Under pressure, sodium, hydrogen could undergo a metamorphosis, emerging as superconductor

ScienceDaily (June 13, 2011) — In the search for superconductors, finding ways to compress hydrogen into a metal has been a point of focus ever since scientists predicted many years ago that electricity would flow, uninhibited, through such a material.

Liquid metallic hydrogen is thought to exist in the high-gravity interiors of Jupiter and Saturn. But so far, on Earth, researchers have been unable to use static compression techniques to squeeze hydrogen under high enough pressures to convert it into a metal. Shock-wave methods have been successful, but as experiments with diamond anvil cells have shown, hydrogen remains an insulator even under pressures equivalent to those found in Earth's core.

To circumvent the problem, a pair of University at Buffalo chemists has proposed an alternative solution for metallizing hydrogen: Add sodium to hydrogen, they say, and it just might be possible to convert the compound into a superconducting metal under significantly lower pressures.

The research, published June 10 in Physical Review Letters, details the findings of UB Assistant Professor Eva Zurek and UB postdoctoral associate Pio Baettig.

Using an open-source computer program that UB PhD student David Lonie designed, Zurek and Baettig looked for sodium polyhydrides that, under pressure, would be viable superconductor candidates. The program, XtalOpt , is an evolutionary algorithm that incorporates quantum mechanical calculations to determine the most stable geometries or crystal structures of solids.

In analyzing the results, Baettig and Zurek found that NaH9, which contains one sodium atom for every nine hydrogen atoms, is predicted to become metallic at an experimentally achievable pressure of about 250 gigapascals -- about 2.5 million times Earth's standard atmospheric pressure, but less than the pressure at Earth's core (about 3.5 million atmospheres).

"It is very basic research," says Zurek, a theoretical chemist. "But if one could potentially metallize hydrogen using the addition of sodium, it could ultimately help us better understand superconductors and lead to new approaches to designing a room-temperature superconductor."

By permitting electricity to travel freely, without resistance, such a superconductor could dramatically improve the efficiency of power transmission technologies.

Zurek, who joined UB in 2009, conducted research at Cornell University as a postdoctoral associate under Roald Hoffmann, a Nobel Prize-winning theoretical chemist whose research interests include the behavior of matter under high pressure.

In October 2009, Zurek co-authored a paper with Hoffman and other colleagues in the Proceedings of the National Academy of Sciences predicting that LiH6 -- a compound containing one lithium atom for every six hydrogen atoms -- could form as a stable metal at a pressure of around 1 million atmospheres.

Neither LiH6 and NaH9 exists naturally as stable compounds on Earth, but under high pressures, their structure is predicted to be stable.

"One of the things that I always like to emphasize is that chemistry is very different under high pressures," Zurek says. "Our chemical intuition is based upon our experience at one atmosphere. Under pressure, elements that do not usually combine on the Earth's surface may mix, or mix in different proportions. The insulator iodine becomes a metal, and sodium becomes insulating. Our aim is to use the results of computational experiments in order to help develop a chemical intuition under pressure, and to predict new materials with unusual properties."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University at Buffalo.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Under pressure, sodium, hydrogen could undergo a metamorphosis, emerging as superconductor

ScienceDaily (June 13, 2011) — In the search for superconductors, finding ways to compress hydrogen into a metal has been a point of focus ever since scientists predicted many years ago that electricity would flow, uninhibited, through such a material.

Liquid metallic hydrogen is thought to exist in the high-gravity interiors of Jupiter and Saturn. But so far, on Earth, researchers have been unable to use static compression techniques to squeeze hydrogen under high enough pressures to convert it into a metal. Shock-wave methods have been successful, but as experiments with diamond anvil cells have shown, hydrogen remains an insulator even under pressures equivalent to those found in Earth's core.

To circumvent the problem, a pair of University at Buffalo chemists has proposed an alternative solution for metallizing hydrogen: Add sodium to hydrogen, they say, and it just might be possible to convert the compound into a superconducting metal under significantly lower pressures.

The research, published June 10 in Physical Review Letters, details the findings of UB Assistant Professor Eva Zurek and UB postdoctoral associate Pio Baettig.

