Energy | 'SEARCH TERMS'

“a battery in a rock”

NATURAL GEOBATTERIES?
https://metals.co/tmc-statement-on-claims-of-dark-oxygen-production
https://newscientist.com/discovery-deep-sea-nodules-are-source-of-oxygen
Shock discovery reveals deep sea nodules are a source of oxygen
by Madeleine Cuff / 22 July 2024

“Metallic nodules scattered across the seabed in the Indian and Pacific oceans are a source of oxygen for nearby marine life – a finding that could upend our understanding of the deep ocean. Abyssal plains in some regions are scattered with potato-sized nodules packed with valuable cobalt, manganese and nickel, a target for deep-sea mining activity. Andrew Sweetman at the Scottish Association for Marine Science in Oban, UK, first noticed something strange about these ocean areas back in 2013, while conducting research in the Clarion-Clipperton Zone, a nodule-rich part of the Pacific Ocean. Sweetman and his colleagues were sending machines down to the ocean floor to seal off a 22 centimetre square patch of seabed and measure its oxygen flux. Instead of oxygen content decreasing in the monitored sections, the data suggested it was increasing. But without any noticeable plant life, that didn’t make sense, says Sweetman.

“I’ve been taught from a very young age that oxygenated ecosystems are only possible through photosynthesis,” he says. His conclusion was that the machinery he was using was faulty. “I literally ignored the data,” he says.Then, in 2021, Sweetman was on another research cruise in the Pacific and machines returned the same finding – increasing oxygen levels on the seabed. Using a different measurement approach yielded the same result. “We were seeing the same oxygen production in these two different datasets,” says Sweetman. “And suddenly I realised that for the last eight or nine years I had been ignoring this hugely groundbreaking process.”

“A nodule from the seabed being tested in a lab” Camille Bridgewater (2024)

He and his colleagues deduced that the metallic nodules must be playing a role in raising the oxygen levels in the deep sea. Lab testing, which involved poisoning the sediment and nodules, ruled out the presence of oxygen-producing microbes. Instead, Sweetman says the materials in the nodules are acting as a “geobattery”, generating an electric current that splits seawater into hydrogen and oxygen. “These nodules are being mined because there’s everything there that you need to make an electric car battery,” he says. “What if they are acting as natural geobatteries, by themselves?”

Each nodule can produce up to 1 volt of electric potential, the team discovered by probing the rocks. If the rocks were clustered together to join forces, there would be enough voltage to split seawater into hydrogen and oxygen via electrolysis, explaining the elevated oxygen levels. “Potentially we have discovered a new natural source of oxygen,” says Sweetman. “How pervasive that is in time and space, I don’t know. But it’s something that’s very, very interesting.” There are many outstanding questions. For example, the source of energy generating the electric current remains a mystery. It is also unclear whether the reaction happens continuously, under what conditions and the contribution this oxygen plays in sustaining surrounding ecosystems. “We don’t have all of the information yet, but we know it’s happening,” says Sweetman.

In deep-sea environments devoid of sunlight and plants, some life forms get their energy from chemicals that erupt from the sea floor at hydrothermal vents. Some scientists think life on Earth first appeared at these vents, but these early organisms would have needed a source of oxygen to make food from inorganic compounds. The findings raise the possibility that nodules could have been the source of that oxygen to help life get started, says Sweetman. That interpretation might be a stretch, says Donald Canfield at the University of Southern Denmark.

Oxygen is needed to produce the manganese oxide contained in the nodules, he points out. “Oxygenic photosynthesis is a prerequisite for their production,” he says. “For this reason, oxygen production by the nodules does not represent an alternative type of oxygen production to be equated with oxygenic photosynthesis. It is very unlikely that they have played a role in the oxygenation of the planet.” However, Ruth Blake at Yale University says the idea of oxygen production in the deep ocean is still “exciting” and warrants more research into the phenomenon and its potential impact on deep-ocean ecosystems.

Sweetman’s study was part-funded by The Metals Company (TMC), a deep-sea mining company looking to harvest metallic nodules in the Clarion Clipperton Zone. In response to the study, Patrick Downes at TMC said he has “serious reservations” about the findings, adding that its own analysis suggests Sweetman’s results are due to oxygen contamination from external sources. “We will be writing a rebuttal article,” Downes said in a statement to New Scientist. However, the findings are likely to strengthen calls for a ban on deep-sea mining, a position backed by many oceanographers who say our understanding of such areas is still developing.

