Power/Performance Bits: Mar. 5

Solar chemical manufacturing; turning bags into batteries; low power digital PLL.


Solar chemical manufacturing
Researchers at RMIT University, CSIRO Manufacturing, and University of Melbourne developed a nano-enhanced material that can capture 99% of light and use it to power chemical reactions. One of the world’s biggest energy users, the chemical manufacturing industry accounts for about 10% of global energy consumption and 7% of industrial greenhouse gas emissions. In the US, chemical manufacturing uses more energy than any other industry, accounting for 28% of industrial energy consumption in 2017, according to the researchers.

While photo catalysis, or using light to drive chemical reactions, is growing, efficiency and cost are still barriers.

“Chemical manufacturing is a power hungry industry because traditional catalytic processes require intensive heating and pressure to drive reactions,” said Daniel Gomez, an associate professor at RMIT. “But one of the big challenges in moving to a more sustainable future is that many of the materials that are best for sparking chemical reactions are not responsive enough to light.”

The team focused on palladium, which while not very light responsive excels at producing chemical reactions. Manipulating the material’s optical properties made it more sensitive to light. Additionally, the technique uses only a tiny amount of the rare, expensive material. Just 4nm of nano-enhanced palladium is enough to absorb 99% of light and achieve a chemical reaction.

“The photo catalyst we’ve developed can catch 99% of light across the spectrum, and 100% of specific colours,” adds Gomez. “It’s scaleable and efficient technology that opens new opportunities for the use of solar power – moving from electricity generation to directly converting solar energy into valuable chemicals.”

The team also sees promise in the area of desalination: the material could be placed in salty water and generate enough energy to boil and evaporate it.

Turning bags into batteries
Researchers from Purdue University and Centro de Ingeniería y Desarrollo Industrial demonstrated a way to turn waste plastic bags into carbon anodes for lithium-ion batteries. In spite of efforts to reduce single-use plastics and increase recycling, approximately 60% of all plastics ever produced have been discarded and are accumulating in landfills or in the natural environment. Film plastic, which is typically not collected for curbside recycling and must be returned to a store or facility, likely fares even worse.

While ways to turn waste polyethylene into pure carbon have been researched for decades, the results have been inefficient or required expensive, complex processes.

In their new approach, the team focused on LDPE and HDPE, two common types of polyethylene used in plastic films such as food storage bags, trash bags, and retail sacks. After using samples of both types for general household use, the polyethylene plastic bags were immersed in sulfuric acid and sealed inside a solvothermal reactor, which heated the sample to just below polyethylene’s melting temperature.

At high temperatures polyethylene vaporizes into hazardous gases, but this treatment caused sulfonic acid groups to be added to the polyethylene carbon-carbon backbone, preventing that from happening. The sulfonated polyethylene was removed from the reactor and heated it in a furnace at 1600 degrees Fahrenheit in an inert atmosphere to produce pure carbon.

The team ground the carbon into a black powder and used it to make anodes for lithium-ion batteries. In tests, the resulting batteries performed comparably to commercial batteries.

Low power digital PLL
Scientists at Tokyo Institute of Technology developed an advanced digital phase-locked loop (PLL) frequency synthesizer they hope will drastically cut power consumption of IoT devices using Bluetooth Low Energy and other wireless technologies.

The fractional-N DPLL achieves a power consumption of only 265 microwatts (μW), less than half the lowest power consumption achieved to date (980 μW), according to the team.

Key to reducing overall power consumption was use of an automatic feedback system, said Kenichi Okada, associate professor at Tokyo Institute of Technology’s Department of Electrical and Electronic Engineering. “This automatic-switching feedback path consumes a power of 68 μW, which leads to a power consumption of 265 μW for the whole DPLL.”

Okada also noted that early experiments indicate the DPLL could extend battery life of low power IoT devices by four times.

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