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Researchers at MIT Develop New Water-Splitting Catalyst That Works Under Benign Conditions; a “Giant Leap”

Researchers at MIT—Prof. Daniel Nocera and Dr. Matthew Kanan—have developed a new water-splitting catalyst that is easily prepared from earth-abundant materials (cobalt and phosphorous) and operates in benign conditions: pH neutral water at room temperature and 1 atm pressure. A report on their discovery was published online 31 July 2008 in the journal Science.

The cobalt-phosphorous catalyst targets the generation of oxygen gas from water—the more complex of the two water-splitting half-cell reactions required (H2O/O2 and H2O/H2). Another catalyst generates the hydrogen. Although the new catalyst requires further work, it opens a very promising pathway for the development of systems that use artificial photosynthesis to store solar energy on a large scale in the form of O2 and H2 for subsequent use in a fuel cell.

Of the two reactions, the H2O/O2 reaction is considerably more complex. This reaction requires a four-electron oxidation of two water molecules coupled to the removal of four protons to form a relatively weak oxygen-oxygen bond. In addition to controlling this proton-coupled electron transfer (PCET), a catalyst must tolerate prolonged exposure to oxidizing conditions. Even at the thermodynamic limit, water oxidation requires an oxidizing power that causes most chemical functional groups to degrade. Accordingly, the generation of oxygen from water presents a significant challenge toward realizing artificial photosynthesis.

—Nocera and Kanan (2008)

Other water oxidation catalysts exist, including first-row spinel and perovskite metal oxides; and precious metals and precious metal oxides. The first requires concentrated basic solutions (pH>13) and moderate overpotentials (<400 mV); the second operate under acidic conditions (pH<1).

However, few catalysts operate under the conditions of photosynthesis, i.e. in neutral water under ambient conditions. Neutral water is oxidized at Pt electrodes and some precious metal oxides have been reported to operate electrocatalytically in neutral or weakly acidic solutions. The development of an earth-abundant, first-row catalyst that operates at pH 7 at low overpotential remains a fundamental chemical challenge. Here we report an oxygen-evolving catalyst that forms in situ upon anodic polarization of an inert electrode in neutral aqueous phosphate solutions containing Co2+. Oxygen generation occurs under benign conditions: pH = 7, 1 atm and room temperature.

—Nocera and Kanan (2008)

The new catalyst consists of cobalt metal, phosphate and an electrode, placed in water. When electricity—whether from a photovoltaic cell, a wind turbine or any other source—runs through the electrode, the cobalt and phosphate form a thin film on the electrode, and oxygen gas is produced. Combined with another catalyst, such as platinum, that can produce hydrogen gas from water, the system can duplicate the water splitting reaction that occurs during photosynthesis.

James Barber, a leading researcher in the study of photosynthesis who was not involved in this research, called the discovery by Nocera and Kanan a “giant leap” toward generating clean, carbon-free energy on a massive scale.

This is a major discovery with enormous implications for the future prosperity of humankind. The importance of their discovery cannot be overstated since it opens up the door for developing new technologies for energy production thus reducing our dependence for fossil fuels and addressing the global climate change problem

—James Barber, the Ernst Chain Professor of Biochemistry at Imperial College London

Currently available electrolyzers, which split water with electricity and are often used industrially, are not suited for artificial photosynthesis because they are very expensive and require a highly basic (non-benign) environment that has little to do with the conditions under which photosynthesis operates.

If artificial photosynthesis is to enable the storage of solar energy commensurate with global demand, water-splitting chemistry will need to be performed at a daunting scale. Storing the equivalent of the current energy demand would require splitting greater than 1015 mol/yr of water, which is roughly 100 times the scale of nitrogen fixation by the Haber Bosch process. [The Haber Bosch process  allows the mass synthesis of ammonia from nitrogen and hydrogen.]

