Power/Performance Bits: May 28

Archival storage; potassium-oxygen battery.


Archival storage

Researchers at Harvard University and Northwestern University propose a method of long-lived archival data storage using low-weight molecules.

DNA has been explored as a method of archival storage, but the researchers argue that it is inadequate, as the DNA macromolecule is large and requires skilled, repetitive labor to encode and read.

Instead, the researchers turned to oligopeptides, a low-weight molecule consisting of two or more peptides bonded together, which are common, stable, and smaller than DNA, RNA or proteins.

“Think storing the contents of the New York Public Library with a teaspoon of protein,” said Brian Cafferty, a postdoctoral scholar at Harvard University. “At least at this stage, we do not see this method competing with existing methods of data storage. We instead see it as complementary to those technologies and, as an initial objective, well suited for long-term archival data storage.”

The team didn’t set out to borrow from biology, said Cafferty. “We instead relied on techniques common in organic and analytical chemistry, and developed an approach that uses small, low molecular weight molecules to encode information.”

Oligopeptides vary in mass, depending on their number and type of amino acids. The team created an array of microwells containing oligopeptides with varying masses and were able to ‘read’ them back using a mass spectrometer, which sorts the molecules by mass and thus tells them which oligopeptides are present or absent.

To translate the jumble of molecules into letters and words, they borrowed the binary code. An “M,” for example, uses four of eight possible oligopeptides, each with a different mass. The four floating in the well receive a “1,” while the missing four receive a “0.” The molecular-binary code points to a corresponding letter or, if the information is an image, a corresponding pixel.

With this method, a mixture of eight oligopeptides can store one byte of information, 32 can store four bytes, and so on.

Pairing molecule mass and binary code, the Whitesides team can “write” massive amounts of data. (Credit: Michael J. Fink / Harvard)

The team tested their method by writing and reading back physicist Richard Feynman’s famous lecture “There is plenty of room at the bottom,” a photo of Claude Shannon (known as the father of information theory), and Hokusai’s woodblock painting The Great Wave off Kanagawa.

While the team has been able to retrieve stored data with 99.9% accuracy, writing averages 8 bits per second and reading averages 20 bits per second. Current DNA storage techniques, while slower at writing, are faster at reading.

The researchers are optimistic, however, and say their approach can use any malleable molecule as long as it can be manipulated into distinguishable bits, potentially improving the stability, price, and capacity of their molecular storage with different classes of molecules. Their oligopeptides are custom-made and, therefore, more expensive. But future library builders could purchase inexpensive molecules (like alkanethiols) that would cost just one cent to record 100,000,000 bits of information.

While reading information back requires both specialized equipment and specialized experts, this is something the team touts as a benefit, as it makes it more difficult for stored data to be compromised if it must be accessed in person. However, the biggest benefit is the storage life. “Oligopeptides have stabilities of hundreds or thousands of years under suitable conditions,” the team said, and the molecules could persist without light or oxygen, in high heat and drought.

Potassium-oxygen battery

Researchers at Ohio State University developed a more reliable potassium-oxygen battery by improving the cathode. A major problem for these batteries is their short lifespan; they haven’t been able to recharge enough times to be cost-effective for grid or autonomous driving functions.

Potassium-oxygen batteries in the team’s early research never lasted longer than five or 10 charging cycles, due to oxygen contaminating the battery’s anode, causing it to break down. But by incorporating a conducting polymer into the cathode, the team was able to allow potassium ions to travel throughout the cathode, but restrict molecular oxygen from getting to the anode.

In the battery, air comes in through a fibrous carbon layer, then meets a second layer that is slightly less porous and finally ends at a third layer, which is barely porous at all. That third layer, made of the conducting polymer, allows potassium ions to travel throughout the cathode, but restricts molecular oxygen from getting to the anode.

The design means that the battery can be charged at least 125 times, giving potassium-oxygen batteries more than 12 times the longevity they previously had with low-cost electrolytes.

While the batteries have not been proven on the scale necessary for power-grid storage, the team says it shows potential and has the added benefit of not requiring cobalt, which is frequently mined in conflict zones or under duress. “It is very important that batteries intended for large-scale applications do not use cobalt,” said Vishnu-Baba Sundaresan, a professor of mechanical and aerospace engineering at Ohio State.

The potassium-oxygen battery is also cheaper than lithium-ion batteries, costing about $44 per kilowatt hour, compared to around $100 per kilowatt hour at the materials level for lithium-ion. “When it comes to batteries, one size does not fit all,” Sundaresan said. “For potassium-oxygen and lithium-oxygen batteries, the cost has been prohibitive to use them as grid power backup. But now that we’ve shown that we can make a battery this cheap and this stable, then it makes it compete with other technologies for grid power backup.”

Sundaresan added, “If you have a smallish battery that is cheap, then you can talk about scaling it up. If you have a smallish battery that is $1,000 a pop, then scaling it up is just not possible. This opens the door for scaling it up.”

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