There are five exchange students in Zhao Hua’s class. Here is some information about them.

If you’ve ever spent time on a beach in the Gulf of Mexico or the Caribbean, there is a solid chance you came across a slimy mass of rotten, smelly seaweed.

The specific ocean plant during those encounters is likely sargassum (马尾藻) — while helpful for absorbing CO₂, sargassum is also unbelievably harmful. It can seriously damage both shoreline and ocean ecosystems, killing red woods, seagrass and countless ocean animals. Cleanup efforts can cost tens of thousands of dollars while disturbing both tourist and fishing industries, but the AlgaRay project is showing great promise in relieving sargassum stress. In fact, its success has even earned it a place on Time’s Best Inventions of 2023.

Off the coasts of Antigua, a roughly 9-foot-wide AlgaRay robot picks up piles of sargassum until its storage container is full, at which point the autonomous robot dives 200 meters below the surface. At this depth, the air pockets that make sargassum leaves so buoyant (有浮力的) are so pressed by the water that it simply can’t float anymore. Once let go by AlgaRay, sargassum then sinks to the ocean floor. The robot can repeat this process between four and six times every hour. And thanks to a combination of solar panels, lithium batteries (锂电池), and navigational tools, AlgaRay will eventually be able to work almost non-stop.

Of course, ocean ecosystems are complex and delicate at any depth. AlgaRay’s designers are well aware of this, and make sure they won’t increase ocean floor CO₂ recklessly. A cautious pathway and detailed monitoring have been built into their approach. Additionally, they note sargassum blooms — worsened by human activities — are already causing major issues across the world.

As the name might imply, AlgaRay is inspired by manta rays (蝠鲼), which are nearly 30 feet wide and feed on algae. In time, future generations of the robot could even match man ta rays’ huge sizes.

If we want a fair shot at transitioning to renewable energy, we’ll need one critical thing: technologies that can change electricity from wind and sun into a chemical fuel for storage and vice versa (反之亦然). Commercial devices that do this exist, but most are costly and perform only half of the expectation. Now, researchers have created small lab-scale devices that do both jobs. If larger versions work as well, they would help make it possible—or at least more affordable—to run the world on renewables.

The market for such technologies has grown along with renewables: In 2007, solar and wind provided just 0.8% of all power in the United States: in 2017, that number was 8%, according to the U. S. Energy Information Administration. But the demand for electricity often doesn’t match the supply from solar and wind. In sunny California, for example, solar panels regularly produce more power than needed in the middle of the day, but none at night, after most workers and students return home.

Some companies are beginning to install massive rows of batteries in hopes of storing extra energy and balancing the financial sheet. But batteries are costly and store only enough energy to back up the power system for a few hours at most. Another option is to store the energy by transforming it into hydrogen fuel. Devices called electrolyzers (电解器) do this by using electricity—ideally from solar and wind power—to break down water into oxygen and hydrogen gas, a carbon-free fuel. A second set of devices called fuel cells can then transform that hydrogen back to electricity to power cars, trucks, and buses, or to feed it to the power system. But commercial electrolyzers and fuel cells use different catalysts (催化剂) to speed up the two reactions, meaning a single device can t do both jobs. The researchers must conquer this.

“They did a really good job with that.” says Sossina Haile, a chemist at Northwestern University in Evanston. Still, she holds a cautious view that both her new device and the one from the O’Hayre lab are small laboratory demonstrations. For the technology to have a societal impact, researchers will need to scale up the button-size devices, a process that typically reduces performance.