The conditions under which water splitting is performed will determine how solar energy is deployed. The catalyst reported here has many elements of natural photosynthesis including its formation from earth abundant metal ions in aqueous solution, a plausible pathway for self-repair, a carrier for protons in neutral water and the generation of O2 at low overpotential, neutral pH, 1 atm and room temperature.

—Nocera and Kanan (2008)

More engineering work needs to be done to integrate the new scientific discovery into existing photovoltaic systems, but Nocera said he is confident that such systems will become a reality. Nocera is the  principal investigator for the Solar Revolution Project funded by the Chesonis Family Foundation and co-Director of the Eni-MIT Solar Frontiers Center.

This is just the beginning. The scientific community is really going to run with this.

—Daniel Nocera

Nocera hopes that within 10 years, homeowners will be able to power their homes in daylight through photovoltaic cells, while using excess solar energy to produce hydrogen and oxygen to power their own household fuel cell. Electricity-by-wire from a central source could be a thing of the past.

The project is part of the MIT Energy Initiative, a program designed to help transform the global energy system to meet the needs of the future and to help build a bridge to that future by improving today’s energy systems.

This project was funded by the National Science Foundation and by the Chesonis Family Foundation, which gave MIT $10 million this spring to launch the Solar Revolution Project, with a goal to make the large scale deployment of solar energy within 10 years.

Resources

  • M W Kanan and D G Nocera (2008) In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+. Science, doi: 10.1126/science.1162018

  • Robert F. Service (2008) New Catalyst Marks Major Step in the March Toward Hydrogen Fuel. Science 1 August 2008: Vol. 321. no. 5889, p. 62010.1126/science.321.5889.620

Comments

Healthy Breeze

1. Kudos to MIT for finding a cheaper, more environmentally-friendly way to make H2 gas.

2. But, what's the application?
For utility-scale solar thermal, it is more efficient and cheaper to store the energy as heat (molten salt retains the energy for up to a week with ~10% loss) prior to generating electricity.
For small-scale PV, now we have to have an H2 tank and fuel cell, too? That's taking the costs in the wrong direction.
For large-scale PV, what's the conversion cost to go from sunlight to H2 to electricity? I'd guess 50% in the real world.

As things thus stand, it will probably be over a decade before we have more PV power than we can consume during the sunniest part of the day, so costs may change considerably by then.

GdB

"Giant Leap" and no comments?

sac

I think there are few comments because people with our interests are not that exited about hydrogen anymore. I used to be... However, hydrogen is really just energy storage, so it will probably be a long time before it makes economic sense, if ever, for most large scale applications, and in my opinion, probably never for transportation. Niche applications perhaps.

ToppaTom

I was not aware that there were significant losses or difficulties in the existing electrolysis processes to make hydrogen from water.
And this does not tell me that there are. Or how much better this is.
And then they inform us ignoramuses that this will use electricity “from a photovoltaic cell, a wind turbine or any other source”. Well, we all know you can’t use wind electricity to make hydrogen; it has to be solar. And “a “flying leap” # toward generating clean, carbon-free energy on a massive scale.” It converts energy. Maybe we can accept that a wind turbine “generates” energy but when you convert 1 kWh of electricity into 0.7 kWh of H2 and O2, that’s for sure not “generating”.
I hope and assume they have discovered a much improved method of electrolyzing water and I congratulate them, but let’s see efficiency numbers not hyperbole.
(# for GdB)

DaveD

I'm usually the first guy on the blogs screaming bull ka-ka when anyone even mentions hydrogen around here. I just don't believe it can be cost effective to separate, store, distribute, etc, etc, etc...the whole hydrogen economy seems a fools dream to me.
But just this once....hmmmm...maybe there is something here?
Perhaps in a different scenario. No industrial size facility so no need for molten salt storage. Perhaps relatively simple tanks storing the H2 and O2 for later reuse to produce energy during the night?
Of course, this would mean that solar is suddenly so efficient that it not only powers your home during the day, but it also is capable of producing the H2 and O2 at the same time with all that extra energy. AND that there is a fuel cell sitting around that can use them to create electricity and it's so cheap that every household can have one.

hmmmm, nahhhh. Not any time remotely soon. But we can always dream.

gr

"Electricity-by-wire from a central source could be a thing of the past."

