Propellants, one class of what are known as energetic materials, are used to launch rockets, deploy airbags, or fire high-caliber shells and bullets.
Companies commonly produce them by mixing together fuels, oxidizers, and other materials into a slurry that’s poured into a mold and cured. But Monique McClain, 29, an assistant professor of mechanical engineering at Purdue University, is developing ways to fine-tune the performance of propellants by producing them through a novel route: 3D printing.
The row-by-row manufacturing process promises to enable energetic materials with new shapes, more fine-grained layers, or different compositions.
This method could offer greater control over how sensitive the propellants are to detonating, how they burn over time, how energy dense they are, and other properties that affect thrust or trajectory. Similar techniques could also improve the performance of explosives, which are used for demolition, mining, and military bombs.
Manufacturing such materials is obviously dangerous. It requires carefully controlling the pressure, temperature, and conditions under which the process operates. It’s also tricky to push the thick, sticky, clay-like substances through the tiny nozzles of a 3D printer. Given these and other challenges, to date the method has largely been limited to materials with relatively low energy density, which means less explosive or propellant power.
But McClain has helped move the field forward in several ways. She was one of the first to apply an emerging technique that involves rapidly vibrating a 3D printer’s nozzle tips to extrude such viscous substances more quickly. That allowed her to print solid rocket propellants with higher energy density. McClain has also developed new techniques for assessing the characteristics of the resulting materials.
The US Department of Defense’s Army Research Lab and several US national labs are, or will soon begin, using or evaluating some of these techniques. She can’t comment on the potential purposes of that work. But she says the methods she’s helping to develop could provide greater control over how fast rockets accelerate or how far they travel, or extend the range of other projectiles.
Since the 1950s, satellites have monitored weather patterns, crops, and geopolitical rivals by capturing light waves as they reflect off Earth’s surface. But satellite imagery is inconsistent and blurry—impaired by cloud coverage, light conditions, and distance—and most satellites in space today capture only light in the visible spectrum and perhaps a few wavelengths in the infrared spectrum.
In 2021, Awais Ahmed’s company Pixxel launched the first demo hyperspectral satellite, able to capture orbital images in more than 150 wavelengths from the visible and infrared spectrum, into orbit for commercial and public use. Different molecules reflect light in different wavelengths called spectral signatures, and by capturing a more comprehensive set of wavelengths, says Ahmed, 25, Pixxel’s satellites can provide up to 10 times as much information about Earth’s surface as current satellites. We can learn about the internal health of crops, for example, or collect molecular information about snow caps that might reveal key insights about climate change.
Pixxel launched two more hyperspectral satellites in 2022, and the company is working on using hyperspectral data to build “a health monitoring system for the planet.” Pixxel’s current clientele includes players in agriculture and mining that use the hyperspectral data to track changes in soil and biodiversity. Ahmed plans to open-source some of Pixxel’s data and provide access to select climate research labs free of cost.
Millions of tons of aluminum end up in landfills every year. To Peter Godart, 30, that’s a waste of not only usable material, but also energy.
Like the fuels that power our world today, aluminum can release energy when it undergoes chemical reactions. Godart wants to harness the energy in waste aluminum as a cleaner alternative for heavy industry. To achieve that, he invented a chemical process that can pull apart aluminum by combining it with water. The process produces heat and hydrogen, which can both be used as energy sources.
In 2022, Godart founded a company called Found Energy to bring his invention to commercial reality. The startup plans to partner with aluminum makers, which will be able to harness energy recovered from aluminum scrap to power part of their operations.
Godart’s vision is to establish a new method of recycling aluminum and turn the metal into a sustainable fuel used across industries. One cubic meter of aluminum contains twice as much energy as the same amount of diesel. That could make the metal a candidate for powering long-distance ships or industrial processes that require lots of energy today.
Tongchao Liu, 32, has developed lithium batteries that can be recharged more times than their predecessors and cost less to build. Since battery life and cost are major obstacles to electric mobility, his work could go a long way toward ensuring broader acceptance of electric vehicles.
