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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
In a new study from the U.S. Department of Energy's Argonne National Laboratory and the University of Illinois at Chicago, researchers have found a way to convert carbon dioxide into a usable energy source by using sunlight. Credit: © Romolo Tavani / Fotolia
In a new study from the U.S. Department of Energy's Argonne National Laboratory and the University of Illinois at Chicago, researchers have found a way to convert carbon dioxide into a usable energy source by using sunlight. Credit: © Romolo Tavani / Fotolia
As scientists and policymakers around the world try to combat the increasing rate of climate change, they have focused on the chief culprit: carbon dioxide.

Produced by the burning of fossil fuels in power plants and car engines, carbon dioxide continues to accumulate in the atmosphere, warming the planet. But trees and other plants do slowly capture carbon dioxide from the atmosphere, converting it to sugars that store energy.

In a new study from the U.S. Department of Energy's Argonne National Laboratory and the University of Illinois at Chicago, researchers have found a similar way to convert carbon dioxide into a usable energy source using sunlight.

One of the chief challenges of sequestering carbon dioxide is that it is relatively chemically unreactive. "On its own, it is quite difficult to convert carbon dioxide into something else," said Argonne chemist Larry Curtiss, an author of the study.

To make carbon dioxide into something that could be a usable fuel, Curtiss and his colleagues needed to find a catalyst -- a particular compound that could make carbon dioxide react more readily. When converting carbon dioxide from the atmosphere into a sugar, plants use an organic catalyst called an enzyme; the researchers used a metal compound called tungsten diselenide, which they fashioned into nanosized flakes to maximize the surface area and to expose its reactive edges.

While plants use their catalysts to make sugar, the Argonne researchers used theirs to convert carbon dioxide to carbon monoxide. Although carbon monoxide is also a greenhouse gas, it is much more reactive than carbon dioxide and scientists already have ways of converting carbon monoxide into usable fuel, such as methanol. "Making fuel from carbon monoxide means travelling 'downhill' energetically, while trying to create it directly from carbon dioxide means needing to go 'uphill,'" said Argonne physicist Peter Zapol, another author of the study.

Although the reaction to transform carbon dioxide into carbon monoxide is different from anything found in nature, it requires the same basic inputs as photosynthesis. "In photosynthesis, trees need energy from light, water and carbon dioxide in order to make their fuel; in our experiment, the ingredients are the same, but the product is different," said Curtiss.

The setup for the reaction is sufficiently similar to nature that the research team was able to construct an "artificial leaf" that could complete the entire three-step reaction pathway. In the first step, incoming photons -- packets of light -- are converted to pairs of negatively-charged electrons and corresponding positively-charged "holes" that then separate from each other. In the second step, the holes react with water molecules, creating protons and oxygen molecules. Finally, the protons, electrons and carbon dioxide all react together to create carbon monoxide and water.

"We burn so many different kinds of hydrocarbons -- like coal, oil or gasoline -- that finding an economical way to make chemical fuels more reusable with the help of sunlight might have a big impact," Zapol said.

Towards this goal, the study also showed that the reaction occurs with minimal lost energy -- the reaction is very efficient. "The less efficient a reaction is, the higher the energy cost to recycle carbon dioxide, so having an efficient reaction is crucial," Zapol said.

According to Curtiss, the tungsten diselenide catalyst is also quite durable, lasting for more than 100 hours -- a high bar for catalysts to meet.

The study, "Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid," is published in Science. Much of the experimental work was performed at the University of Illinois at Chicago, while the computational work was performed at Argonne.

Source:
The above post is reprinted from materials provided by Argonne National Laboratory.

Reference:
M. Asadi, K. Kim, C. Liu, A. V. Addepalli, P. Abbasi, P. Yasaei, P. Phillips, A. Behranginia, J. M. Cerrato, R. Haasch, P. Zapol, B. Kumar, R. F. Klie, J. Abiade, L. A. Curtiss, A. Salehi-Khojin. Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid. Science, 2016; 353 (6298): 467 DOI: 10.1126/science.aaf4767
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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas. Credit: University of Illinois at Chicago/Jenny Fontaine
Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas. Credit: University of Illinois at Chicago/Jenny Fontaine
Researchers at the University of Illinois at Chicago have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.

The finding is reported in the July 29 issue of Science and was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.

Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel, solving two crucial problems at once. A solar farm of such "artificial leaves" could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.

"The new solar cell is not photovoltaic -- it's photosynthetic," says Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.

"Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight," he said.

While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas, a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.

The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.

Chemical reactions that convert CO2 into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO2 reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.

"What we needed was a new family of chemicals with extraordinary properties," he said.

Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides -- or TMDCs -- as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell.

