Cool Storage: New Ways to Stockpile Energy

By Richard Harth
 New Ways to Stockpile Energy
This schematic is of a 3-D supercapacitor utilizing graphene sheets studded with nano-oxide islands.

According to Leon Shaw, the Rowe Family Endowed Chair in Sustainable Energy at IIT, innovations at the submicroscopic level may help to satisfy society’s mountain-sized demands for energy. Rather than hunting for new sources of energy, Shaw focuses on an equally vexing challenge: energy storage.

In a pair of new projects funded by the National Science Foundation, Shaw applies nanotechnology techniques to store energy in two ways: through electrical charge in a device known as a supercapacitor, and chemically as hydrogen.

Hydrogen provides a versatile, clean, and safe energy source, free of harmful emissions. “One of the key issues is how we can store hydrogen in a compact manner as the energy source for fuel cells and use this green technology to compete with an internal combustion engine,” Shaw says, describing one of the hurdles on the path to a hydrogen economy.

One way to achieve this is to dissolve hydrogen molecules on the surface of a specialized material—ideally, one with a very high surface area. Shaw’s approach involves mixing two lightweight materials—lithium borohydride and magnesium hydride—at nanometer scale. “The [scientific] community has been thinking of mixing these two together for the last 10 years, but nobody could achieve it,” Shaw says.

Once lithium borohydride and magnesium hydride nanoparticles are combined, the available surface area for hydrogen storage becomes enormous and the release and uptake of hydrogen can occur very rapidly, at a temperature near 150 degrees Celsius (302 degrees Fahrenheit), which Shaw considers nearly ideal.

The released hydrogen from the nanoscale lithium borohydride and magnesium hydride mixture supplies useable energy to the fuel cell during driving. At a refueling station, hydrogen could be pumped back into the storage tank, returning the chemicals inside to the nanoscale lithium borohydride and magnesium hydride mixture. After rapid hydrogen refueling, the car is ready to drive for another 300 miles.

Storing large amounts of energy in a limited volume is also a central concern for electric vehicles, which have already entered the market ahead of their hydrogen-fueled competitors. While lithium-ion batteries, such as those used in the Nissan Leaf, have high energy densities (the amount of energy stored in a given system per unit volume), they require recharging for several hours after a drive of approximately 100 miles.

An alternative is the supercapacitor, which can recharge quickly from a matter of seconds to a few minutes. Most supercapacitors, however, are too low in energy density to be practical for vehicles. Shaw’s version uses graphene studded with nano-oxide islands having exceptional surface area. The new design integrates lithium ions onto the nano-oxide surface (with the graphene serving as the electronic conductor) and alters the electrode configuration, forming a 3-D supercapacitor with very high energy density. Shaw’s group has recently patented the technology.

“Once the supercapacitor becomes equivalent to the lithium-ion battery in energy density, you can drive for 100 miles and your charge time is reduced to five minutes,” Shaw says. “Then the whole thing suddenly becomes very practical.”

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Leon Shaw homepage:

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