New record energy efficiency for artificial photosynthesis

 

A new world-record 22 percent conversion efficiency for solar-powered hydrogen production has been claimed by researchers from Australia's Monash University (Credit: Shutterstock) As the world moves towards developing new avenues of renewable energy, the efficiencies of producing fuels such as hydrogen must increase to the point that they rival or exceed those of conventional energy sources to make them a viable alternative. Now researchers at Monash University in Melbourne claim to have created a solar-powered device that produces hydrogen at a world-record 22 percent efficiency, which is a significant step towards making cheap, efficient hydrogen production a reality. Efficiency records for solar-powered hydrogen production have continued to rise over the years, and much more rapidly as the technology and techniques improve. Even as late as December last year Gizmag reported a solar-driven hydrogen record efficiency at the time of just 12.3 percent, so this new record shows a very healthy 10 percent improvement on that and beats out the previous record of 18 percent. Splitting water using electricity to produce hydrogen and oxygen has been an established scientific technique for many decades. However, the rate at which hydrogen has been produced in this way has not been commercially viable due to the relatively low conversion rates compared to the input energy costs. Ideally, solar-powered water-splitting would be one of the best ways to produce hydrogen as its energy input cost is effectively zero. On the downside, however, the low efficiencies of past solar devices have kept this technology largely in its infancy. The Monash researchers believe that may all soon change as increased efficiencies in the process and in the devices themselves improve. "Electrochemical splitting of water could provide a cheap, clean and renewable source of hydrogen as the ultimately sustainable fuel." said Professor Leone Spiccia from the School of Chemistry at Monash who led the research. "This latest breakthrough is significant in that it takes us one step further towards this becoming a reality." According to the researchers, the breakthrough is significantly attributable to the leading-edge capabilities of the group in which they work and a growing expertise in tuning the processes and materials used in water splitting. To help achieve the required solar-input efficiencies, the team utilized the very best commercial-grade multi-junction (indium gallium phosphide, gallium arsenide, and germanium) solar cells available to ensure the maximum sunlight to electricity conversion. However, an even greater contribution to efficiency was on the material side, where the use of expanded foam nickel electrodes increased the available electrolysis surface area with such efficiency that the electrolyte in which they were immersed was simply local river water with the addition of a standard pH buffer (generally a salt solution containing sodium phosphate and sodium chloride). In this combination of high-efficiency cells and high-yield electrodes, the team claims the 22 percent record for conventional solar-cell to electrochemical production of hydrogen. What the eventual limit of such technologies is a largely moot point at this stage and largely reliant on the increasing efficiency of solar-cell light conversion factors. Advances in such things as perovskite solar-cells may assist in this regard and, compared to some other methods of sunlight-powered water-splitting yet to fully prove their mettle, may achieve the necessary breakthrough point to tip the balance in favor of cheap, abundant hydrogen fuel. "Hydrogen can be used to generate electricity directly in fuel cells," said Professor Doug MacFarlane, ARC Laureate Fellow and leader of the Energy Program of the ARC Centre of Excellence for Electromaterials Science at Monash. "Cars driven by fuel cell electric engines are becoming available from a number of car manufacturers. Hydrogen could even be used as an inexpensive energy storage technology at the household level to store energy from roof-top solar cells." The results of the research were recently published in the journal Energy and Environmental Science. Source: Monash University

Hydrogen production in extreme bacterium

 