The best of several catalysts they studied turned out to be nanoflake tungsten diselenide.

"The new catalyst is more active; more able to break carbon dioxide's chemical bonds," said UIC postdoctoral researcher Mohammad Asadi, first author on the Science paper.

In fact, he said, the new catalyst is 1,000 times faster than noble-metal catalysts -- and about 20 times cheaper.

Other researchers have used TMDC catalysts to produce hydrogen by other means, but not by reduction of CO2. The catalyst couldn't survive the reaction.

"The active sites of the catalyst get poisoned and oxidized," Salehi-Khojin said. The breakthrough, he said, was to use an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.

"The combination of water and the ionic liquid makes a co-catalyst that preserves the catalyst's active sites under the harsh reduction reaction conditions," Salehi-Khojin said.

The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side.

When light of 100 watts per square meter -- about the average intensity reaching Earth's surface -- energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.

"The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction," said Asadi.

The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said. In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.

"This work has benefitted from the significant history of NSF support for basic research that feeds directly into valuable technologies and engineering achievements," said NSF program director Robert McCabe.

"The results nicely meld experimental and computational studies to obtain new insight into the unique electronic properties of transition metal dichalcogenides," McCabe said. "The research team has combined this mechanistic insight with some clever electrochemical engineering to make significant progress in one of the grand-challenge areas of catalysis as related to energy conversion and the environment."

Source:
The above post is reprinted from materials provided by University of Illinois at Chicago.

Reference:
Mohammad Asadi et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid. Science, July 2016 DOI: 10.1126/science.aaf4767
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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
Solar Power. Credit: Liam / flickr
Solar Power. Credit: Liam / flickr
As climate change garners more attention around the world, scientists at the University of Virginia and Cornell University have made critical advances in understanding the physical properties of an emerging class of solar cells that have the potential to dramatically lower the cost of solar energy.

Solar cells remain a focal point of scientific investigation because the sun offers the most abundant source of energy on earth. The concern, however, with conventional solar cells made from silicon is their cost. Even with recent improvements, they still require a significant amount of electricity and industrial processing to be manufactured.

In 2009, energy researchers turned their attention to a class of materials called "metal halide perovskites," or MHPs. They are sprayed on like paint onto solid objects, says Joshua Choi, an assistant professor of chemical engineering at the University of Virginia. As the solution dries, the MHPs crystallize into a thin film that can be used to capture energy in a solar cell.

Within just a few years, MHP solar cells have been crafted whose performance rivals conventional silicon solar cells. This is the fastest recorded improvement in history for any photovoltaic material and it has been verified by the National Renewable Energy Laboratory in Golden, Colorado.

The challenge is that these existing MHP solar cells are no larger than a human fingernail.

"To be really technologically relevant," Choi said, "we need to be able to scale up this process while maintaining or even improving the efficiency of the solar cell. To do that, we need to understand how this material crystallizes and grows from solution into a thin film."

Collaborating with scientists from Cornell University's High Energy Synchrotron Source, which receives funding from the National Science Foundation, Choi and his team monitored in real time the growth of MHP crystals at the atomic level by exposing them to high intensity X-rays.

The scientists will present their findings at the 66th meeting of the American Crystallographic Association, held July 22-26 in Denver, Colorado.

By adding different chemicals to the solution, they were able to control how fast the MHP crystals formed and what direction they grew on a surface. The specific orientation of the MHP crystals on a surface affected how well a solar cell performed, Choi said.

Moreover, this research provides this nascent field with the kinds of insights about MHP crystal formation that scientists will need as they determine how to manufacture the larger MHP solar cells that could reduce the price of solar energy.

But there's more to MHP solar cells than just their potential to cut costs.

"MHP solar cells can be used in flexible, lightweight materials," Choi said. The ultimate goal would be to make manufacturing MHP solar cells as easy as printing newspapers, generating rolls of thin solar cell material that could be easily applied to houses, cars, or anywhere else they were needed.

One significant drawback with many current MHP solar cells is that they contain lead. Researchers are working on identifying viable alternative compositions that are not toxic.

Choi and his research are funded by NASA, which is examining the potential for MHPs to be used in high temperature solar cells that could be installed in solar probes deployed in space. Elsewhere, MHPs have already been used in lasers, photo detectors, transistors and light emitting diodes (LEDs).

Still, it is the solar cell that arguably offers MHPs the best chance to address pressing global problems.

"To mitigate the impact of climate change and also to ensure the energy security of the United States and the world, it is very important to come up with renewable energy sources rather than just be relying on fossil fuel-based energy," Choi said.
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Source:
The above post is reprinted from materials provided by American Institute of Physics (AIP).
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Garden grass could become a source of cheap and clean renewable energy, scientists claim. Credit: © Kurhan / Fotolia
Garden grass could become a source of cheap and clean renewable energy, scientists claim. Credit: © Kurhan / Fotolia
Garden grass could become a source of cheap and clean renewable energy, scientists have claimed.