Improving battery cycle life—the number of times you can charge and discharge a battery before it stops working—is a major challenge. Surprisingly, researchers haven’t been able to agree on what causes batteries to eventually fail.
Liu, an assistant chemist at Argonne National Laboratory in the US, answered the question by building a new diagnostic system. The system unified multiple theories by determining that most failures in lithium batteries take place at the cathode—the electrode where current flows out of a battery—and result from physical strain as internal parts of the cathode expand and contract during each charge and discharge cycle.
Next, Liu invented a new cathode structure, using a material called a perovskite, that’s better able to withstand the strain. This innovation tripled the life of the batteries he worked on, reduced the cost to build them by about 25%, and eliminated the need to use cobalt. Widely used in existing lithium batteries, cobalt is mined primarily in the Democratic Republic of Congo and Russia, where workers are exploited and environmental costs are considerable.
Liu’s breakthrough has gained the interest of commercial businesses, which are particularly interested in reducing the use of cobalt. But his longer-term ambitions include eliminating the need for other problematic elements like nickel—and inventing entirely new battery chemistries that are immune to physical strain in the first place.
Yayuan Liu, 31, is working to create modular carbon-capture devices that don’t rely on heat. Capturing carbon dioxide trapped in the air or released during factory production is an increasingly important part of our response to climate change. But the thermochemical mechanisms used today require most commercial factories with carbon-capture facilities to maintain a large, 24/7 operation. And sometimes they still consume fossil fuel to generate the heat. Instead, Liu is developing new methods that make carbon capture more universally accessible and climate friendly by replacing the thermal mechanisms with electrochemistry reactions, so that carbon dioxide can be split and released at normal temperatures and on a much smaller scale. Her vision is that “in the future, every household has a little carbon-capture device where they could deal with their own CO2 emissions,” Liu says. She developed 20 new nitrogen-based molecules that can be used to capture carbon dioxide, some reaching near-perfect efficiency. Finding viable molecules is only the first step. To turn the molecules into practical devices soon, Liu is now venturing beyond electrochemistry, where her expertise lies, and leading an interdisciplinary research group that draws on engineering, materials science, and biology.
David Mackanic, 30, is unlocking new possibilities in electronics by building batteries that can bend and flex.
Because lithium-ion batteries, which power most consumer electronics, tend to be rigid and bulky, they greatly constrain the design and function of new products. A big part of the problem is the electrolyte, the chemical part of the battery that enables an electrical charge to pass between two terminals. Most electrolytes are made of highly combustible liquids, which means lithium-ion batteries need a weighty protective casing to avoid catching fire.
As the founder of Anthro Energy, a Silicon Valley startup, Mackanic thinks he has a better solution. His fix, which he developed as a PhD student at Stanford, is an electrolyte made from a synthetic polymer. Whereas past polymer electrolytes were either brittle or poorly conductive, his is robust enough to bend without inhibiting performance. Since the polymer is nonflammable, batteries made with it don’t need a rigid case and can more easily be built into the gadgets that they power. “You can design devices with them, rather than around them,” Mackanic says.
Anthro Energy, which Mackanic launched in 2021, is now partnering with several companies to test its batteries in a range of electronics, including wearable devices, virtual-reality headsets, and electric vehicles. In the long run, Mackanic believes, his product could lead to a 30% improvement in EV range by enabling automakers to fit more battery cells into a fixed amount of space.
Our aging grids face growing strains: Renewables generate a rising share of power but fluctuate wildly with the weather or time of day. Electric vehicles demand ever more power. And increasingly extreme heat waves, floods, and storms continually threaten to knock electricity systems offline.
Making matters even more complicated, more homes and businesses are equipped with their own solar panels, batteries, or microgrids, becoming sources of electricity as well as consumers of it.
Sivaranjani Seetharaman, 33, an assistant professor of industrial engineering at Purdue University, is developing tools to keep our grids running reliably in the face of these challenges.