Using an open-source computer program that UB PhD student David Lonie designed, Zurek and Baettig looked for sodium polyhydrides that, under pressure, would be viable superconductor candidates. The program, XtalOpt , is an evolutionary algorithm that incorporates quantum mechanical calculations to determine the most stable geometries or crystal structures of solids.

In analyzing the results, Baettig and Zurek found that NaH9, which contains one sodium atom for every nine hydrogen atoms, is predicted to become metallic at an experimentally achievable pressure of about 250 gigapascals -- about 2.5 million times Earth's standard atmospheric pressure, but less than the pressure at Earth's core (about 3.5 million atmospheres).

"It is very basic research," says Zurek, a theoretical chemist. "But if one could potentially metallize hydrogen using the addition of sodium, it could ultimately help us better understand superconductors and lead to new approaches to designing a room-temperature superconductor."

By permitting electricity to travel freely, without resistance, such a superconductor could dramatically improve the efficiency of power transmission technologies.

Zurek, who joined UB in 2009, conducted research at Cornell University as a postdoctoral associate under Roald Hoffmann, a Nobel Prize-winning theoretical chemist whose research interests include the behavior of matter under high pressure.

In October 2009, Zurek co-authored a paper with Hoffman and other colleagues in the Proceedings of the National Academy of Sciences predicting that LiH6 -- a compound containing one lithium atom for every six hydrogen atoms -- could form as a stable metal at a pressure of around 1 million atmospheres.

Neither LiH6 and NaH9 exists naturally as stable compounds on Earth, but under high pressures, their structure is predicted to be stable.

"One of the things that I always like to emphasize is that chemistry is very different under high pressures," Zurek says. "Our chemical intuition is based upon our experience at one atmosphere. Under pressure, elements that do not usually combine on the Earth's surface may mix, or mix in different proportions. The insulator iodine becomes a metal, and sodium becomes insulating. Our aim is to use the results of computational experiments in order to help develop a chemical intuition under pressure, and to predict new materials with unusual properties."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University at Buffalo.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New method to make sodium ion-based battery cells could lead to better, cheaper batteries for the electrical grid

ScienceDaily (June 8, 2011) — By adding the right amount of heat, researchers have developed a method that improves the electrical capacity and recharging lifetime of sodium ion rechargeable batteries, which could be a cheaper alternative for large-scale uses such as storing energy on the electrical grid.

To connect solar and wind energy sources to the electrical grid, grid managers require batteries that can store large amounts of energy created at the source. Lithium ion rechargeable batteries -- common in consumer electronics and electric vehicles -- perform well, but are too expensive for widespread use on the grid because many batteries will be needed, and they will likely need to be large. Sodium is the next best choice, but the sodium-sulfur batteries currently in use run at temperatures above 300 degrees Celsius, or three times the temperature of boiling water, making them less energy efficient and safe than batteries that run at ambient temperatures.

Battery developers want the best of both worlds -- to use both inexpensive sodium and use the type of electrodes found in lithium rechargeables. A team of scientists at the Department of Energy's Pacific Northwest National Laboratory and visiting researchers from Wuhan University in Wuhan, China used nanomaterials to make electrodes that can work with sodium, they reported June 3 online in the journal Advanced Materials.

"The sodium-ion battery works at room temperature and uses sodium ions, an ingredient in cooking salt. So it will be much cheaper and safer," said PNNL chemist Jun Liu, who co-led the study with Wuhan University chemist Yuliang Cao.

The electrodes in lithium rechargeables that interest researchers are made of manganese oxide. The atoms in this metal oxide form many holes and tunnels that lithium ions travel through when batteries are being charged or are in use. The free movement of lithium ions allows the battery to hold electricity or release it in a current. But simply replacing the lithium ions with sodium ions is problematic -- sodium ions are 70 percent bigger than lithium ions and don't fit in the crevices as well.

To find a way to make bigger holes in the manganese oxide, PNNL researchers went much much smaller. They turned to nanomaterials -- materials made on the nanometer-sized scale, or about a million times thinner than a dime -- that have surprising properties due to their smallness. For example, the short distances that sodium ions have to travel in nanowires might make the manganese oxide a better electrode in ways unrelated to the size of the tunnels.

