing long distance travel at a fraction of ICE fuel prices, whilst the needed infrastructure roll out would be minimal as it would only need to service major highways etc. As for: 'At least Davemart is honest about where the H2 will be coming from' that is a gross misunderstanding of what I posted. Possibly you have not had time to read the link I posted, but it is clear from that that although hydrogen from NG is the first one to be competitive, there are a whole host of alternatives coming down the track with the first being hydrogen from biomass, which have at least as much likelihood of being cost competitive as your notion of large decreases in battery price. The last post I made was getting rather long, so I will look at the question of CO2 emissions here. For a start hydrogen from natural gas, without considering the host of other technologies coming along very nicely with far lower CO2, is way lower in CO2 than the present use of petrol, so you are talking about a very large decrease even pending lower CO2 technologies. You then talk as though EVs were running on solar. They aren't. A heck of a lot of their power comes from coal, which is way more CO2 heavy than NG. Now maybe one day hugely more of the grid will come from solar, up from the present less than 1%, and maybe batteries will store it overnight. In that case it is odd to be talking a lot about your '$1gge' with nary a mention of the capital costs of batteries here, there and everywhere.

They won't do a thing to solve annual solar variation anyway, which hydrogen does.

Its not surprising that you come down heavily on one side when all your assumptions favour that.

I don't know how things will pan out, and neither does the DOE, as what happens depends on how fast the various technologies progress, and it is not a one horse race as you suggest.

Even in terms of CO2 emissions, let alone system cost, fuel cells have a lot going for them.

That is aside from the very real possibility of this or several other technologies being able to produce hydrogen direct from sunshine.

Battery only folk like to tell others not to bet against Musk.

If we are talking energy from solar, it is also unwise to bet against Dr Gratzel.

Here is the DOE link that is under discussion:
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/hptt_roadmap_june2013.pdf

Note that in Table 1.3 page 14 there are a variety of low carbon methods which, although above the DOE target, are still likely to be a lot cheaper than petrol, some of them by 2015, which means that since the report is June 2013 they must be almost there.

Note in particular central production of hydrogen from biomass, as $2.10 gge, which even after distribution costs seems likely to still be below the$4gge that evi picked out from the DOE's $2-4gge range ex tax for distributed NG reformation. The suggested timeline of$2gge for 2020 for centralised production of hydrogen from green electricity is also interesting.

I did indeed read the study, and thanked you for posting it in the recent ORNL Stufpdy re naturalmGas link.

I won't rehash the whole post but its worth noting for this discussion that the report cited unambiguously states:

"With the exception of natural gas reforming, all hydrogen production technologies discussed in this roadmap require significant advancements and additional development prior to commercial use."

H2 from renewables appears to be considerably down the road. Cost competitive H2 from renewables much further. A good thorough read of that EERE study reveal just how far. It's not very encouraging.

Thanks again for posting the link. it's always interesting, if not convincing.

This story describes a method that does not use an expensive platinum catalyst, that is the "take away" point. If they can make this inexpensively, the rest will be land usage.

It's an exciting development. But the technology currently has a ver serious shortcoming, noted in the article: "Currently, perovskite instability limits the cell lifetime."

It's a very serious limitation, one that makes the technology not commercially viable until its overcome. I hope they do overcome it. But it's very premature to hail the dawn of the Hydrogen economy.

@eci:

The hydrogen economy can be got off the ground and running just fine with reformed natural gas, which is no more carbon intensive than electricity for battery cars is at the moment.

There are good prospects of reducing the carbon intensity of the electricity for BEVs, but equally good ones of reducingn those of hyrogen, and much, much better prospects of its being usable winter and summer in areas north of San Diego, and so not needing massive fossil fuel 'back up'

Dr Gratzel with his dye sensitive solar cell is well used to the problems of increasing durability, but the hydrogen economy in no way has to wait on his success, or those of the half a dozen other paths for direct solar to hydrogen.

Simple low cost (low efficiency) Solar to H2 converts could become game changers in sunny underdeveloped areas.

Free, almost limitless, clean stored energy could eventually replae polluting fossil and bio-energies for cooking, heating, lighting and for 2 to 18 Wheel transport vehicles.

Mas producing the converters and storage tanks should not be that difficult to do.

@Harvey

Hydrogen unlike electricity can be transported around the world.
That means that energy systems all over the world would be transformed, not just that in hot sunny places.

It would be just like petrol, but producible anywhere with good solar resources renewably.

It might be more convenient to make it into methanol or something, but if hydrogen can be made from solar cheaply and with reasonable efficiency it is basically game 0ver for any energy problems and the use of fossil fuel.

Hydrogen, transported around the world?  It's volumetrically unwieldy as gas, and energetically inefficient as liquid (and still unwieldy).

