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Configuration of the multi-pass reactor developed in this study. Credit: Nature Energy (2025). DOI: 10.1038/s41560-025-01925-3
Scientists from the University of Cambridge have developed a new reactor that converts natural gas (a common energy source primarily composed of methane) into two highly valuable resources: clean hydrogen fuel and carbon nanotubes, which are ultralight and much stronger than steel.
Hydrogen is a promising green fuel because it burns completely, producing only water vapor and zero carbon dioxide. However, the way we make hydrogen today typically involves using high-pressure steam to break apart gas molecules, which releases significant amounts of CO 2 as a byproduct.
To avoid this, the Cambridge team wanted to perfect a technique called methane pyrolysis, which converts methane into hydrogen and solid carbon without producing carbon dioxide. However, until now, no one has been able to perform this process efficiently enough for large-scale use because traditional reactors waste too much gas.
Aaerogel being extracted from the reactor and wound onto the roller. It then shows hydrogen gas leaving the reactor through a bubbler. Credit: Nature Energy (2025). DOI: 10.1038/s41560-025-01925-3
Multi-pass reactor
The scientists solved the problem by building a multi-pass reactor, as detailed in a paper published in the journal Nature Energy. Instead of letting the gas pass through the system only once, which results in significant waste and lost energy, the unused gas is continuously recycled. The methane keeps passing back through the hot reactor until most of it is converted into hydrogen and carbon nanotube aerogels.
By operating as a closed-loop system, the reactor minimizes the amount of material that is wasted. This approach resulted in a massive leap in performance when compared to single-pass reactors, as the researchers report in their paper: "The multi-pass reactor demonstrated an 8.7-fold improvement in carbon yield and 446-fold improvement in molar process efficiency [how efficiently the system used every gas molecule]."
Methane pyrolysis to produce hydrogen and bulk CNT materials from methane. Credit: Nature Energy (2025). DOI: 10.1038/s41560-025-01925-3
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