To explore, the team mixed two different kinds of manganese oxide atomic building blocks -- one whose atoms arrange themselves in pyramids, and another one whose atoms form an octahedron, a diamond-like structure from two pyramids stuck together at their bases. They expected the final material to have large S-shaped tunnels and smaller five-sided tunnels through which the ions could flow.

After mixing, the team treated the materials with temperatures ranging from 450 to 900 degrees Celsius, then examined the materials and tested which treatment worked best. Using a scanning electron microscope, the team found that different temperatures created material of different quality. Treating the manganese oxide at 750 degrees Celsius created the best crystals: too low and the crystals appeared flakey, too high and the crystals turned into larger flat plates.

Zooming in even more using a transmission electron microscope at EMSL, DOE's Environmental Molecular Sciences Laboratory on PNNL's campus, the team saw that manganese oxide heated to 600 degrees had pockmarks in the nanowires that could impede the sodium ions, but the 750 degree-treated wires looked uniform and very crystalline.

But even the best-looking material is just window-dressing if it doesn't perform well. To find out if it lived up to its good looks, the PNNL-Wuhan team dipped the electrode material in electrolyte, the liquid containing sodium ions that will help the manganese oxide electrodes form a current. Then they charged and discharged the experimental battery cells repeatedly.

The team measured peak capacity at 128 milliAmp hours per gram of electrode material as the experimental battery cell discharged. This result surpassed earlier ones taken by other researchers, one of which achieved peak capacity of 80 milliAmp hours per gram for electrodes made from manganese oxide but with a different production method. The researchers think the lower capacity is due to sodium ions causing structural changes in that manganese oxide that do not occur or occur less frequently in the heat-treated nano-sized material.

In addition to high capacity, the material held up well to cycles of charging and discharging, as would occur in consumer use. Again, the material treated at 750 Celsius performed the best: after 100 cycles of charging-discharging, it lost only 7 percent of its capacity. Material treated at 600 Celsius or 900 Celsius lost about 37 percent and 25 percent, respectively.

Even after 1,000 cycles, the capacity of the 750 Celsius-treated electrodes only dropped about 23 percent. The researchers thought the material performed very well, retaining 77 percent of its initial capacity.

Last, the team charged the experimental cell at different speeds to determine how quickly it could take up electricity. The team found that the faster they charged it, the less electricity it could hold. This suggested to the team that the speed with which sodium ions could diffuse into the manganese oxide limited the battery cell's capacity -- when charged fast, the sodium ions couldn't enter the tunnels fast enough to fill them up.

To compensate for the slow sodium ions, the researchers suggest in the future they make even smaller nanowires to speed up charging and discharging. Grid batteries need fast charging so they can collect as much newly made energy coming from renewable sources as possible. And they need to discharge fast when demands shoots up as consumers turn on their air conditioners and television sets, and plug in their electric vehicles at home.

Such high performing batteries could take the heat off an already taxed electrical power grid.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Pacific Northwest National Laboratory.

Journal Reference:

Yuliang Cao, Lifen Xiao, Wei Wang, Daiwon Choi, Zimin Nie, Jianguo Yu, Laxmikant V. Saraf, Zhenguo Yang, Jun Liu. Reversible Sodium Ion Insertion in Single Crystalline Manganese Oxide Nanowires with Long Cycle Life. Advanced Materials, 2011; DOI: 10.1002/adma.201100904

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New method to make sodium ion-based battery cells could lead to better, cheaper batteries for the electrical grid

ScienceDaily (June 8, 2011) — By adding the right amount of heat, researchers have developed a method that improves the electrical capacity and recharging lifetime of sodium ion rechargeable batteries, which could be a cheaper alternative for large-scale uses such as storing energy on the electrical grid.

To connect solar and wind energy sources to the electrical grid, grid managers require batteries that can store large amounts of energy created at the source. Lithium ion rechargeable batteries -- common in consumer electronics and electric vehicles -- perform well, but are too expensive for widespread use on the grid because many batteries will be needed, and they will likely need to be large. Sodium is the next best choice, but the sodium-sulfur batteries currently in use run at temperatures above 300 degrees Celsius, or three times the temperature of boiling water, making them less energy efficient and safe than batteries that run at ambient temperatures.