A researcher at Missouri University of Science and Technology has discovered a bacterium that can produce hydrogen, an element that one day could lessen the world's dependence on oil. Dr. Melanie Mormile, professor of biological sciences at Missouri S&T, and her team discovered the bacterium Halanaerobium hydrogeninformans in Soap Lake, Washington. It can "produce hydrogen under saline and alkaline conditions in amounts that rival genetically modified organisms," Mormile says. "Usually, I tend to study the overall microbial ecology of extreme environments, but this particular bacterium has caught my attention," Mormile says. "I intend to study this isolate in greater detail." Mormile, an expert in the microbial ecology of extreme environments, wasn't searching for a bacterium that could produce hydrogen. Instead, she first became interested in bacteria that could help clean up the environment, especially looking at the extremophiles found in Soap Lake. An extremophile is a microorganism that lives in conditions of extreme temperature, acidity, alkalinity or chemical concentration. Living in such a hostile environment, Halanaerobium hydrogeninformans has metabolic capabilities under conditions that occur at some contaminated waste sites. With Halanaerobium hydrogeninformans, she expected to find an iron-reducing bacterium and describe a new species. What she found was a new species of bacterium that can produce hydrogen and 1, 3-propanediol under high pH and salinity conditions that might turn out to be valuable industrially. An organic compound, 1, 3-propenediol can be formulated into industrial products including composites, adhesives, laminates and coatings. It's also a solvent and can be used as antifreeze. The infrastructure isn't in place now for hydrogen to replace gasoline as a fuel for planes, trains and automobiles. But if hydrogen becomes an alternative to gasoline, Halanaerobium hydrogeniformans, mass-produced on an industrial scale, might be one solution -- although it won't be a solution anytime soon. "It would be great if we got liters and liters of production of hydrogen," Mormile says. "However, we have not been able to scale up yet." In her first single-author article, Mormile's findings were featured in the Nov. 19 edition of Frontiers in Microbiology. Mormile holds two patents for her work on the Soap Lake bacterium's biohydrogen formation under very alkaline and saline conditions. Also named on the patents are Dr. Judy Wall, Curators' Professor of Biochemistry and Joint Curators' Professor of Molecular Microbiology & Immunology at the University of Missouri-Columbia, and her former lab members, Matthew Begemann and Dwayne Elias. A pending patent application, submitted along with Elias; Dr. Oliver Sitton, professor of chemical and biochemical engineering at Missouri S&T; and Daniel Roush, then a master's student for Mormile, is for the conversion of glycerol to 1, 3-propanediol, also under hostile alkaline and saline conditions. This patented and patent-pending technology is available for licensing through the Missouri S&T Center for Technology Transfer and Economic Development. Story Source: The above story is based on materials provided by Missouri University of Science and Technology. The original article was written by Joe McCune. Note: Materials may be edited for content and length. Journal Reference: Melanie R. Mormile. Going from microbial ecology to genome data and back: studies on a haloalkaliphilic bacterium isolated from Soap Lake, Washington State. Frontiers in Microbiology, 2014; 5 DOI: 10.3389/fmicb.2014.00628

Why Coconuts Could Be The Hydrogen Storage Material Of The Future

 

Coconut flesh contains secret ingredients that dramatically enhance its ability to store hydrogen, say material scientists.

Hydrogen is a potential renewable fuel because it can easily be generated from water using electrolysis. It also burns cleanly to produce water vapour. The hope is that it could also be distributed using the same global network of liquid fuel transport that moves petrol around the planet.

But there numerous problems with this dream of a hydrogen-based economy. One of them is that hydrogen is difficult to store efficiently. Hydrogen gas has a poor energy density by volume compared to petrol. In fact, there is at least 60 percent more hydrogen in a litre of gasoline then there is in a litre of pure liquid hydrogen. In other words, hydrogen will always require bigger tanks.

So finding ways to store more of it is a huge challenge. One option is to store it as a liquid but hydrogen boils temperatures above -250 degrees centigrade and so requires bulky insulation to keep it in this state.

Another idea is to compress it. But this raises issues of safety should a hydrogen-fuelled car be involved in a collision.

That is why much of the material science research in this area has focused on chemical storage: finding materials that adsorb hydrogen efficiently and then release it again when it is required.

Now Viney Dixit and buddies at the Hydrogen Energy Center of Banaras Hindu University in India say they have discovered that carbonised coconut flesh is particularly good at this task. Today, they show that it outperforms a number of other hydrogen storage materials, particularly in its ability to work over many charging cycles.

To help evaluate hydrogen storage materials, the US Department of Energy has set a number of targets that these materials must meet to be considered viable technologies for future transport systems. For example, the current criteria is that a hydrogen storage system must store at least 5.5 per cent of hydrogen by mass (5.5 wt %).

This is the mass of the entire storage system and not just the mass of the storage material. So clearly the mass fraction of the storage material must be considerably higher.

Material scientists originally focused their efforts on metal hydrides, some of which can store hydrogen at higher fractions than the DoE criteria. However, these materials have a number of disadvantages. First, they need to be heated to release the hydrogen and this takes energy. Worse, the materials tend to physically break down as the number of charging cycles increase beyond 100 or so.

So in recent years, researchers have turned their attention to carbon. The bond between hydrogen and carbon is known to be quick and reversible. What’s more, it is relatively straightforward to create strong, porous carbon with a high surface area.

One way of doing this is to carbonise biological material, such as fruit or coconut shell. This means heating the material to few hundred degrees centigrade in a nitrogen atmosphere which ensures that the carbon retains its porous biological structure.

Instead of coconut shell, Dixit and co carbonised coconut flesh. They say this has the advantage of containing a wide variety of additional elements, such as potassium, sodium, calcium and magnesium, which are evenly distributed throughout the carbon matrix. And they say this turns out to be significant in their experiments.

