Green Car Congress  
Go to GCC Discussions forum About GCC Contact  RSS Subscribe Twitter headlines

« Opel with OnStar connectivity beginning in 2015 | Main | Taxi Electric in Amsterdam first to adopt the Nissan e-NV200 »

Print this post

JCAP hybrid photocathode material shows promising performance in conversion of solar energy to hydrogen

9 March 2014

A new study by Berkeley Lab researchers at the Joint Center for Artificial Photosynthesis (JCAP) shows that nearly 90% of the electrons generated by a new hybrid photocathode material designed to store solar energy in hydrogen are being stored in the target hydrogen molecules (Faradaic efficiency).

Gary Moore, a chemist and principal investigator with Berkeley Lab’s Physical Biosciences Division, led an efficiency analysis study of the material he and his research group have developed for catalyzing the production of hydrogen fuel from sunlight. (Earlier post.) This material, a p-type (100) gallium phosphide (GaP) semiconductor functionalized with molecular hydrogen-producing cobaloxime catalysts via polymer grafting, has the potential to address one of the major challenges in the use of artificial photosynthesis to make renewable solar fuels.

The catalysts belong to the cobaloxime class of compounds that have shown recent promise in electrocatalysis and solar-to-fuels applications. Attachment of the complex to a semiconductor surface allows direct photoelectrochemical (PEC) measurements of performance.

Under simulated air mass 1.5 illumination, the catalyst-modified photocathode yields a 0.92 mA cm-2 current density when operating at the equilibrium potential for the hydrogen production half reaction. The open circuit photovoltage (VOC) is 0.72 V vs. a reversible hydrogen electrode (RHE) and the fill factor (FF) is 0.33 (a 258% increase compared to polymer-modified electrodes, without cobaloxime treatment).

The external quantum efficiency (EQE), measured under a reverse bias of +0.17 vs. RHE, shows a maximum of 67% under 310 nm illumination. Product analysis of the head-space gas yields a lower limit on the Faradaic efficiency of 88%. In addition, the near linear photoresponse of the current density upon increasing illumination indicates that photocarrier transport to the interface can limit performance.

—Krawicz et al.

A paper describing this research is published in the RSC journal Physical Chemistry Chemical Physics.

Ultimately the renewable energy problem is really a storage problem. Given the intermittent availability of sunlight, we need a way of using the sun all night long. Storing solar energy in the chemical bonds of a fuel also provides the large power densities that are essential to modern transport systems. We’ve shown that our approach of coupling the absorption of visible light with the production of hydrogen in a single material puts photoexcited electrons where we need them to be, stored in chemical bonds.

—Gary Moore

Bionic leaves that produce energy-dense fuels from nothing more than sunlight, water and atmosphere-warming carbon dioxide, with no byproducts other than oxygen, represent an ideal sustainable energy alternative to fossil fuels. However, realizing this artificial photosynthesis ideal will require a number of technological breakthroughs including high performance photocathodes that can catalyze fuel production from sunlight alone.

Last year, Moore and his research group at JCAP took an important step towards the photocathode goal with their gallium phosphide/cobaloxime hybrid. Gallium phosphide is an absorber of visible light, which enables it to produce significantly higher photocurrents than semiconductors that only absorb ultraviolet light. The cobaloxime catalyst is also Earth-abundant, meaning it is a relatively inexpensive replacement for the highly expensive precious metal catalysts, such as platinum, currently used in many solar-fuel generator prototypes.

The novelty of our approach is the use of molecular catalytic components interfaced with visible-light absorbing semiconductors. This creates opportunities to use discrete three-dimensional environments for directly photoactivating the multi-electron and multi-proton chemistry associated with the production of hydrogen and other fuels.

—Gary Moore

The efficiency analysis performed by Moore and his colleagues also confirmed that the light-absorber component of their photocathode is a major bottleneck to obtaining higher current densities. Their results showed that of the total number of solar photons striking the hybrid-semiconductor surface, measured over the entire wavelength range of the solar spectrum (from 200 to 4,000 nanometers) only 1.5% gave rise to a photocurrent.

This tells us that the use of light absorbers with improved spectral coverage of the sun is a good start to achieving further performance gains, but it is likely we will also have to develop faster and more efficient catalysts as well as new attachment chemistries. Our modular assembly method provides a viable strategy to testing promising combinations of new materials.

Efficiency is not the only consideration that should go into evaluating materials for applications in solar-fuel generator technologies. Along with the durability and feasible scalability of components, the selectivity of photoactivating a targeted reaction is also critical. This is where molecular approaches offer significant opportunities, especially in catalyzing complex chemical transformations such as the reduction of carbon dioxide.