A team of UK researchers, including experts from Cardiff University's Cardiff Catalysis Institute, have shown that significant amounts of hydrogen can be unlocked from fescue grass with the help of sunlight and a cheap catalyst.

It is the first time that this method has been demonstrated and could potentially lead to a sustainable way of producing hydrogen, which has enormous potential in the renewable energy industry due to its high energy content and the fact that it does not release toxic or greenhouse gases when it is burnt.

Co-author of the study Professor Michael Bowker, from the Cardiff Catalysis Institute, said: "This really is a green source of energy.

"Hydrogen is seen as an important future energy carrier as the world moves from fossil fuels to renewable feedstocks, and our research has shown that even garden grass could be a good way of getting hold of it."

The team, which also includes researchers from Queen's University Belfast, have published their findings in the Royal Society journal Proceedings A.

Hydrogen is contained in enormous quantities all over in the world in water, hydrocarbons and other organic matter.

Up until now, the challenge for researchers has been devising ways of unlocking hydrogen from these sources in a cheap, efficient and sustainable way.

A promising source of hydrogen is the organic compound cellulose, which is a key component of plants and the most abundant biopolymer on Earth.

In their study, the team investigated the possibility of converting cellulose into hydrogen using sunlight and a simple catalyst -- a substance which speeds up a chemical reaction without getting used up.

This process is called photoreforming or photocatalysis and involves the sunlight activating the catalyst which then gets to work on converting cellulose and water into hydrogen.

The researchers studied the effectiveness of three metal-based catalysts -- Palladium, Gold and Nickel.

Nickel was of particular interest to the researchers, from a practical point of view, as it is a much more earth-abundant metal than the precious metals, and is more economical.

In the first round of experiments, the researchers combined the three catalysts with cellulose in a round bottom flask and subjected the mixture to light from a desk lamp. At 30 minutes intervals the researchers collected gas samples from the mixture and analysed it to see how much hydrogen was being produced.

To test the practical applications of this reaction, the researchers repeated the experiment with fescue grass, which was obtained from a domestic garden.

Professor Michael Bowker continued: "Up until recently, the production of hydrogen from cellulose by means of photocatalysis has not been extensively studied.

"Our results show that significant amounts of hydrogen can be produced using this method with the help of a bit of sunlight and a cheap catalyst.

"Furthermore, we've demonstrated the effectiveness of the process using real grass taken from a garden. To the best of our knowledge, this is the first time that this kind of raw biomass has been used to produce hydrogen in this way. This is significant as it avoids the need to separate and purify cellulose from a sample, which can be both arduous and costly."
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Source:
The above post is reprinted from materials provided by Cardiff University.

Reference:
A. Caravaca, W. Jones, C. Hardacre, M. Bowker. H2 production by the photocatalytic reforming of cellulose and raw biomass using Ni, Pd, Pt and Au on titania. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2016; 472 (2191): 20160054 DOI: 10.1098/rspa.2016.0054
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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
This conceptual diagram compares two approaches for modeling water movement above and below the land surface. Traditional land surface models simplify the system by solving it as a set of discrete columns without lateral groundwater flow while integrated hydrologic models connect three dimensional flow in the subsurface with processes at the land surface. Credit: Laura Condon, Syracuse, Mary Michael Forrester and Reed Maxwell, Colorado School of Mines
This conceptual diagram compares two approaches for modeling water movement above and below the land surface. Traditional land surface models simplify the system by solving it as a set of discrete columns without lateral groundwater flow while integrated hydrologic models connect three dimensional flow in the subsurface with processes at the land surface. Credit: Laura Condon, Syracuse, Mary Michael Forrester and Reed Maxwell, Colorado School of Mines
Groundbreaking research on global water supply co-authored by Colorado School of Mines Hydrology Professor Reed Maxwell and alumna Laura Condon, now assistant professor of civil and environmental engineering at Syracuse University, appears in the July 22 issue of Science Magazine.

The paper, "Connections between groundwater flow and transportation partitioning," tackles the issue of global freshwater supply by taking a unique approach in quantifying the water that plants release into the atmosphere through a process called transpiration in conjunction with evaporation of water from the soil. "Understanding how much fresh water we have on Earth seems like it should be an easy problem, but it's not," said Maxwell. "Since evaporation and transpiration often produce more water than surface flow from streams and rivers, this makes them very important for a fundamental understanding of seemingly basic questions like water flow."

