Power/Performance Bits: Jan. 2

High-temp electronics; steam from the sun; Li-ion battery life.


High-temp electronics
Researchers at Purdue University, UC Santa Cruz, and Stanford developed a semiconducting plastic capable of operating at extreme temperatures. The new material, which combines both a semiconducting organic polymer and a conventional insulating organic polymer could reliably conduct electricity in up to 220 degrees Celsius (428 F).

“One of the plastics transports the charge, and the other can withstand high temperatures,” said Aristide Gumyusenge, a graduate researcher at Purdue. “When you blend them together, you have to find the right ratio so that they merge nicely and one doesn’t dominate the other.”

Not only does the material continue to conduct under extreme heat, its performance stays stable across a wide temperature range, making reliable operation possible under a range of circumstances.

A new organic plastic allows electronics to function in extreme temperatures without sacrificing performance. (Source: Purdue University / John Underwood)

“A lot of applications are limited by the fact that these plastics will break down at high temperatures, and this could be a way to change that,” said Brett Savoie, a professor of chemical engineering at Purdue. “Solar cells, transistors and sensors all need to tolerate large temperature changes in many applications, so dealing with stability issues at high temperatures is really critical for polymer-based electronics.”

Next, the team plans to further explore the material’s high and low temperature limits.

Steam from the sun
Engineers at MIT built a device capable of heating water above boiling with only the sun of a clear, bright day. The superheated steam from the device can sterilize medical equipment, be used in cooking and cleaning, heat industrial processes, or serve as distilled drinking water.

To avoid contamination in the source water, which caused problems in previous iterations, the device is suspended over a basin. The device is structured to absorb short-wavelength solar energy, which in turn heats up the device, causing it to reradiate this heat, in the form of longer-wavelength infrared radiation, to the water below. Interestingly, the researchers note that infrared wavelengths are more readily absorbed by water, versus solar wavelengths, which would simply pass right through.

For the device’s top layer, the team used a metal ceramic composite that is a highly efficient solar absorber. They coated the structure’s bottom layer with a material that easily and efficiently emits infared heat. Between these two materials, they sandwiched a layer of reticulated carbon foam, a sponge-like material studded with winding tunnels and pores, which retains the sun’s incoming heat and can further heat up the steam rising back up through the foam. The researchers also attached a small outlet tube to one end of the foam, through which all the steam can exit and be easily collected.

The entire setup was surrounded with a polymer enclosure to prevent heat from escaping.

In this experiment, the new steam-generating device was mounted over a basin of water, placed on a small table, and partially surrounded by a simple, transparent solar concentrator. The researchers measured the temperature of the steam produced over the course of the test day, Oct. 21, 2017. (MIT / Thomas Cooper et al.)

Under lab conditions that simulated the sunlight produced on a clear, sunny day, the device produced steam heated to 122 C. For further testing, the team constructed a simple solar concentrator to focus more light on the device. With this setup, under ambient conditions on an MIT building rooftop, a clear, bright day yielded steam in excess of 146 C over the course of 3.5 hours.

“It’s a completely passive system — you just leave it outside to absorb sunlight,” said Thomas Cooper, assistant professor of mechanical engineering at York University, who led the work as a postdoc at MIT. “You could scale this up to something that could be used in remote climates to generate enough drinking water for a family, or sterilize equipment for one operating room.”

Li-ion battery life
Researchers at Politecnico di Torino, University of Vienna, Université Laval, and the Institute for Basic Science in Korea developed a new nanostructured anode material that can extend the capacity and cycle life of lithium ion batteries.

The anode is a 2D/3D nanocomposite based on a mesoporous mixed metal oxide and graphene that enhances the electrochemical performance of the batteries.

An HRSEM picture of a 2D/3D nanocomposite based on graphene. (Source: © Freddy Kleitz/Universität Wien; Glaudio Gerbaldi/Politecnico di Torino)

To make the anode, the team mixed copper and nickel homogenously in a controlled manner to achieve the mixed metal. Based on nanocasting, a method used to produce mesoporous materials, they created structured nanoporous mixed metal oxide particles, which due to their extensive network of pores have a very high active reaction area for the exchange with lithium ion from the battery’s electrolyte. The scientists then applied a spray drying procedure to wrap the mixed metal oxide particles tightly with thin graphene layers.

“In our test runs, the new electrode material provided significantly improved specific capacity with unprecedented reversible cycling stability over 3,000 reversible charge and discharge cycles even at very high current regimes up to 1,280 milliamperes,” said Freddy Kleitz, head of the Department of Inorganic Chemistry – Functional Materials at the University of Vienna. Today’s lithium ion batteries lose their performance after about 1,000 charging cycles.

The team noted that the method used to make the anode is an environmentally friendly water-based process that is ready to be applied at an industrial level.

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