These guys have measured the amount of hydrogen that carbonised coconut flesh can hold and say it compares well with more conventional materials. “The synthesized material adsorbs 2.30 wt % at room temperature and 8.00 wt %  at liquid nitrogen temperature under 70 atm pressure,” say Dixit and co.

What’s more, the material releases hydrogen quickly and efficiently and does not appear to degrade over many charging cycles.

Whether that is good enough to meet the DoE’s 5.5 wt % criterion for an entire storage system has yet to be seen.

The team spent some time studying the microstructure of the carbonised coconut flesh to work out why it perform so well. And they have pinpointed two mechanisms.

The first is that the carbonised coconut flesh contains a significant amount of potassium chloride, which polarises the carbon matrix in which it is embedded.  “This will enhance the hydrogen adsorption capacity,” they say.

The second is that the carbon matrix also contains significant amounts of magnesium, which is known to enhance the dissociation of hydrogen molecules, making them easier to adsorb.

That is an interesting result that suggests some promising avenues for future research. The presence of molecules that catalyse the adsorption of hydrogen looks to be an important mechanism. It may even be possible to adjust these proportions by growing coconuts in different environments. Another possibility might be to artificially synthesise carbon that matches some of the characteristics of carbonised coconut flesh.

Either way, material scientists might profitably hang their hammocks between some coconut trees in future.

Ref: arxiv.org/abs/1409.7219  : Hydrogen Storage In Carbon Derived From Solid Endosperm Of Coconut

Efficiently harvesting hydrogen fuel from Sun using Earth-abundant materials

 

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When an electrical current is applied, water splits into hydrogen and oxygen.

The race is on to optimize solar energy's performance. More efficient silicon photovoltaic panels, dye-sensitized solar cells, concentrated cells and thermodynamic solar plants all pursue the same goal: to produce a maximum amount of electrons from sunlight. Those electrons can then be converted into electricity to turn on lights and power your refrigerator.

At the Laboratory of Photonics and Interfaces at EPFL, led by Michael Grätzel, where scientists invented dye solar cells that mimic photosynthesis in plants, they have also developed methods for generating fuels such as hydrogen through solar water splitting.

To do this, they either use photoelectrochemical cells that directly split water into hydrogen and oxygen when exposed to sunlight, or they combine electricity-generating cells with an electrolyzer that separates the water molecules.

By using the latter technique, Grätzel's post-doctoral student Jingshan Luo and his colleagues were able to obtain a performance so spectacular that their achievement is being published today in the journal Science. Their device converts into hydrogen 12.3 percent of the energy diffused by the sun on perovskite absorbers -- a compound that can be obtained in the laboratory from common materials, such as those used in conventional car batteries, eliminating the need for rare-earth metals in the production of usable hydrogen fuel.

Bottled sun

This high efficiency provides stiff competition for other techniques used to convert solar energy. But this method has several advantages over others:

"Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap," explained Jingshan Luo. "However, our electrodes work just as well as the expensive platinum-based models customarily used."

On the other hand, the conversion of solar energy into hydrogen makes its storage possible, which addresses one of the biggest disadvantages faced by renewable electricity -- the requirement to use it at the time it is produced.

"Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it," said Michael Grätzel. Such a gas can indeed be burned -- in a boiler or engine -- releasing only water vapor. It can also pass into a fuel cell to generate electricity on demand. And the 12.3% conversion efficiency achieved at EPFL "will soon get even higher," promised Grätzel.

More powerful cells

These high efficiency values are based on a characteristic of perovskite cells: their ability to generate an open circuit voltage greater than 1 V (silicon cells stop at 0.7 V, for comparison).

"A voltage of 1.7 V or more is required for water electrolysis to occur and to obtain exploitable gases," explained Jingshan Luo. To get these numbers, three or more silicon cells are needed, whereas just two perovskite cells are enough. As a result, there is more efficiency with respect to the surface of the light absorbers required. "This is the first time we have been able to get hydrogen through electrolysis with only two cells!" Luo adds.

The profusion of tiny bubbles escaping from the electrodes as soon as the solar cells are exposed to light say it better than words ever could: the combination of sun and water paves a promising and effervescent way for developing the energy of the future.

Video: http://www.youtube.com/watch?v=hkGAqk-TXw8&feature=youtu.be

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Story Source:

The above story is based on materials provided by Ecole Polytechnique Fédérale de Lausanne. Note: Materials may be edited for content and length.

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Journal Reference:

1. 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. Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts. Science, 26 September 2014: 1593-1596 DOI: 10.1126/science.1258307

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