Battery developers want the best of both worlds -- to use both inexpensive sodium and use the type of electrodes found in lithium rechargeables. A team of scientists at the Department of Energy's Pacific Northwest National Laboratory and visiting researchers from Wuhan University in Wuhan, China used nanomaterials to make electrodes that can work with sodium, they reported June 3 online in the journal Advanced Materials.

"The sodium-ion battery works at room temperature and uses sodium ions, an ingredient in cooking salt. So it will be much cheaper and safer," said PNNL chemist Jun Liu, who co-led the study with Wuhan University chemist Yuliang Cao.

The electrodes in lithium rechargeables that interest researchers are made of manganese oxide. The atoms in this metal oxide form many holes and tunnels that lithium ions travel through when batteries are being charged or are in use. The free movement of lithium ions allows the battery to hold electricity or release it in a current. But simply replacing the lithium ions with sodium ions is problematic -- sodium ions are 70 percent bigger than lithium ions and don't fit in the crevices as well.

To find a way to make bigger holes in the manganese oxide, PNNL researchers went much much smaller. They turned to nanomaterials -- materials made on the nanometer-sized scale, or about a million times thinner than a dime -- that have surprising properties due to their smallness. For example, the short distances that sodium ions have to travel in nanowires might make the manganese oxide a better electrode in ways unrelated to the size of the tunnels.

To explore, the team mixed two different kinds of manganese oxide atomic building blocks -- one whose atoms arrange themselves in pyramids, and another one whose atoms form an octahedron, a diamond-like structure from two pyramids stuck together at their bases. They expected the final material to have large S-shaped tunnels and smaller five-sided tunnels through which the ions could flow.

After mixing, the team treated the materials with temperatures ranging from 450 to 900 degrees Celsius, then examined the materials and tested which treatment worked best. Using a scanning electron microscope, the team found that different temperatures created material of different quality. Treating the manganese oxide at 750 degrees Celsius created the best crystals: too low and the crystals appeared flakey, too high and the crystals turned into larger flat plates.

Zooming in even more using a transmission electron microscope at EMSL, DOE's Environmental Molecular Sciences Laboratory on PNNL's campus, the team saw that manganese oxide heated to 600 degrees had pockmarks in the nanowires that could impede the sodium ions, but the 750 degree-treated wires looked uniform and very crystalline.

But even the best-looking material is just window-dressing if it doesn't perform well. To find out if it lived up to its good looks, the PNNL-Wuhan team dipped the electrode material in electrolyte, the liquid containing sodium ions that will help the manganese oxide electrodes form a current. Then they charged and discharged the experimental battery cells repeatedly.

The team measured peak capacity at 128 milliAmp hours per gram of electrode material as the experimental battery cell discharged. This result surpassed earlier ones taken by other researchers, one of which achieved peak capacity of 80 milliAmp hours per gram for electrodes made from manganese oxide but with a different production method. The researchers think the lower capacity is due to sodium ions causing structural changes in that manganese oxide that do not occur or occur less frequently in the heat-treated nano-sized material.

In addition to high capacity, the material held up well to cycles of charging and discharging, as would occur in consumer use. Again, the material treated at 750 Celsius performed the best: after 100 cycles of charging-discharging, it lost only 7 percent of its capacity. Material treated at 600 Celsius or 900 Celsius lost about 37 percent and 25 percent, respectively.

Even after 1,000 cycles, the capacity of the 750 Celsius-treated electrodes only dropped about 23 percent. The researchers thought the material performed very well, retaining 77 percent of its initial capacity.

Last, the team charged the experimental cell at different speeds to determine how quickly it could take up electricity. The team found that the faster they charged it, the less electricity it could hold. This suggested to the team that the speed with which sodium ions could diffuse into the manganese oxide limited the battery cell's capacity -- when charged fast, the sodium ions couldn't enter the tunnels fast enough to fill them up.

To compensate for the slow sodium ions, the researchers suggest in the future they make even smaller nanowires to speed up charging and discharging. Grid batteries need fast charging so they can collect as much newly made energy coming from renewable sources as possible. And they need to discharge fast when demands shoots up as consumers turn on their air conditioners and television sets, and plug in their electric vehicles at home.