—Gary Moore

JCAP, which has a northern branch in Berkeley and a southern branch on the campus of the California Institute of Technology (Caltech), was established in 2010 by the US Department of Energy (DOE) as an Energy Innovation Hub. Operated as a partnership between Caltech and Berkeley Lab, JCAP is the largest research program in the United States dedicated to developing an artificial solar-fuel technology. It is funded through the DOE Office of Science.

Resources

  • Alexandra Krawicz, Diana Cedeno and Gary F. Moore (2014) “Energetics and Efficiency Analysis of a Cobaloxime-Modified Semiconductor at Simulated Air Mass 1.5 Illumination,” Phys. Chem. Chem. Phys. doi: 10.1039/C4CP00495G

March 9, 2014 in Hydrogen Production, Solar, Solar fuels | Permalink | Comments (56) | TrackBack (0)

TrackBack

TrackBack URL for this entry:
http://www.typepad.com/services/trackback/6a00d8341c4fbe53ef01a5117f8591970c

Listed below are links to weblogs that reference JCAP hybrid photocathode material shows promising performance in conversion of solar energy to hydrogen:

Comments

"Ultimately the renewable energy problem is really a storage problem."
No, it's not a problem at all. The H2 can be used in a further catalytic process to synthesize methane which is identical to NG. Methane gas can be stored without losses for long time periods. With the right FCs, methane gas can be converted to electric power as needed.
http://phys.org/news/2013-07-scalable-carbon-nanotube-based-catalyst-outperforming.html
http://phys.org/news/2013-06-metal-free-catalyst-outperforms-platinum-fuel.html

The problem with RE storage as H2 isn't using it, it's producing it at a price that won't make you faint dead away.

Dramatic falls in cost are making renewable energy competitive with fossil fuels across the world, and the least-cost option in a growing number of markets. For example, solar energy has already become cheaper than diesel generation, with clear benefits for communities in areas far away from the electricity grid.
http://cleantechnica.com/2013/09/11/analysis-50-reduction-in-cost-of-renewable-energy-since-2008/

@al
In some sunny places, solar is competitive with fossil while the sun shines: once it goes down, you have to fall back on some dispatchable fuel, such as fossil or hydro.

Thus, you can reduce your diesel usage by say 30-50% (depending on how much electricity you need for the other 16-18 hours). But you won't get it to zero any time soon without massive storage and massive costs.

Better to have a balance system with some renewables, some storage and some dispatchables.

Good point, however: Key factor seems to be that we expect “grid parity”, the point where solar+storage costs undercut the cost of utility power, – to come within the 30 year lifetime of conventional power plants being built today.

That means potential huge stranded assets for utilities and their shareholders, unless plans are made for a smooth transition to new technology. Based on the record of technological innovation in recent decades, I’d bet that grid-parity will come sooner, rather than later, than projections.

http://climatecrocks.com/2014/03/10/energy-storage-solar-a-game-changer/

The future will be a lot of hydrogen fuelcell cars and suvs feeded by solar/electricity hydrogen making machines that will be situated at the point of sale. No more pollution, transport, refining. Also they can put these solar hydrogen panels of the roof of hydrogen cars. Manufacturers of cars that do not do this like tesla and Nissan will go bankrupt.

Alternative clean energy sources and vehicles could become competitive when all direct and indirect fossil and bio-fuels cost are duly included.

Progressive carbon-pollution emission fees could level the playing field by 2025 or within 10-15 years or so. Fees application could be very easy with a progressive (monthly) Fed liquid fuel tax increase. A similar progressive e-energy tax on electricity produced by CPPs and (NGPPs to a lesser extend) and other polluting plants would make those non-competitive over a few years.

By 2035 or so, many (or most) CPPs, NGPPs and ICEVs would be replaced by pollution free units.

CHP with fuel SOFCs in the home could reduce energy use, provide electricity at night, and charge your car. Assuming fuel cell technology continues to advance rapidly.

@gor - Keepin' the dream alive!

The author of Climate Crocks is a documentarian.  The commenters seem to be non-technical people.  None of them will do arithmetic to see if a claim makes sense, or if it will work out or not.  They relentlessly down-vote anyone who does, and doesn't get an answer they like.

California is demanding that utilities install storage to manage the un-schedulable output of "renewables".  Meanwhile, the "renewables" enjoy subsidized costs, dispatch priority and outright mandates for their use.  Anyone can make a profit under such circumstances, and anyone trying to compete with such legislated winners is bound to lose.  There is no "competition", it's rent-seeking at its worst.

If the "renewables" had to install batteries to buffer their variability themselves and supply power at contracted levels and defined ramp rates, they'd be a lot less profitable.  If they had to buffer energy for days to cover lulls, they'd go out of business.