Presumably the cost of this process will somehow be competitive with other energy sources. But generating heat as with solar thermal, and then electricity seems a more efficient path at this stage. Interesting that as quickly as new energy sources/technologies are announced - new methods of making H2 appear. Could there be a "jockeying for position" here?

Sulleny

In light of the multitude of new announcements - it would appear that coal-fired plants with or without CCS - are destined for the scrap heap. In fact it looks more probable every day that energy generation is headed to de-centralized, non-transmitted power. This would be a paradigm changing step that would address the serious drawback of centralized power in favor of on-demand independent (localized) energy systems.

All of which nicely meets the newest mandate for a Declaration of Global Energy Independence. It's back to the future all over again.

Sulleny

Er, sorry folks, previous meant for DOE CCS announce.

jimbo

It will be interesting to see voltage and requirements necessary to make this work and the resulting efficiencies at producing oxygen, which seems the more difficult to produce. But if this works then our world changes dramatically. The oil producing nations can go to hell, to sink back to whatever neanderthal age they want to exist in. We will no longer be held hostage by oil/coal/nuclear, and plenty of jobs will be available, at least for a while. The process will be clean, and if implemented quickly will solve global warming issues, we can have our polar bears back. But there will be problems, perhaps mostly caused by those who will be displaced (oil, coal, nuclear). IMO this can't happen too quickly. Maybe we can also have our government back again.

Carlos

And a new fuel cell without platinum make this news more interesting
http://www.physorg.com/news136741749.html
Look what we need is hydrogen storage for a fuel cell car

jimbo

We always hear of some entity buying up a new technology that will save the world. Considering the impact this breakthrough can have (oil, coal, nuclear) I think it will be prudent to track progress in developing this potential new technology. I don't think we can trust our current government with this, considering its reliance on big oil, coal and nuclear with their lobbyests and big money. I mean, consider that the big energy breakthrough we hear about now is offshore drilling, which is so stupid at so many levels that if it weren't coming from our current administration I wouldn't believe it.

jimbo

We always hear of some entity buying up a new technology that will save the world. Considering the impact this breakthrough can have (oil, coal, nuclear) I think it will be prudent to track progress in developing this potential new technology. I don't think we can trust our current government with this, considering its reliance on big oil, coal and nuclear with their lobbyests and big money. I mean, consider that the big energy breakthrough we hear about now is offshore drilling, which is so stupid at so many levels that if it weren't coming from our current administration I wouldn't believe it.

Lee

Keep an open mind and remember that we need all the energy we can get. Trouble is that if every roadblock facing this new method was overcome tomorrow, all the other roadblocks like storage and transportation would still be firmly in place.

BB

I was under the impression that there was a theoretical limit to water electrolysis efficiency at room temperature (due to Gibbs free energy). I can't seem to find the figure right now, but something around 35% IIRC.

With the increase of temperature the efficiency rises (e.g. to 64% at 850°C), but again you need energy to heat the water up.

GreenPlease

The obvious application here is to have a dye sensitized solar cell with a titanium dioxide base on one side and then have the electrolytic catalysts on the other. Electricity produced by the TIO2 solar cell would go directly to power an electrolysis reaction which would help with one of the primary inefficiencies of TIO2 based solar cells (that is their low conductivity).

In the past such a proposition would have been insane because of the amount of platinum used. The device described above could harvest sunlight at maybe ~10% efficiency but with very cheap materials (except for cobalt, I thought that was expensive, no?)

I'm far from a hydrogen believer but if we can make it cheap enough we can get around some of the bigger problems.

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