Power/Performance Bits: August 20

Rechargeable flow battery for cheaper, large-scale energy storage
In a creation that may eventually enable cheaper, large-scale energy storage, MIT researchers have engineered a new rechargeable flow battery that doesn’t rely on expensive membranes to generate and store electricity.

According to the researchers, the palm-sized prototype generates three times as much power per square centimeter as other membraneless systems — a power density they said is an order of magnitude higher than that of many lithium-ion batteries and other commercial and experimental energy-storage systems.

The device stores and releases energy in a device that relies on a phenomenon called laminar flow: Two liquids are pumped through a channel, undergoing electrochemical reactions between two electrodes to store or release energy. Under the right conditions, the solutions stream through in parallel, with very little mixing. The flow naturally separates the liquids, without requiring a costly membrane.

The reactants in the battery consist of a liquid bromine solution and hydrogen fuel. The researchers chose to work with bromine because the chemical is relatively inexpensive and available in large quantities.

In addition to bromine’s low cost and abundance, the chemical reaction between hydrogen and bromine holds great potential for energy storage. But fuel-cell designs based on hydrogen and bromine have largely had mixed results: Hydrobromic acid tends to eat away at a battery’s membrane, effectively slowing the energy-storing reaction and reducing the battery’s lifetime. To circumvent these issues, the team landed on a simple solution: Take out the membrane.

Contrary to previous opinions that membraneless systems are purely academic, this system could potentially have a large practical impact, the researchers pointed out.

While low-cost energy storage has the potential to foster widespread use of renewable energy, such as solar and wind power, to date such energy sources have been unreliable. Winds can be capricious, and cloudless days are never guaranteed but with cheap energy-storage technologies, renewable energy might be stored and then distributed via the electric grid at times of peak power demand.

By designing a flow battery without a membrane, the researchers were able to remove two large barriers to energy storage: cost and performance. Membranes are often the most costly component of a battery, and the most unreliable, as they can corrode with repeated exposure to certain reactants.

Working towards ‘plasmonic’ technologies
Purdue University researchers are working on a range of options to overcome a fundamental obstacle in commercializing plasmonic metamaterials that could bring advanced optical technologies for more powerful computers, new cancer treatments and other innovations.

The materials could make it possible to harness clouds of electrons called “surface plasmons” to manipulate and control light. Plasmonic materials under development now rely on the use of metals such as gold and silver, which absorb too much light for devices to be practical and are said to be “lossy” for this reason. They also are not compatible with the complementary metal–oxide–semiconductor (CMOS) manufacturing process used to construct integrated circuits.

But there are many alternative materials other than conventional metallic components that exhibit metallic properties and provide advantages in device performance, which range from specially “doped” semiconductors, to transparent electrically conductive oxides and ultrathin layers of carbon called graphene.

Plasmonic materials are promising for various potential advances, including more powerful microscopes; sensors; new types of light-harvesting systems for more efficient solar cells; computers and consumer electronics that use light instead of electronic signals to process information; cancer treatment; data storage; and even a cloak of invisibility.

Now, the researchers are working to replace silver and gold in materials that are created using two options: making semiconductors more metallic by adding metal impurities to them; or adding non-metallic elements to metals, in effect making them less metallic. Examples of these materials include zinc oxides and titanium nitride.

The researchers propose using titanium nitride instead of metals for the data-storage concept because it has a higher melting point than gold or silver, so it is especially promising for the technology, which works by using heat to record information on a magnetic disk. Unlike gold and silver, titanium nitride is CMOS compatible.

This graphic depicts a device created using “negatively refracting metamaterials” that could bring advances in applications including sensing, imaging, data storage, solar energy and optics. Purdue researchers are working on a range of options to overcome a fundamental obstacle in commercializing the materials. The small spheres at right represent a lattice of “meta-atoms” carefully designed and fabricated to produce a high-performance device. (Source: Birck Nanotechnology Center/Purdue University)

The researchers are especially excited about using the materials to enable the next generation of ultra-high-capacity computer hard drives as the heat-assisted magnetic recording drives promise far greater capacity than is possible with current technology.

 
~Ann Steffora Mutschler