Research Bits: Oct. 10

Disposable water-activated battery

Researchers at Empa developed a water-activated disposable paper battery that could be used in low-power, single-use disposable electronics such as smart labels for tracking objects, environmental sensors, and medical diagnostic devices.

The battery is made of at least one cell measuring one centimeter squared and consisting of three inks printed onto a rectangular strip of paper. A salt, in this case sodium chloride (table salt), is dispersed throughout the strip of paper, and one of its shorter ends is dipped in wax. An ink containing graphite flakes, which acts as the cathode, is printed onto one of the flat sides of the paper while an ink containing zinc powder, which acts as the anode, is printed onto the reverse side of the paper. Another ink containing graphite flakes and carbon black is printed on both sides of the paper, on top of the other two inks. This ink makes up the current collectors connecting the positive and negative ends of the battery to two wires, which are located at the wax-dipped end of the paper.

The researchers explain the way the battery works: When a small amount of water is added, the salts within the paper dissolve and charged ions are released, thus making the electrolyte ionically conductive. These ions activate the battery by dispersing through the paper, resulting in zinc in the ink at the anode being oxidized thereby releasing electrons. By closing the external circuit these electrons can then be transferred from the zinc-containing anode via the graphite- and carbon black-containing ink to the graphite cathode where they are transferred to and hence reduce oxygen from ambient air. These redox reactions generate an electrical current that can be used to power an external electrical device.

The paper battery is composed of two electrochemical cells – at both ends of the paper strip – separated by a water barrier (between the letters “m” and “p”) and connected in series. (Credit: Empa)

To demonstrate the device, the team combined two cells into one battery to increase the operating voltage and used it to power an alarm clock with a liquid crystal display. Analysis of the performance of a one-cell battery revealed that after two drops of water were added, the battery activated within 20 seconds and, when not connected to an energy-consuming device, reached a stable voltage of 1.2 volts.

After one hour, the one-cell battery’s performance decreased significantly due to the paper drying. However, after the researchers added two extra drops of water, the battery maintained a stable operating voltage of 0.5 volts for more than one additional hour.

“What’s special about our new battery is that, in contrast many metal air batteries using a metal foil that is gradually consumed as the battery is depleted, our design allows to add only the amount of zinc to the ink that is actually needed for the specific application,” said Gustav Nyström of the Cellulose & Wood Materials Laboratory at Empa. The choice of paper and zinc also means the battery is biodegradable.

Parallelizing multi-language scripts

Researchers from MIT, University of Pennsylvania, XIV Staszic High School, Aarno Labs, and Stevens Institute of Technology propose a method to accelerate programs that run in the Unix shell without incurring errors. Called PaSh, the system aims to enable the parallelization of scripts written in multiple languages, allowing them to be run on multiple processors.

“When a program is written in a single language, developers have explicit information about its features and the language that helps them determine which components can be parallelized. But those tools don’t exist for scripts in the Unix shell. Users can’t easily see what is happening inside the components or extract information that would aid in parallelization,” said MIT News Office’s Adam Zewe. “To overcome this problem, PaSh uses a preprocessing step that inserts simple annotations onto program components that it thinks could be parallelizable. Then PaSh attempts to parallelize those parts of the script while the program is running, at the exact moment it reaches each component.”

“Unix shell scripts play a key role in data analytics and software engineering tasks. These scripts could run faster by making the diverse programs they invoke utilize the multiple processing units available in modern CPUs. However, the shell’s dynamic nature makes it difficult to devise parallel execution plans ahead of time,” said Diomidis Spinellis, a professor of software engineering at Athens University of Economics and Business and professor of software analytics at Delft Technical University, who was not involved with this research. “Through just-in-time analysis, PaSh-JIT succeeds in conquering the shell’s dynamic complexity and thus reduces script execution times while maintaining the correctness of the corresponding results.”

This “just-in-time” method of parallelization avoids trying to predict a program’s behavior ahead of time, and the researchers contend it is able to effectively speed up many more components than traditional methods that try to perform parallelization in advance. Zewe notes that it also ensures accurate results: “If PaSh arrives at a program component that cannot be parallelized (perhaps it is dependent on a component that has not run yet), it simply runs the original version and avoids causing an error.”

“There are so many people who use these types of programs, like data scientists, biologists, engineers, and economists. Now they can automatically accelerate their programs without fear that they will get incorrect results,” said Nikos Vasilakis, research scientist in the Computer Science and Artificial Intelligence Laboratory (CSAIL) at MIT. “No matter the performance benefits — if you promise to make something run in a second instead of a year — if there is any chance of returning incorrect results, no one is going to use your method.”

In testing on hundreds of scripts, PaSh did not break any and was able to run programs six times faster, on average. “Our system is the first that shows this type of fully correct transformation, but there is an indirect benefit, too. The way our system is designed allows other researchers and users in industry to build on top of this work,” Vasilakis added.

Moving forward, Vasilakis wants to use PaSh to tackle the problem of distribution — dividing a program to run on many computers, rather than many processors within one computer. He is also looking to improve the annotation scheme so it is more user-friendly and can better describe complex program components.

Room-temperature thermoelectrics

Researchers from KTH Royal Institute of Technology, University of Valencia, and University of Warwick developed a thermoelectric coating that can harvest energy from devices that operate around room temperature.

When one end of a thermoelectric material is heated up, charge carriers move away from the hot end towards the cold end, resulting in an electric current. The team’s hybrid thermoelectric materials work for devices that generate heat of less than 100°C and integrate solid state semiconductors with flexible materials such as polymers to formulate inks.

The coating can be applied to any surface that dissipates heat to generate electrical power, said Muhammet Toprak, professor of materials chemistry at KTH. “These results open a new low-cost and sustainable way of producing and implementing thermoelectric coatings on a large scale. In the short term, this is expected to make an impact for IoT and other low power applications. It could replace batteries by being integrated as a coating in the form of wearable electronics.”

Toprak added, “In the long run, with the use of more sustainable inorganic thermoelectric materials compositions and sustainable biopolymers, such as cellulose and lignocellulose (or plant matter), the use of this technology on large areas will impact the adaptation of thermoelectric technology for efficient heat-to-power energy harvesting, as a complementary means to green transition.”