Among other efforts, she has developed models to evaluate how electricity systems will respond to soaring levels of demand and extreme weather, depending on the mix of sources, storage, and other infrastructure. In one instance, she and her colleagues found that if Texas’s heavy trucking sector went electric, only 11% of the fleet would have to charge at once to risk destabilizing the regional grid.
Seetharaman has used machine learning and her models to train algorithms that can help grid operators manage these increasingly dynamic, complex systems. The software tools can forecast supply and demand, or help to determine the optimal electricity sources and ideal pathways along transmission and distribution networks at any given moment, as demand, supply, and weather conditions shift.
They can also help incorporate what are known as demand response systems, through which grid operators encourage customers to dial down their energy use during moments of peak demand or, under certain conditions, do it on their behalf.
Fully addressing the grid’s looming challenges will require adding vast amounts of clean power generation, energy storage facilities, and hardware over the next few decades. But developing better algorithms and other software tools can rapidly improve the performance of today’s grids, Seetharaman says, and ensure that we’re building more efficient, flexible, and robust ones for the future.
Confronting rising carbon emissions may be the most pressing problem we face today. Stafford Sheehan, 34, believes he’s found a way not just to reduce those emissions, but also to capture existing carbon dioxide and convert it into a useful commercial product.
As the cofounder and chief technical officer of Air Company, Sheehan has developed a process for converting carbon dioxide into new products. Much as plants use photosynthesis to turn carbon dioxide and water into sugars and oxygen, Air Company’s proprietary technology combines carbon dioxide with hydrogen gas using a catalyst. The resulting liquid contains alcohols that can be separated by distillation. Air Company is currently marketing luxury cologne and vodka made from its alcohol. The product also contains compounds called paraffins, which could be used in jet fuel. These alternative fuels could be key to decarbonizing aviation.
The International Energy Agency estimates that aviation currently produces over 2% of all energy-related carbon emissions.
There are roughly 12 kilowatt hours of energy in each kilogram of jet fuel. Right now, it takes Air Company’s process roughly twice that much energy in the form of electricity to produce a kilogram of fuel. Air Company purchases renewable-energy certificates to offset the electricity this process consumes. The company currently has a limited contract with the military and hopes to be selling jet fuel on a small scale with the next few years.
“Whatever you do in the laboratory doesn’t count. Most technologies don’t die in their initial proof of concept; they die in a scale-up,” says Stafford. “We’ve demonstrated that we can run our reactor systems on scales that are relevant to industrial chemical technologies.”
Correction: An earlier version of this article mischaracterized the process by which Air Company produces its jet fuel.
Young Suk Jo
Transportation is one of the world’s most polluting industries, accounting for roughly 15% of global greenhouse-gas emissions. Electric vehicles will make a dent in those emissions in the coming decades, but batteries can’t hold enough energy to power vehicles used in other forms of global transit, like long-range trucks and transoceanic ships.
Young Suk Jo, 34, came up with a possible solution in an unlikely chemical: ammonia. Amogy, a startup Jo cofounded in 2020, is building systems that can use ammonia, typically a component of fertilizer, as a fuel to power trucks and ships.
One of ammonia’s most attractive attributes is its energy density, meaning it can pack a lot of energy into a relatively small space. Liquid ammonia can carry about three times more energy than compressed hydrogen, a leading clean fuel today.
For Amogy, the key to using ammonia in transportation is pulling it apart. One of the core technologies in the startup’s ammonia-to-power system is a chemical reactor called a cracker. This reactor breaks ammonia down into nitrogen, which can be safely released into the atmosphere, and hydrogen. That hydrogen can then be used in a fuel cell to produce electricity. Ammonia cracking isn’t a new process, but Jo and his co-inventors developed a chemical catalyst that can help the reaction run at a lower temperature, allowing the process to be done onboard vehicles. The team also developed a reactor that can run more efficiently than the current standard, turning roughly 40% of the energy in the ammonia into electricity.