Power/Performance Bits: Nov. 29

PV technology comparison

Joshua J. Romero at the IEEE Spectrum put together an overview of photovoltaic technologies, including the world records for each type of cell, grouped into five broad categories. There is a brief overview of each cell type and some of its trade-offs.

He also looks at how fast each technology has made efficiency gains. The most rapid progress is being seen in highly efficient but expensive and complex multijunction cells, and experimental, unstable perovskite and quantum dot technologies.

Flexible supercapacitors

A team of scientists at the University of Central Florida’s NanoScience Technology Center developed a new process for creating flexible supercapacitors that can store more energy and be recharged more than 30,000 times without degrading.

“If they were to replace the batteries with these supercapacitors, you could charge your mobile phone in a few seconds and you wouldn’t need to charge it again for over a week,” said Nitin Choudhary, a postdoctoral associate at UCF.

While supercapacitors are a tempting replacement for lithium-ion batteries, one capable of holding as much charge as a standard lithium-ion battery would have to be much larger.

To reduce size, the team experimented with applying two-dimensional transition-metal dichalcogenides (TMD), only a few atoms thick, to supercapacitors.

A thin, flexible supercapacitor developed at the University of Central Florida boasts high energy and power densities. (Source: University of Central Florida)

“There have been problems in the way people incorporate these two-dimensional materials into the existing systems – that’s been a bottleneck in the field. We developed a simple chemical synthesis approach so we can very nicely integrate the existing materials with the two-dimensional materials,” said principal investigator Yeonwoong “Eric” Jung, an assistant professor at UCF.

The team developed supercapacitors composed of millions of nanometer-thick wires coated with shells of 2D TMD tungsten disulfide. A highly conductive core facilitates fast electron transfer for fast charging and discharging. And uniformly coated shells of two-dimensional materials yield high energy and power densities.

Plus, because their supercapacitor is flexible, the team sees it as having applications for wearable technology. While they state it is not ready for commercialization, they are working with UCF’s Office of Technology Transfer to patent the new process.

Fluorescent dye for batteries

Scientists at the University at Buffalo identified a fluorescent dye called BODIPY, or boron-dipyrromethene, as an ideal material for stockpiling energy in rechargeable, liquid-based batteries.

The dye has unusual chemical properties that enable it to excel at two key tasks: storing electrons and participating in electron transfer. Batteries must perform these functions to save and deliver energy, and BODIPY is very good at them.

In experiments, a BODIPY-based test battery operated efficiently and with longevity, running well after the researchers drained and recharged it 100 times.

A glowing solution of BODIPY dye is swirled under a black light. A University at Buffalo study shows that the dye has interesting chemical properties that could make it an ideal material for use in large-scale rechargeable batteries. (Source: Douglas Levere/University of Buffalo)

“As the world becomes more reliant on alternative energy sources, one of the huge questions we have is, ‘How do we store energy?’ What happens when the sun goes down at night, or when the wind stops?” asked Timothy Cook, assistant professor of chemistry at Buffalo. “All these energy sources are intermittent, so we need batteries that can store enough energy to power the average house.”

As it turns out, BODIPY is a promising material for liquid-based redox flow batteries. Redox flow batteries consist of two tanks of fluids separated by various barriers.

When the battery is being used, electrons are harvested from one tank and moved to the other, generating an electric current that, in theory, could power devices as small as a flashlight or as big as a house. To recharge the battery, you would use a solar, wind or other energy source to force the electrons back into the original tank, where they would be available to do their job again.

For this experiment, the team filled both tanks of a redox flow battery with the same solution: a powdered BODIPY dye called PM 567 dissolved in liquid.

The BODIPY compounds displayed a notable quality: They were able to give up and receive an electron without degrading as many other chemicals do. This trait enabled the dye to store electrons and facilitate their transfer between the battery’s two ends during 100 cycles of charging and draining.

Based on the experiments, the scientists predict that BODIPY batteries would be powerful enough to be useful to society, generating an estimated 2.3 volts of electricity.