“environmental risks of deep-sea mining”

Paul Dando at the UK’s Marine Biological Association says the paper reinforces the view of deep-sea scientists “that no mining should take place until we understand the ecology of these nodule fields”. Sweetman says his findings aren’t necessarily “the nail in the coffin” for deep-sea mining, but it might restrict extraction to locations where oxygen production is low. More research is also needed to investigate the impact of sediment stirred up by the mining process on the oxygen production, he says.”

Journal reference: Nature Geoscience DOI: 10.1038/s41561-024-01480-8

DARK OXYGEN
https://nature.com/articles/s41561-024-01480-8
https://phys.org/metallic-minerals-deep-ocean-floor
Metallic minerals on deep-ocean floor split water to generate ‘dark oxygen’
by Northwestern University / July 22, 2024

“An international team of researchers, including a Northwestern University chemist, has discovered that metallic minerals on the deep-ocean floor produce oxygen—13,000 feet below the surface. The surprising discovery challenges long-held assumptions that only photosynthetic organisms, such as plants and algae, generate Earth’s oxygen. But the new finding shows there might be another way. It appears oxygen also can be produced at the seafloor—where no light can penetrate—to support the oxygen-breathing (aerobic) sea life living in complete darkness. The study, “Evidence of dark oxygen production at the abysmal seafloor,” was published July 22 in the journal Nature Geoscience.

Deep-ocean floor produces its own oxygen
“Polymetallic nodules, collected from the ocean floor, sit in simulated seawater
in chemist Franz Geiger’s laboratory at Northwestern University”

Andrew Sweetman, of the Scottish Association for Marine Science (SAMS), made the “dark oxygen” discovery while conducting ship-based fieldwork in the Pacific Ocean. Northwestern’s Franz Geiger led the electrochemistry experiments, which potentially explain the finding. “For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” said Sweetman, who leads the Seafloor Ecology and Biogeochemistry research group at SAMS. “But we now know that there is oxygen produced in the deep sea, where there is no light. I think we, therefore, need to revisit questions like: Where could aerobic life have begun?”

Polymetallic nodules—natural mineral deposits that form on the ocean floor—sit at the heart of the discovery. A mix of various minerals, the nodules measure anywhere between tiny particles and an average potato in size. “The polymetallic nodules that produce this oxygen contain metals such as cobalt, nickel, copper, lithium and manganese—which are all critical elements used in batteries,” said Geiger, who co-authored the study. “Several large-scale mining companies now aim to extract these precious elements from the seafloor at depths of 10,000 to 20,000 feet below the surface. We need to rethink how to mine these materials, so that we do not deplete the oxygen source for deep-sea life.” Geiger is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern’s Weinberg College of Arts and Sciences and member of the International Institute for Nanotechnology and the Paula M. Trienens Institute for Energy and Sustainability.

Sweetman made the discovery while sampling the seabed of the Clarion-Clipperton Zone, a mountainous submarine ridge along the seafloor that extends nearly 4,500 miles along the north-east quadrant of the Pacific Ocean. When his team initially detected oxygen, he assumed the equipment must be broken. “When we first got this data, we thought the sensors were faulty because every study ever done in the deep sea has only seen oxygen being consumed rather than produced,” Sweetman said. “We would come home and recalibrate the sensors, but, over the course of 10 years, these strange oxygen readings kept showing up. “We decided to take a back-up method that worked differently to the optode sensors we were using. When both methods came back with the same result, we knew we were onto something ground-breaking and unthought-of.”

In summer 2023, Sweetman contacted Geiger to discuss possible explanations for the oxygen source. In his previous work, Geiger found that rust, when combined with saltwater, can generate electricity. The researchers wondered if the deep-ocean’s polymetallic nodules generated enough electricity to produce oxygen. This chemical reaction is part of a process called seawater electrolysis, which pulls electrons out of water’s oxygen atom. To investigate this hypothesis, Sweetman shipped several pounds of the polymetallic nodules, which were collected from the ocean floor, to Geiger’s laboratory at Northwestern.

