Power/Performance Bits: Feb. 21

Harvesting energy from multiple sources

Researchers from the University of Oulu in Finland found a particular type of perovskite, KBNNO, has the right properties to extract energy from multiple sources simultaneously.

While perovskites are particularly known for their use as solar cells, certain minerals in the perovskite family show piezoelectric and pyroelectric (harvesting energy from temperature changes) properties.

When ferroelectric materials like KBNNO undergo changes in temperature, their dipoles misalign, which induces an electric current. Electric charge also accumulates according to the direction the dipoles point. Deforming the material causes certain regions to attract or repel charges, again generating a current.

Previous studies of KBNNO’s photovoltaic and general ferroelectric properties took place at temperatures a couple hundred degrees below freezing and didn’t focus on properties related to temperature or pressure. The new research is the first time all of these properties have been evaluated at once above room temperature, according to the team.

The experiments showed that while KBNNO is reasonably good at generating electricity from heat and pressure, it isn’t quite as good as other perovskites. However, the researchers found they could modify the composition of KBNNO to improve its pyroelectric and piezoelectric properties. “It is possible that all these properties can be tuned to a maximum point,” said Yang Bai, research fellow at Oulu.

The team is already exploring such an improved material by preparing KBNNO with sodium. The fabrication process is straightforward, noted Bai, who hopes to build a prototype multi-energy-harvesting device within the next year.

Superdense coding for data transfer

Researchers at the Department of Energy’s Oak Ridge National Laboratory set a new record in the transfer of information via superdense coding, a process by which the properties of particles like photons, protons and electrons are used to store as much information as possible.

The ORNL team transferred 1.67 bits per qubit, or quantum bit, over a fiber optic cable, edging out the previous record of 1.63 per qubit.

Qubits can employ two states simultaneously and therefore represent more information than a traditional bit. The physics of this quantum communication task employed by Williams and his team is similar to that used by quantum computers, which use qubits to arrive at solutions to extremely complex problems faster than their bit-laden counterparts.

The team transmitted the ORNL logo, an oak leaf, between two end points in the laboratory with 87 percent calculated fidelity. (Left): The original 4-color, 3.4kB image. (Right): The image received using superdense coding. (Source: ORNL)

The team used conventional laboratory equipment such as common fiber optic cable and standard photon detectors, bringing the technique one step closer to practical use.

While the technology is at present largely experimental, practical applications could include a cost-effective way to condense and transfer information. “This experiment demonstrates how quantum communication techniques can be integrated with conventional networking technology,” said Brian Williams of ORNL. “It’s part of the groundwork needed to build future quantum networks that can be used for computing and sensing applications.”

Low-cost grid battery

Chemists at Stanford University developed a battery made with urea as the electrolye, commonly found in fertilizers and mammal urine, which they say could offer a low-cost way to store renewable power.

The battery is nonflammable and contains electrodes made from aluminum and graphite. Its electrolyte’s main ingredient, urea, is already industrially produced by the ton for plant fertilizers.

“So essentially, what you have is a battery made with some of the cheapest and most abundant materials you can find on Earth. And it actually has good performance,” said Hongjie Dai, a Stanford chemistry professor. “Who would have thought you could take graphite, aluminum, urea, and actually make a battery that can cycle for a pretty long time?”

Grid storage is the team’s main goal, because of the battery’s low cost, high efficiency and long cycle life.

In particular, the battery shows excellent Coulombic efficiency, the measurement of how much charge exits the battery per unit of charge that it takes in during charging. The Coulombic efficiency for this battery was 99.7%. As far as cycle life, the urea-based aluminum ion batteries went through through about 1,500 charge cycles with a 45-minute charging time in the lab.

The battery is about 100 times cheaper than the rechargeable aluminum battery built by the group in 2015, thanks to the electrolyte.

A commercial version of the battery is currently in development.