Green hydrogen is touted as a promising alternative to fossil fuels, but the methods used to produce it generate too much carbon dioxide or are extremely expensive. There is light at the end of the tunnel, though.
1. Hydrogen gas and graphene
Researchers at Rice University, Texas, have found a way to harvest hydrogen from plastic waste using a low-emissions method and say “it could more than pay for itself.” The scientists exposed plastic waste samples to rapid flash Joule heating for about four seconds, bringing their temperature up to 3,100 degrees Kelvin (2,826.85 degrees Celsius), they explained in a university statement published on September 14. The process vaporizes the hydrogen present in plastics, leaving behind graphene — an extremely light, durable material made up of a single layer of carbon atoms.
“In this work, we converted waste plastics — including mixed waste plastics that don’t have to be sorted by type or washed — into high-yield hydrogen gas and high-value graphene,” said Kevin Wyss, a Rice doctoral alumnus and lead author on a study published in Advanced Materials.
If the produced graphene is sold at only 5% of current market value — a 95% off sale! — clean hydrogen could be produced for free.Kevin Wyss, lead author of the study
2. Hydrogen production
Producing green hydrogen — which is hydrogen made using renewable energy sources like wind, solar, or hydropower — is currently more expensive compared to hydrogen produced through traditional methods like steam methane reforming or natural gas reforming.
Today, green hydrogen costs roughly $5 for just over two pounds (nearly one kilo). Though cheaper, most of the nearly 100 million tons of hydrogen used globally in 2022 was derived from fossil fuels, and its production generated roughly 12 tons of carbon dioxide per ton of hydrogen.
Green hydrogen uses green power to produce hydrogen through electrolysis and this route accounts for roughly 1% of current global hydrogen production, according to Sustainability Analyst Lize Wan. The rest is predominantly grey hydrogen that is produced from methane or coal through natural gas reformation or coal gasification.
“The main form of hydrogen used today is grey hydrogen, which is produced through steam-methane reforming, a method that generates a lot of carbon dioxide,” said James Tour, Rice’s T.T. and W. F. Chao Professor of Chemistry and a professor of materials science and nanoengineering. “Demand for hydrogen will likely skyrocket over the next few decades, so we can’t keep making it the same way we have up until now if we’re serious about reaching net zero emissions by 2050.”
3. Government support
Green hydrogen is about 6-8 times more expensive than the standard energy options. To bridge the cost gap the European Union has committed to spending $350 billion on adopting green hydrogen by 2030. The US followed offering a $3/kg subsidy for the green hydrogen produced through its Inflation Reduction Act.
“When we first discovered flash Joule heating and applied it to upcycle waste plastic into graphene, we observed a lot of volatile gases being produced and shooting out of the reactor,” Wyss said. “We wondered what they were, suspecting a mix of small hydrocarbons and hydrogen, but lacked the instrumentation to study their exact composition.”
Thanks to funding from the US Army Corps of Engineers, the Tour lab acquired the necessary equipment to characterize the vaporized contents. They discovered that polyethylene is made of 86% carbon and 14% hydrogen, and they managed to demonstrate that it’s possible to recover up to 68% of that atomic hydrogen as gas with a 94% purity.
“I am glad that techniques I learned and used in this work ⎯ specifically life-cycle assessment and gas chromatography ⎯ can be applied to other projects in our group. I hope that this work will allow for the production of clean hydrogen from waste plastics, possibly solving major environmental problems like plastic pollution and the greenhouse gas-intensive production of hydrogen by steam-methane reforming,” said Wyss.
The research was supported by the US Army Engineer Research and Development Center, the Air Force Office of Scientific Research, the National Science Foundation and the Office of Naval Research.