Newly discovered enzyme that turns air into electricity, providing a new clean source of energy
by Monash University / March 8, 2023
“Australian scientists have discovered an enzyme that converts air into energy. The finding, published today in the journal Nature, reveals that this enzyme uses the low amounts of the hydrogen in the atmosphere to create an electrical current. This finding opens the way to create devices that literally make energy from thin air. The research team, led by Dr. Rhys Grinter, Ph.D. student Ashleigh Kropp, and Professor Chris Greening from the Monash University Biomedicine Discovery Institute in Melbourne, Australia, produced and analyzed a hydrogen – consuming enzyme from a common soil bacterium.
Recent work by the team has shown that many bacteria use hydrogen from the atmosphere as an energy source in nutrient-poor environments. “We’ve known for some time that bacteria can use the trace hydrogen in the air as a source of energy to help them grow and survive, including in Antarctic soils, volcanic craters, and the deep ocean” Professor Greening said. “But we didn’t know how they did this, until now.”
In this Nature paper, the researchers extracted the enzyme responsible for using atmospheric hydrogen from a bacterium called Mycobacterium smegmatis. They showed that this enzyme, called Huc, turns hydrogen gas into an electrical current. Dr. Grinter notes, “Huc is extraordinarily efficient. Unlike all other known enzymes and chemical catalysts, it even consumes hydrogen below atmospheric levels—as little as 0.00005% of the air we breathe.” The researchers used several cutting-edge methods to reveal the molecular blueprint of atmospheric hydrogen oxidation.
They used advanced microscopy (cryo-EM) to determine its atomic structure and electrical pathways, pushing boundaries to produce the most resolved enzyme structure reported by this method to date. They also used a technique called electrochemistry to demonstrate the purified enzyme creates electricity at minute hydrogen concentrations. Laboratory work performed by Kropp shows that it is possible to store purified Huc for long periods. “It is astonishingly stable. It is possible to freeze the enzyme or heat it to 80 degrees celsius, and it retains its power to generate energy,” Kropp said. “This reflects that this enzyme helps bacteria to survive in the most extreme environments. ”
Huc is a “natural battery” that produces a sustained electrical current from air or added hydrogen. While this research is at an early stage, the discovery of Huc has considerable potential to develop small air-powered devices, for example as an alternative to solar-powered devices. The bacteria that produce enzymes like Huc are common and can be grown in large quantities, meaning we have access to a sustainable source of the enzyme. Dr. Grinter says that a key objective for future work is to scale up Huc production. “Once we produce Huc in sufficient quantities, the sky is quite literally the limit for using it to produce clean energy.”
More information: Chris Greening, Structural basis for bacterial energy extraction from atmospheric hydrogen, Nature (2023). DOI: 10.1038/s41586-023-05781-7
Newly Discovered Photosynthesis ‘Leak’ Means More Juice
by Eric Mack / April 4, 2023
“Scientists have studied photosynthesis in plants for centuries, but an international team now believes it has unlocked new secrets in nature’s great machine that could revolutionize sustainable fuels and fight climate change. The team says it’s determined that it’s possible to extract an electrical charge at the best possible point in photosynthesis. This means harvesting the maximum amount of electrons from the process for potential use in power grids and some types of batteries. It could also improve the development of biofuels.
While it’s still early days, the findings, reported in the journal Nature, could reduce greenhouse gasses in the atmosphere and provide insights to improve photovoltaic solar panels. The key breakthrough came when researchers observed the process of photosynthesis at ultrafast timescales. “We can take photos at different times which allow us to watch changes in the sample really, really quickly — a million billion times faster than your iPhone,” Tomi Baikie, from the University of Cambridge’s Cavendish Laboratory, told CNET. The team used a technique called ultrafast transient absorption spectroscopy, which can be most simply understood as lighting up a sample with laser pulses and recording what happens at extremely short intervals. This makes it possible to watch electrons as they move through the entire photosynthetic process.
Previous demonstrations connected cyanobacteria, algae and other plants to electrodes to create so-called bio-photoelectrochemical cells that tap into the photosynthetic process to generate electricity. Baikie said the researchers were surprised to discover a previously unknown pathway of energy flow at the beginning of the process that could enable extracting the charge in a more efficient way. “We rely on plants for everything we eat and all the air that we breathe, and maybe we can also use their electrons too.” The scientists found that the place in the cell where photosynthesis starts was “leaking” electrons. In nature, this could protect plants from the harmful parts of sunlight. The discovery of the new, leaky pathway could also have major implications for the production of renewable biofuels, typically derived from plants or algae.
Biofuels can be carbon neutral because they both take up carbon dioxide when the plants are grown and release it back into the atmosphere when burned, versus fossil fuels that release carbon that’s been stored deep in the Earth for eons. How much carbon biofuel adds or subtracts from the atmosphere depends on how the plants are grown and how the fuel is produced. This research could be used to develop more-efficient processes for creating biofuels.
“It’s a completely new approach to biofuel production. We are gathering electrons from the most early and powerful points of photosynthesis and rerouting them there,” research coordinator Jenny Zhang, also from Cambridge, said via email. Zhang says others have attempted to harvest electrons from an earlier point in the photosynthetic process but concluded it was impossible. She says that at first, the team was convinced it had made a mistake. “It took a while for us to convince ourselves that we’d done it,” Zhang said in a statement.
