Hydrogen gas is a carbon-free energy source that can be burned in place of fossil fuels. But its most common production method relies on methane, a potent greenhouse gas. Other known methods are costly and resource-intensive. Now researchers have found a cleaner—and, in theory, profitable—way to make hydrogen gas from waste plastic. The process also generates graphene, an extremely valuable, ultrathin carbon material used in products such as electronics, concrete and car parts.
This method could help keep heat- trapping carbon out of the atmosphere, says James Tour, a Rice University chemistry professor and senior author of a recent study on the topic, published in Advanced Materials.
For a 2020 study, Tour and his team used a strong electric current to heat plastic to about 2,700 degrees Celsius for mere milliseconds (a method called flash Joule heating), which breaks down plastic's chemical bonds. This technique produced a type of graphene that has several atom-thin sheets of carbon lattices rather than the typical single layer. It also released a gas, but the team needed to conduct further analysis to confirm what this gas was. Now the researchers have found it was up to 94 percent pure hydrogen.
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As part of the new study, the scientists did a life-cycle assessment of the process to compare it with other ways of producing the gas in terms of its cost and emissions. They found that flash Joule heating could generate 39 to 84 percent fewer greenhouse emissions than other hydrogen-production methods. It could also help pay for itself by yielding graphene—although the multilayer version is less in demand, and it's unclear what price it might sell for, says Juan Pablo Trelles, a professor of mechanical and industrial engineering at the University of Massachusetts Lowell, who was not involved with the study.
The hydrogen-generating technique works with mixed plastic waste and could also theoretically work for other carbon-based household garbage such as cardboard and paper, Tour says. Using that hydrogen on a large scale to fuel cars, power plants, and other systems could reduce greenhouse gas emissions but would require fundamental changes to the entire energy infrastructure.
Tour says multiple companies have approached him to try to license the process. “Usually you wait years, and you try to beg somebody to take a look” at a new process or product, he says. “So this is off the charts.”