Maxwell and Condon's model is unique because it integrates processes not often captured in existing water models, particularly the movement of water through the earth's subsurface, i.e. lateral groundwater flow, which can be contributed to both evaporation and transpiration. Through computer simulations of water flow across the continental US, the team found a significant increase in water supply from transpiration when including lateral groundwater flow. "This is one of our biggest findings," said Maxwell. "We see that disconnecting the groundwater movement from the simulation has a critical effect on matching other estimates of transpiration values."

The study's findings are paving the way for better global water models, which will greatly improve how scientists understand freshwater flows at continental scales. Groundwater flow seems to be the missing link in reconciling observations of plants' water usage with computer simulations, and may allow scientists to move towards a better understanding of how much freshwater is present on Earth.
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Source:
The above post is reprinted from materials provided by Colorado School of Mines.

Reference:
R. M. Maxwell, L. E. Condon. Connections Between Groundwater Flow and Transpiration Partitioning. Science, 2016 DOI: 10.1126/science.aaf7891
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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
A serpentinized rock specimen. Credit: NOAA Ocean Explorer.
A serpentinized rock specimen. Credit: NOAA Ocean Explorer.
Rocks formed beneath the ocean floor by fast-spreading tectonic plates may be a large and previously overlooked source of free hydrogen gas (H2), a new Duke University study suggests.

The finding could have far-ranging implications since scientists believe H2 might be the fuel source responsible for triggering life on Earth. And, if it were found in large enough quantities, some experts speculate that it could be used as a clean-burning substitute for fossil fuels today because it gives off high amounts of energy when burned but emits only water, not carbon.

Recent discoveries of free hydrogen gas, which was once thought to be very rare, have been made near slow-spreading tectonic plates deep beneath Earth's continents and under the sea.

"Our model, however, predicts that large quantities of H2 may also be forming within faster-spreading tectonic plates -- regions that collectively underlie roughly half of the Mid-Ocean Ridge," said Stacey L. Worman, a postdoctoral fellow at the University of Texas at Austin, who led the study while she was a doctoral student at Duke's Nicholas School of the Environment.

Total H2 production occurring beneath the oceans is at least an order of magnitude larger than production occurring under continents, the model suggests.

"A major benefit of this work is that it provides a testable, tectonic-based model for not only identifying where free hydrogen gas may be forming beneath the seafloor, but also at what rate, and what the total scale of this formation may be, which on a global basis is massive," said Lincoln F. Pratson, professor of earth and ocean sciences at Duke, who co-authored the study.

The scientists published their peer-reviewed study in the July 14 online edition of the journal Geophysical Research Letters.

The new model calculates the amount of free hydrogen gas produced and stored beneath the seafloor based on a range of parameters -- including the ratio of a site's tectonic spreading rate to the thickness of serpentinized rocks that might be found there.

Serpentinized rocks -- so called because they often have a scaly, greenish-brown-patterned surface that resembles snakeskin -- are rocks that have been chemically altered by water as they are lifted up by the spreading tectonic plates in Earth's crust.

Molecules of free hydrogen gas are produced as a by-product of the serpentinization process.

"Most scientists previously thought all hydrogen production occurs only at slow-spreading lithosphere, because this is where most serpentinized rocks are found. Although faster-spreading lithosphere contains smaller quantities of this rock, our analysis suggests the amount of H2 produced there might still be large," Worman said.

"Right now, the only way to get H2 -- to use in fuel cells, for example -- is through secondary processes," Worman explained. "You start with water, add energy to split the oxygen and hydrogen molecules apart, and get H2. You can then burn the H2, but you had to use energy to get energy, so it's not very efficient."

Mining free hydrogen gas as a primary fuel source could change that, but first scientists need to understand where the gas goes after it's produced. "Maybe microbes are eating it, or maybe it's accumulating in reservoirs under the seafloor. We still don't know," Worman said. "Of course, such accumulations would have to be quite significant to make hydrogen gas produced by serpentinization a viable fuel source."

If further research confirms the model's accuracy, it could also open new avenues for exploring the origin of life on Earth, and for understanding the role hydrogen gas might play in supporting life in a wide range of extreme environments, from the sunless deep-sea floor to distant planets.

Worman and Pratson conducted the study with Jeffrey Karson, professor of earth sciences at Syracuse University, and Emily Klein, professor of earth sciences at Duke.

Worman received her Ph.D. in earth and ocean sciences from Duke in 2015.
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Source:
The above post is reprinted from materials provided by Duke University.

Reference:
Stacey L. Worman, Lincoln F. Pratson, Jeffrey A. Karson, Emily M. Klein. Global rate and distribution of H2gas produced by serpentinization within oceanic lithosphere. Geophysical Research Letters, 2016; 43 (12): 6435 DOI: 10.1002/2016GL069066
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