“Metal nanolayers for gravitational to electrical energy conversion”

Sweetman also visited Northwestern last December, spending a week in Geiger’s lab. Just 1.5 volts—the same voltage as a typical AA battery—is enough to split seawater. Amazingly, the team recorded voltages of up to 0.95 volts on the surface of single nodules. And when multiple nodules clustered together, the voltage can be much more significant, just like when batteries are connected in a series. “It appears that we discovered a natural ‘geobattery,'” Geiger said. “These geobatteries are the basis for a possible explanation of the ocean’s dark oxygen production.”

The researchers agree that the mining industry should consider this discovery before planning deep-sea mining activities. According to Geiger, the total mass of polymetallic nodules in the Clarion-Clipperton Zone alone is enough to meet the global demand for energy for decades. But Geiger looks to mining efforts in the 1980s as a cautionary tale. “In 2016 and 2017, marine biologists visited sites that were mined in the 1980s and found not even bacteria had recovered in mined areas,” Geiger said. “In unmined regions, however, marine life flourished. Why such ‘dead zones’ persist for decades is still unknown. However, this puts a major asterisk onto strategies for sea-floor mining as ocean-floor faunal diversity in nodule-rich areas is higher than in the most diverse tropical rainforests.”

More information: Andrew Sweetman, Evidence of dark oxygen production at the abyssal seafloor, Nature Geoscience (2024). DOI: 10.1038/s41561-024-01480-8. nature.com/articles/s41561-024-01480-8

SEAWATER ELECTROLYSIS
https://pnas.org/doi/full/10.1073/pnas.1906601116
https://phys.org/news/2019-07-ultra-thin-layers-rust-electricity.html
Ultra-thin layers of rust generate electricity from flowing water
by Emily Velasco / July 30, 2019

“There are many ways to generate electricity—batteries, solar panels, wind turbines, and hydroelectric dams, to name a few examples… and now, there’s rust. New research conducted by scientists at Caltech and Northwestern University shows that thin films of rust—iron oxide—can generate electricity when saltwater flows over them. These films represent an entirely new way of generating electricity and could be used to develop new forms of sustainable power production. Interactions between metal compounds and saltwater often generate electricity, but this is usually the result of a chemical reaction in which one or more compounds are converted to new compounds. Reactions like these are what is at work inside batteries. In contrast, the phenomenon discovered by Tom Miller, Caltech professor of chemistry, and Franz Geiger, Dow Professor of Chemistry at Northwestern, does not involve chemical reactions, but rather converts the kinetic energy of flowing saltwater into electricity.

The phenomenon, the electrokinetic effect, has been observed before in thin films of graphene—sheets of carbon atoms arranged in a hexagonal lattice—and it is remarkably efficient. The effect is around 30 percent efficient at converting kinetic energy into electricity. For reference, the best solar panels are only about 20 percent efficient. “A similar effect has been seen in some other materials. You can take a drop of saltwater and drag it across graphene and see some electricity generated,” Miller says. However, it is difficult to fabricate graphene films and scale them up to usable sizes. The iron oxide films discovered by Miller and Geiger are relatively easy to produce and scalable to larger sizes, Miller says. “It’s basically just rust on iron, so it’s pretty easy to make in large areas,” Miller says. “This is a more robust implementation of the thing seen in graphene.”

Though rust will form on iron alloys on its own, the team needed to ensure it formed in a consistently thin layer. To do that, they used a process called physical vapor deposition (PVD), which turns normally solid materials, in this case iron oxide, into a vapor that condenses on a desired surface. PVD allowed them to create an iron oxide layer 10 nanometers thick, about 10 thousand times thinner than a human hair. When they took that rust-coated iron and flowed saltwater solutions of varying concentrations over it, they found that it generated several tens of millivolts and several microamps per cm-2. “For perspective, plates having an area of 10 square meters each would generate a few kilowatt-hours—enough for a standard US home,” Miller says. “Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term.”

The mechanism behind the electricity generation is complex, involving ion adsorption and desorption, but it essentially works like this: The ions present in saltwater attract electrons in the iron beneath the layer of rust. As the saltwater flows, so do those ions, and through that attractive force, they drag the electrons in the iron along with them, generating an electrical current. Miller says this effect could be useful in specific scenarios where there are moving saline solutions, like in the ocean or the human body. “For example, tidal energy, or things bobbing in the ocean, like buoys, could be used for passive electrical energy conversion,” he says. “You have saltwater flowing in your veins in periodic pulses. That could be used to generate electricity for powering implants.”

More information: Mavis D. Boamah et al. Energy conversion via metal nanolayers, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1906601116

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