Such high performing batteries could take the heat off an already taxed electrical power grid.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Pacific Northwest National Laboratory.

Journal Reference:

Yuliang Cao, Lifen Xiao, Wei Wang, Daiwon Choi, Zimin Nie, Jianguo Yu, Laxmikant V. Saraf, Zhenguo Yang, Jun Liu. Reversible Sodium Ion Insertion in Single Crystalline Manganese Oxide Nanowires with Long Cycle Life. Advanced Materials, 2011; DOI: 10.1002/adma.201100904

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Study evaluates relationship of urinary sodium with health outcomes

ScienceDaily (May 3, 2011) — In a study conducted to examine the health outcomes related to salt intake, as gauged by the amount of sodium excreted in the urine, lower sodium excretion was associated with an increased risk of cardiovascular death, while higher sodium excretion did not correspond with increased risk of hypertension or cardiovascular disease complications, according to a study in the May 4 issue of JAMA.

"Extrapolations from observational studies and short-term intervention trials suggest that population-wide moderation of salt intake might reduce cardiovascular events," according to background information in the article. "The assumption that lower salt intake would in the long run lower blood pressure, to our knowledge, has not yet been confirmed in longitudinal population-based studies."

Katarzyna Stolarz-Skrzypek, M.D., Ph.D., of the University of Leuven, Belgium, and colleagues examined the incidence of death, illness and hypertension in relation to measures of urinary sodium excretion. The study included 3,681 participants without cardiovascular disease (CVD) at the beginning of the study. Of these, 2,096 had normal blood pressure at baseline and 1,499 had blood pressure and sodium excretion measured at baseline and last follow-up (2005-2008).

The researches found that among 3,681 participants followed up for a median (midpoint) 7.9 years, cardiovascular deaths decreased across increasing tertiles (one of three groups) of 24-hour urinary sodium: from 50 deaths in the low (death rate, 4.1 percent), 24 deaths in the medium, (death rate, 1.9 percent) and 10 deaths in the high tertile (death rate, 0.8 percent). Analysis indicated that the risk of cardiovascular mortality was significantly elevated in the low tertile with a significant inverse association between cardiovascular mortality and tertile of sodium excretion. Baseline sodium excretion predicted neither total mortality nor fatal combined with nonfatal CVD events.

Among 2,096 participants followed up for 6.5 years, increasing tertiles of 24-hour urinary sodium were not associated with incidence of hypertension. In the entire hypertension cohort, across increasing tertiles of urinary sodium, the numbers of new cases of hypertension were 187 (27.0 percent) in the low, 190 (26.6 percent) in the medium, and 175 (25.4 percent) in the high sodium excretion group.

Among 1,499 participants followed up for 6.1 years, in multivariable-adjusted analyses, a 100-mmol increase in sodium excretion was associated with 1.71 mm Hg increase in systolic blood pressure but no change in diastolic BP.

"The associations between systolic pressure and sodium excretion did not translate into less morbidity or improved survival. On the contrary, low sodium excretion predicted higher cardiovascular mortality. Taken together, our current findings refute the estimates of computer models of lives saved and health care costs reduced with lower salt intake. They do also not support the current recommendations of a generalized and indiscriminate reduction of salt intake at the population level. However, they do not negate the blood pressure-lowering effects of a dietary salt reduction in hypertensive patients," the authors conclude.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by JAMA and Archives Journals.

Journal Reference:

Katarzyna Stolarz-Skrzypek, Tatiana Kuznetsova, Lutgarde Thijs, Valérie Tikhonoff, Jitka Seidlerová, Tom Richart, Yu Jin, Agnieszka Olszanecka, Sofia Malyutina, Edoardo Casiglia, Jan Filipovský, Kalina Kawecka-Jaszcz, Yuri Nikitin, Jan A. Staessen, for the European Project on Genes in Hypertension (EPOGH) Investigators. Fatal and Nonfatal Outcomes, Incidence of Hypertension, and Blood Pressure Changes in Relation to Urinary Sodium Excretion. JAMA, 2011; 305 (17): 1777-1785 DOI: 10.1001/jama.2011.574

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here