GranBio begins producing cellulosic ethanol in Brazil; very low carbon intensity of 6.98 gCO2e/MJ for California LCFS
Toshiba delivers world’s first propulsion system integrating PMSM and SiC diode to Tokyo Metro

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

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.

LUO
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

Engineer-Poet

Dave... 5-15% by volume is about 2-5% by energy.  This scarcely qualifies as a minor contibution.

Davemart

@EP:

If 5-15% were some sort of ultimate limit, fair enough.
It is not, it is a good start which means that transitional issues can be coped with.

Here is a UK study, 2013, on converting the UK NG grid to hydrogen:
https://www.bartlett.ucl.ac.uk/energy/research/themes/energy-systems/hydrogen/dodds-demoullin-2013-gas-network-conversion

Some highlights:
The UK grid used to run on town gas, which was 50% hydrogen, so we should be able to cope with hydrogen with 21st century technology.

Although the energy density of hydrogen is lower than NG, the flow rate at the same pressure is higher, so the overall reduction in energy transported is only 20-30% less.

Most of the costs given here are for home appliances.

The present discussion centres on transport, so the costs are far smaller to just take hydrogen to hydrogen stations etc.

They put the cost of pipelines as a comparatively minor part of total costs even with the full conversion they are studying.

Here is the use of fibre reinforced pipes to transport hydrogen:
http://www.hydrogen.energy.gov/pdfs/review14/pd022_rawls_2014_o.pdf

Not every issue needs to be solved for all time before progress can be made.

Feeding hydrogen through natural gas pipes at a relatively low fraction reduces the transition costs considerably, but is no dead end to an impractical option.

Roger Pham

@ECI,

The EIA link that you provided estimated that electrolytic H2 can be produced for $30 /GJ(9.2 kg) TODAY or $3.2/kg with electricity cost of 3.5c/kWh, which is within range of raw RE output today, and $20/GJ or $2.17/kg in the near future. Lower-cost electrolytic equipments like described in this article can bring down the cost of electrolytic H2 even further, but not necessary!

Even though BEV's are twice as efficient as FCEV, BEV's are charged from grid electrity at 12c/kWh which costs 3x more than the raw electricity from RE at 4c/kWh when fed directly to the electrolyzers from solar PV's or wind turbines when bypassing the Grid. So, energy cost per mile of BEV's and FCEV's may be comparable.

Engineer-Poet
If 5-15% were some sort of ultimate limit, fair enough.

It's a limit at which you need to switch over to a dedicated transmission system.  That means lots and lost of costs, and you've only been carrying a tiny fraction of your total energy that way to that point.  This means also a sudden transition.

The UK grid used to run on town gas, which was 50% hydrogen
Except...
  1. Town gas was generated in the town.  It wasn't shipped cross-country.
  2. Town gas was manufactured more or less as needed.  It was not stored seasonally
Hydrogen is supposed to solve both the space-shifting and time-shifting problems of wind and solar.  It's no more suited to that role than town gas.
Here is a UK study, 2013, on converting the UK NG grid to hydrogen
From that report:
we identify concerns over the reduced capacity of the system and the much lower linepack storage compared to natural gas.

There's also the issue that leak rates through non-metallic distribution piping are high.  This may not be a safety hazard, but hydrogen presents some of the same problems for stratospheric chemistry that CFCs do.

Not every issue needs to be solved for all time before progress can be made.

The problem is that you've got so many issues, including low geographic power density, irregular supply not at all synchronized with demand, issues of storage, issues of shipment, and increased hazards at the point of use.  Or you could write a budget to solve the problem with AP1000s or ESBWRs, EVs for the transport side (with any liquid fuel derived from e.g. plasma-gasified garbage and surplus power), heat pumps for space heat (with dehumidifiers against the chronic English complaint of dampness), with all of the pieces available for contract bidding right now.

The real kicker?  The "revolutionary" renewable system could feed right into the same power grid, though you'd want to make it assume its own transmission and time-shifting costs.  You only need hydrogen if you're trying to get rid of nuclear.  That's what it's always been about.

Davemart

@EP:
The study I linked like any proper study highlights issues instead of being simply cheerleading.
However the overall conclusion is plain:
That it is perfectly practical to convert a natural gas network to carry as much hydrogen as is wanted, and at reasonable cost.

Town gas was local,sure, but this started off with 19th century materials and technology, not even 20th century.

The report I linked showed others, and I also linked to fibre pipes, and also to presently operational long distance hydrogen transport, so it is plain that it can be done.

I can only agree about nuclear, and I am hopeful that China will start mass producing nuclear plants at such low cost and in such quantity that Luddite objections in the West are overcome, so that the system is nuclear supplemented by solar.

There is little or nothing I can do t6 make that happen though, so I am looking at the possibilities of renewables with hydrogen, which at least has the virtue that it appears practical, and not a fancy way of burning vast quantities of fossil fuel lightly decorated by extraordinarily expensive renewables.

I don't fancy huge battery packs in any case, so my ideal system would perhaps be PHEVs progressing to PHEV FCEVs, with the FCEV element supplemented and perhaps gradually replaced by on the move inductive charging highways, powered by nuclear and solar where appropriate.

As soon as I am appointed dictator I propose to issue edicts to that effect, but meanwhile I muddle on, and try to evaluate what is actually being built! ;-)

HarveyD

Good observations DM. There are no doubts that REs are picking up from NPPs, CPP and NGPPs in many countries. With the current rate of change, REs may become the major energy (fixed) source in another 20 to 30 years.

Both intermittent Solar and Wind are fighting for first place. Eventually, unlimited free Solar, specially in sunny places, should win.

Storage technology used may vary from place to place but H2 may move in faster than expected.

Brotherkenny4

Only oil, coal and natural gas can be controlled by major corporations. All other alternatives will be plausible on small personal scale. There will always be those that do it themselves and as they get access to new tech the corporations will lose control of it. "Big hydrogen" will never happen.

The sun falls on every mans land and so does hydrogen containing water. You will need to build a shield against light and rain to control the world now.

The comments to this entry are closed.