I see hydrogen being pushed by the people who insist that it's needed to manage the intermittency of the scalable renewables (wind + PV).  The coupling to the perovskite cells is pertinent here.  If you don't insist that July's sunlight must be stored against January's cold, a lot of the argument for hydrogen falls apart.  Yes, it would still be useful... but it would fit into far fewer niches.

If you wanted an ideal fuel, I'd go with propane.  Somewhere, some biologist is figuring out a way to drive the 4-carbon photosynthesis dark-phase carbon capture mechanism with NADP or directly with electricity.  Turning electricity plus cheaply-captured carbon into nice, dense liquid alkanes truly gets rid of the storage problem.

Ultimately, there's more than one way to decarbonize energy.  Green ideologues insist otherwise, but it looks like the actual ecology-minded are going to be able to work around them and prove their claims in the real world.  It's going to be acrimonious, among other things.

H2 with CO2 sequestered from power plants can make methanol, DME, gasoline, jet fuel and diesel. Use the carbon twice, reduce emissions.

The problem is that using the carbon twice is nowhere close to sufficient.  We'd need to use it at least 5 times, and probably more like 10.

God has spoken.

DaveMart, several authoritative studies we've swapped links to here have posited out thepat long distance H2 transport is not feasible.

"The energy required to pump H2 through pipelines is some 4.5 times higher than for natural gas per unit of delivered energy. As a consequence, long distances H2 transportation for energy use may not be economically competitive. Transportation costs to deliver gaseous H2 to refueling stations are in the range of $1-$2/GJ"

- IEA
http://www.iea.org/techno/essentials5.pdf

Although you have cited the possibility of including H2 in NG pipelines, the details really don't pan out (you would still need to deliver enormous quantities of NG, significant expenses I upgrading the pipelines, etc)

@EP:
There are umpteen pathways to make hydrogen into something more readily transportable, some of which I have already mentioned.

For the US those would not greatly matter though, as it could simply be piped from the southwest to other areas, as technology which has been in use for decades in the industrial sector, but has not been more generally used as it was not needed.

If hydrogen is cheap enough, it can be transported one way or another.

@evi:
They study I linked gave distributed costs as well as hydrogen production costs locally, in particular for hydrogen from biomass and electrolysis.

As noted, they already do transport hydrogen large distances through pipelines, and have done for decades.

How on earth you come to the conclusion that the study I linked for hydrogen admixed into NG pipelines 'don't really pan out' is a mystery, as the study authors as well as the relevant bodies in other countries such as Germany and Japan have clearly concluded that it does:

'f implemented with relatively low concentrations, less than 5%–15% hydrogen by volume, this strategy of storing and
delivering renewable energy to markets appears to be viable without significantly increasing risks associated with utilization of the gas blend in end-use devices (such as
household appliances), overall public safety, or the durability and integrity of the existing natural
gas pipeline network.'

Since this is the diametric opposite of what you are claiming the study says, I can only think that your prior position against the use of hydrogen has inhibited your ability to even parse adequately contrary positions.

That is something that we are all prone to, but that does not mean that if we are to perform any sensible evaluation at all we don't have to realise first our own bias, and to be determined to read the contrary position with as generous interpretation as possible.

http://www.nrel.gov/docs/fy13osti/51995.pdf
(page 6)

Piping pure hydrogen:
'Air Products had operated two hydrogen pipeline systems in Texas and Louisiana before joining them with a new 180-mile segment. The Gulf Coast Connection Pipeline (GCCP) is now able to provide hydrogen to customers along the 600-mile pipeline span from more than 20 hydrogen production facilities.

The company announced the pipeline project in 2010 and placed it onstream in August 2012 to begin supply of more than 1.2 billion cubic feet of hydrogen per day to Louisiana and Texas customers.'

http://www.greencarcongress.com/2012/10/ap-20121024.html

You certainly would not want to build out a pure hydrogen pipeline system to every house, which is the aasumption used to to try to show impractically large costs by opponents.

If you had a cheap source of hydrogen the US south west you could however build the large pipelines to take it to other US regions for local distribution mixed in the NG pipelines etc.

For anywhere in the lower 48 of the US the problem with solar is not inadequate amounts, but nor enough sun in winter.

Hydrogen use enables seasonal storage, and so overcomes that.

So if piping the hydrogen from the southwest where there is a lot of sun and land is cheap was not favoured for some reason, then hydrogen from solar could be produced locally, with the primary objection to solar overcome.

Solar enrgy is free and plentiful a few hours most every day.

Converting it to electricity is easy a relatively cheap (without storage) for 6 to 7 hours a day.

Some tranformation or e-energy storage is required to cover the other 16 to 18 hours a day.

H2 may become one of the most practical and cheapest way of storing solar energy for sunless hours.

H2 can always be reconverted into electric with large FCs when and if required.

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