The breakthrough essentially promises to harness more of the incredible efficiency of photosynthesis when it comes to turning sunlight into energy. “What makes photosynthesis really special is its near 100% efficiency in converting light to electrons,” Baikie explained. “By us understanding the mechanisms of photosynthesis, we can use this knowledge to inspire us to improve existing solar cell technology.” In addition to producing energy more efficiently, fine-tuning photosynthesis could also allow for the use of plants to better take up and store carbon dioxide, helping to fight human-caused climate change in the process.
Zhang imagines a future in which tapping into photosynthesis allows us to “farm our energy the way we farm our food” but doing so via organisms like cyanobacteria, which won’t require competing with food production. In fact, she said, the new insights gleaned from this research could give crops a boost by making them more tolerant to intense sunlight. “In the long run, if we can generate renewable energy and fuels from self-generating, self-recycling, living materials, it would be one of the greenest options one can imagine going forwards for sustainability.”
“Transistors inside modern computer chips are several nanometers across, and switch on and off at hundreds of gigahertz. Organic electrochemical transistors, made for biodegradable applications, are milimeters in size and switch at kilohertz rates. The world’s first wooden transistor, made by a collaboration of researchers through the Wallenberg Wood Science Center and reported this week in Publications of the National Academy of Sciences, is 3 centimeters across and switches at less than one hertz.
While it may not be powering any wood-based supercomputers anytime soon, it does hold out promise for specialized applications including biodegradable computing and implanting into living plant material. “It was very curiosity-driven,” says Isak Engquist, a professor at Linköping University, in Sweden, who led the effort. “We thought, ‘Can we do it? Let’s do it, let’s put it out there to the scientific community and hope that someone else has something where they see these could actually be of use in reality.’” Even though the wooden transistor still awaits its killer app, the idea to build wood-based electronics is not as crazy as it sounds.
A recent review of wood-based materials says, “Around 300 million years of tree evolution has yielded over 60,000 woody species, each of which is an engineering masterpiece of nature.” Wood has great structural stability while being highly porous and able to efficiently transport water and nutrients. The researchers leveraged these properties to create conducting channels inside the wood’s pores and electrochemically modulate their conductivity with the help of a penetrating electrolyte. Of the 60,000 species, the team chose balsa wood for its strength, even when one of the components of its structure—lignin—was largely removed to make more room for conducting materials.
To remove much of the lignin, pieces of balsa wood were treated with heat and chemicals for 5 hours. Then, the remaining cellulose-based structure was coated with a conducting polymer. The team tried several polymers, but they found one known as PEDOT:PSS to be the most effective, in part because it’s water soluble. Since the pores inside wood are made for transporting water, the PEDOT:PSS solution readily spread through the tubes. Electron microscopy and X-ray imaging of the result revealed that the polymer decorated the insides of the tube structures. The resulting wood chunks conducted electricity along their fibers.
To assemble a transistor, the researchers used three pieces of conducting wood, each 3 centimeters in length and several millimeters in height and width, arranged in a T shape. The top of the T served as the transistor channel, with a source on one end and a drain on the other. The channel was sandwiched between two “gate” pieces, forming the leg of the T. At the points of contact between the channel and the gates, the researchers layered a gel electrolyte. A voltage applied to the gates delivers hydrogen ions from the electrolyte into the polymer, causing a chemical reaction that changes the conductivity of the polymer.
This reaction is reversible, allowing for the on-off operation of this wood-based transistor. This was a proof-of-principle effort and, Engquist says, higher currents and smaller devices should be possible to engineer. Even still, it is unlikely to serve as the basis for complex electronics. However, it may find uses as an on/off switch for other components, such as solar cells, batteries, or sensors, that may be incorporated into wood, dead or living. “I have colleagues who are at the forefront in a field we call electronic plants,” Enquist says, “and they try to integrate electronic functionality into living plants. We have worked with deadwoods for this project, but the next step might be to integrate it also into living plants.”
A potential advantage of the wooden transistor is that it’s self-supporting: It does not require a substrate to be printed or deposited onto. Manufacturers of organic electrochemical transistors—versatile devices that are heavily researched for biosensing and bioelectronics applications—strive to make them from sustainable materials. Yet they still require glass or other substrates that are not sustainably sourced. “If we really do move to renewable or forest-based or bio-based materials, not just as an additive but as the actual structural components of the device,” says Daniel Simon, a professor of bioelectronics at Linköping University who was not involved in the work, “I think this opens up a really interesting space. This is really just the beginning, I believe.”
That said, these applications are still hypothetical, and the work, the researchers say, was done in the spirit of collaborative curiosity. “What was really important in this project was that we were very cross-disciplinary,” Engquist says. “We would not have a chance to have done this without the wooden-cellulose experts. And they, on the other hand, would never have thought of incorporating transistors into the wood that they are expertly treating in so many different ways. So it was only when we came together that we were able to do this, and I hope very much that that kind of collaboration in other places will find a use for what we have been doing here.”
VOLTAGE from WOOD
OFF-GRID POWER PLANTS
MICROBIAL FUEL CELLS