A system using base-load plants plus storage only needs storage for a fraction of a day's power and can cycle the storage daily, making the cost per kWh rather low.  A system using "renewables" not only requires far more storage, but it has to be able to charge it faster when the power is available because it is "use it or lose it".  The cost per kWh is correpondingly much higher.  The breakeven price of storage to reach parity with peakers is much higher for base load than renewables, because the smaller capacity and more frequent cycling spreads the cost of storage over a lot more kWh.

Existing CPPs, NGPPs, and Nuke e-energy sources are currently cheaper than cleaner e-energy sources with storage, because pollution, used fuel storage or re-cycling and direct + indirect clean-up and health care cost are not included.

Japan will be paying for those indirect cost for the next 4 to 6 decades.

@ HD
Harvey, I'm proud of you; I couldn't have stated it better.

The author of Climate Crocks may be just a documentarian but his conclusions are suppored by the work of such as the global financial advisor and asset manager firm Lazard Freres & Co.
http://cleantechnica.com/2013/09/11/analysis-50-reduction-in-cost-of-renewable-energy-since-2008/

"In fact, Lazard finds certain forms of renewable energy generation are now cost-competitive with many fossil fuel generation sources at an unsubsidized LCOE, even before factoring in externalities like pollution or transmission costs."

Sooner or later, somebody will establish ALL the hidden (environmental, pollution, radiation, clean-up, storage, lost productivity, health care etc) cost for every energy source type.

It is not easy to do and would certainly require governmental participation and/or active supervision to get unbiased results.

It could become an interesting research project for our universities. Every e-energy sources TOTAL COST could be evaluated by 3 different universities to arrive at an more accurate average TOTAL COST.

ai_vin, the cost of energy is one thing; the cost of dispatchable power matching the demand curve is another thing entirely.

And that's where storage comes in to it, the cost of which is also on its way down.

Cost of delivered e-energy is very relative because the real TOTAL Cost is unknown.

There's also this; http://www.greentechmedia.com/articles/read/this-is-what-the-utility-death-spiral-looks-l

On the cost of delivered solar e-energy; http://www.mystatesman.com/news/news/austin-energy-close-to-signing-cheapest-solar-powe/nd8BF/

Austin Energy is poised to sign what could be the world’s cheapest solar-power deal.

The city-owned electric utility has agreed to terms with SunEdison to buy electricity from two solar farms in West Texas, one a 350,000-panel, 100-megawatt facility, the other a nearby 150,000-panel, 50-megawatt neighbor. The price is just below 5 cents per kilowatt-hour. That is far cheaper than solar energy had generally been going for — and less than a third of the price Austin Energy agreed to pay in 2009 for electricity from a much smaller solar array just east of the city.

“It’s the cheapest I’ve seen,” said Raj Prabhu, the CEO of Mercom Capital Group, an Austin-based energy consulting group that monitors the industry nationally. He said he isn’t familiar with the details but added, “This seems to be new territory.”

At that very low price ($0.05/kWh), it probably does not include storage cost? If it does, CPPs, NGPPs, NPPs will be out of business soon, specially for sunny places.

At that price, there is NO storage.  What you get for 5¢/kWh isn't dispatchable power, it's energy-whenever-nature-gives-it-to-you.

Turning it into dispatchable power is very expensive.  It is likely much cheaper to turn it into a direct offset to electric consumption elsewhere using ice storage or conversion to DHW.  If you simply feed it to the grid with no other measures, you need other powerplants to ramp up and down to track the variations in the net load (the so-called "duck belly" problem) and you both suffer efficiency losses in the other generators and wear and tear from the rapid cycling.

The evening demand peak from cooking and other needs is not going to be supplied by PV when the sun is near the horizon or already set.  Handling that without burning fossil carbon takes batteries, and batteries aren't cheap.  Worse, when you include storage with your PV system your EROI drops to around 2.

Truly greening the electrical grid cannot be done with PV without radical improvements in several technologies.

With wide area East-West grids, the Eastern regions evening peak can be supplied by West Coast solar farms.
The West Coast peak could be covered by reduced night time consumption in the East Coast regions etc.

Of course a certain amount of storage will always be required. It could be done with local H2 storage + large FCs.

In our region we have plenty of variable Hydro to do it with. We could easily supply clean Hydro power to the East Coast region as back up.

In our region hydro also dominates but we do have to use thermal power plants to deal with seasonal variation in precipitation. Even just using solar to offload some of the demand on hydro would allow us to store more water between the seasons. The thermal power plants could/should become redundant.

So the "local, democratic" power envisioned by the Greens involves "wide area East-West grids".

One cannot build what is a contradiction in terms.

That sounds like a strawman attack.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Green Car Congress © 2013 BioAge Group, LLC. All Rights Reserved. | Home | BioAge Group