Tag Archives: Superconductors

Seaweed For Making Superconductors and Supercapacitors

Seaweed, a kind of algae, and a part of cuisines in many parts of the world could be worked to supply power to electronics and other devices. Researchers have developed a material from seaweed to produce better superconductors, batteries, and fuel cells.

The research has been presented at a meeting of the American Chemical Society (ACS) on April 5, 2017.

Dongjiang Yang, PhD, a team member explains that carbon rich materials offer the most efficient energy storage solutions. Since the team wanted to use a green method for making superconductors, they chose seaweed, which is highly renewable as the base material. The scientists have intended to use seaweed extract as a template for fabricating a chain of porous materials that could be used to build the superconductors and energy storage solutions.

Although conventional carbon materials like graphite and graphene dominate the prevalent energy scenario, upcoming advances in storage devices could call for more sustainable materials. Yang, who is at Qingdao University in China, says that abundantly available seaweed could provide a more lasting solution in this regard. He has worked with colleagues in Griffith University in Australia and in Los Alamos National Laboratory in the US to devise a special kind of structure from the algae.

Egg-Box Structure

The scientists drew out porous carbon nanofibers from the seaweed extract by the process of chelating or binding. This process involved attaching cobalt ions to the alginate molecules of the seaweed. These molecules enveloped the cobalt metallic ions, which resulted in the formation of the nanofibers with a special structure resembling an egg-box. This structure contributes to the stability of the material so that the synthesis can be controlled.

Wide Range of Functions

Tests performed on the material showed that its reversible capacity is very high, around 625 mA hours per gram. This is much more than 372 mA hours per gram, which is the corresponding value for that of traditional graphite anodes used in lithium ion batteries.

Furthermore, the material performed as an efficient superconductor with a capacitance as high as 197 Farads per gram. This could be exploited in supercapacitors and zinc-air batteries. Tests also revealed that the performance of these egg-box nanofibers is as good as platinum-based catalysts used in fuel cells.

The scientists had first made public their findings on the egg-box structure in 2015. Since then they have been upgrading the technology involved. It is expected that there would be further improvements of the material.

For instance, the researchers explain that they have worked on the egg-box structure to reduce certain flaws in the seaweed structure that increased the motion of lithium ions. This helped to fabricate improved cathodes used in lithium ion batteries enhancing the performance.

In a more recent development, the researchers have forwarded a technique by which they have combined carrageenann, a variety derived from red algae with iron to prepare a carbon aerogel doped with sulfur. It has a very porous surface making for an extremely large surface area. The researchers say that this could be used very effectively in supercapacitors and in lithium sulfur batteries.

The researchers are now working towards commercial production of the seaweed-based devices.

Superconductivity Temperatures Get Higher

Superconductors have the capability and the potential to revolutionize our lives through improved technology. That includes superior thermal conductivity, remarkable magnetic properties and nearly zero electrical resistance. However, all that is only possible at cryogenic temperatures, that is, at temperatures in the region of absolute zero, at -273°C or -459°F.

Researchers at the Johannes Gutenberg University Mainz and the Max Plank Institute for Chemistry are working on material, which will work as superconductors equally well at room temperature. They have developed a record high-temperature superconductor, but it smells like rotten eggs.

Although superconductors are useful in all aspects of life – from fusion reactors to MRI scanners, the major deterrent is they work below -234°C or -389°F, which rather limits their application. Although all engineers want is superconductors that work at room temperatures, until now, the best they had is cuprates or copper oxide ceramics working under normal pressures at -140°C (-220°F) or under high pressures at -109°C (-164°F).

The team led by the Max Plank Institute is using H2S or Hydrogen Sulphide as the new record-holder. Although a colorless gas, H2S is usually associated with the smell emanating from rotten eggs. The team has found that H2S, when cooled and subjected to high pressures, acts like a superconductor. The super high-pressure chamber consists of a cryogenic cell of dimensions one-cubic centimeter placed between two flat-faced diamonds.

The super-cooled liquefied hydrogen sulphide placed in the cryogenic cell is subjected to high pressure by squeezing the two diamond faces together. As the pressure reaches 1.5 megabars, the super-cooled liquid H2S becomes a superconductor. This happens at a record new high temperature of -70°C or -94°F.

Scientists placed electrodes in one of two identical cells to measure the electrical resistance and magnetic sensors in the other to measure the magnetic response of the super-cooled liquid. With this arrangement, they were able to arrive at the exact combination of pressure and temperature that caused the liquid to transition to superconductivity.

According to the team, H2S under pressure transforms to H3S, which contributes to the superconductivity. They explained the relatively high temperature of the superconductor to be mainly because of the presence of hydrogen atoms in the compound. Among all elements, hydrogen has the highest frequency of oscillations. As the gas solidifies under high pressure, it causes crystal lattices to form with strong atomic bonds in the molecule, transforming the gas to solid H3S.

The team is now setting their sights to producing superconductors with still higher transition temperatures. In their opinion, this will mean increasing the pressure to at least twice that used in their current experiment. That may also mean they will no longer be able to use H2S and instead have to use other substances such as pure hydrogen or compounds such as hydrogen rich polymers. With the latter, superconductivity may be possible at high temperatures but without the accompanying necessity for high pressure.

Head of the working group, Mikhael Eremets feels that other material may have a lot of potential for performing as conventional superconductors at high temperatures. While theoretically, there is no limit for conventional superconductors to achieve transition temperatures, the experiments conducted by the team give adequate reasons to hope that superconductivity at room temperatures can be a reality.