Biofilm makes energy from sweat + Low cost, sustainable alt to lithium-ion batteries

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The bacteria powering a truly green revolution in personal electronics

RELEASE: Researchers at the University of Massachusetts Amherst recently announced that they have figured out how to engineer a biofilm that harvests the energy in evaporation and converts it to electricity. This biofilm, which was announced in Nature Communications, has the potential to revolutionize the world of wearable electronics, powering everything from personal medical sensors to personal electronics.

“This is a very exciting technology,” says Xiaomeng Liu, graduate student in electrical and computer engineering in UMass Amherst’s College of Engineering and the paper’s lead author. “It is real green energy, and unlike other so-called ‘green-energy’ sources, its production is totally green.”

That’s because this biofilm—a thin sheet of bacterial cells about the thickness of a sheet of paper—is produced naturally by an engineered version of the bacteria Geobacter sulfurreducens. G. sulfurreducens is known to produce electricity and has been used previously in “microbial batteries” to power electrical devices. But such batteries require that G. sulfurreducens is properly cared for and fed a constant diet. By contrast, this new biofilm, which can supply as much, if not more, energy than a comparably sized battery, works, and works continuously, because it is dead. And because it’s dead, it doesn’t need to be fed.

“It’s much more efficient,” says Derek Lovley, Distinguished Professor of Microbiology at UMass Amherst and one of the paper’s senior authors. “We’ve simplified the process of generating electricity by radically cutting back on the amount of processing needed. We sustainably grow the cells in a biofilm, and then use that agglomeration of cells. This cuts the energy inputs, makes everything simpler and widens the potential applications.”

The secret behind this new biofilm is that it makes energy from the moisture on your skin. Though we daily read stories about solar power, at least 50% of the solar energy reaching the earth goes toward evaporating water. “This is a huge, untapped source of energy,” says Jun Yao, professor of electrical and computer engineering at UMass, and the paper’s other senior author. Since the surface of our skin is constantly moist with sweat, the biofilm can “plug-in” and convert the energy locked in evaporation into enough energy to power small devices.

“The limiting factor of wearable electronics,” says Yao, “has always been the power supply. Batteries run down and have to be changed or charged. They are also bulky, heavy, and uncomfortable.” But a clear, small, thin flexible biofilm that produces a continuous and steady supply of electricity and which can be worn, like a Band-Aid, as a patch applied directly to the skin, solves all these problems.

What makes this all work is that G. sulfurreducens grows in colonies that look like thin mats, and each of the individual microbes connects to its neighbors through a series of natural nanowires. The team then harvests these mats and uses a laser to etch small circuits into the films. Once the films are etched, they’re sandwiched between electrodes and finally sealed in a soft, sticky, breathable polymer that you can apply directly to your skin. Once this tiny battery is “plugged in” by applying it to your body, it can power small devices.

“Our next step is to increase the size of our films to power more sophisticated skin-wearable electronics,” says Yao, and Liu points out that one of the goals is to power entire electronic systems, rather than single devices.

Affordable and sustainable alternative to lithium-ion batteries proposed

RELEASE: Concerns regarding scarcity, high prices, and safety regarding the long-term use of lithium-ion batteries has prompted a team of researchers from Rensselaer Polytechnic Institute to propose a greener, more efficient, and less expensive energy storage alternative.

In research published recently in Proceedings of the National Academy of Sciences (PNAS), corresponding author Nikhil Koratkar, the John A. Clark and Edward T. Crossan Professor of Engineering at Rensselaer, and his team, assert that calcium ions could be used as an alternative to lithium-ions in batteries because of its abundance and low cost.

"The vast majority of rechargeable battery products are based on lithium-ion technology, which is the gold standard in terms of performance," said Dr. Koratkar. "However, the Achilles' heel for lithium-ion technology is cost. Lithium is a limited resource on the planet, and its price has increased drastically in recent years. We are working on an inexpensive, abundant, safe, and sustainable battery chemistry that uses calcium ions in an aqueous, water-based electrolyte."

While the larger size and higher charge density of calcium ions relative to lithium impairs diffusion kinetics and cyclic stability, Dr. Koratkar and his team offer oxide structures containing big open spaces (heptagonal and hexagonal channels) as a prospective solution. In their work, an aqueous calcium-ion battery is demonstrated using orthorhombic and trigonal polymorphs of molybdenum vanadium oxide (MoVO) as a host for calcium ions.

"The calcium ion is divalent, and hence one ion insertion will deliver two electrons per ion during battery operation," explains Dr. Koratkar. "This allows for a highly efficient battery with reduced mass and volume of calcium ions. However, the higher ionic charge and the larger size of calcium ions relative to lithium makes it very challenging to insert calcium ions into the battery electrodes. We overcome this problem by developing a special class of materials called molybdenum vanadium oxides that contain large hexagonal and heptagonal shaped channels or tunnels that run through the material."

The team demonstrated that calcium ions can be rapidly inserted and extracted from the material, with these tunnels acting as "conduits" for reversible and fast ion transport and the findings indicate that MoVO provides one of the best performances reported to date for the storage of calcium ions.

"Calcium-ion batteries might one day, in the not-so-distant future, replace lithium-ion technology as the battery chemistry of choice that powers our society," explains Dr. Koratkar. "This work can lead of a new class of high-performing calcium-based batteries that use Earth abundant and safe materials and are therefore affordable and sustainable. Such batteries could find widespread use in portable and consumer electronics, electric vehicles, as well as grid and renewable energy storage."
Kornee Offline
Regarding second article above: Noticing that not-so-low-cost Molybdenum and Vanadium were integral to the design, I checked for spot prices.
Both currently lower per kg than Lithium, but that may change drastically if there is mass uptake re batteries. Anyway that search led to noticing:
For some reason(s) there seems to be no EV uptake. Yet anyway.

I have already twice now posted regarding Sodium ion batteries as the touted front runner replacement for Lithium ones, and that tech is already well advanced.
But Chinese company CATL has probably cornered that segment via patents. As well as leading with new higher performance Lithium-Manganese etc. variant:
Clearly it's still a wide open field. The Calcium ion contender is though likely going to be a case of too little too late.
confused2 Offline
Re:The bacteria powering a truly green revolution in personal electronics

Isn't there a thing (Carnot cycle) where efficiency = (T_high-T_low)/T_high. For a person this looks like about (313-293)/313=0.033 or 3%. If a person is 100W this gives a possible whole body maximum of about 3W. I'm guessing the efficiency of converting sweat into electricity isn't going to be high (like very low). I tend to wash anything exposed to my sweat on roughly a monthly basis whether it needs it or not.

I'd say the future in personal electronics is in low power devices using either rechargeable or easily recyclable batteries. After some months with a smartphone (finally!) I'd say the amount of information I like to see is larger than I can conveniently carry around (compared with wallet). If wrapped around an arm the screen would still be too small. Needs to go direct into the brain. Thank you. But no.

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