A new way to make hydrogen from waste plastic also produces graphene as a byproduct. If the graphene is sold at its current market price, it could actually become profitable to generate hydrogen as a clean fuel.
The most common way to produce hydrogen involves reacting steam with methane sourced from natural gas. However, this process releases large quantities of carbon dioxide. There are carbon-free ways to make hydrogen, but they require large amounts of electricity and can be expensive in countries with high energy costs.
Now, at Rice University in Houston, Texas, and his colleagues have found a low-cost way to produce hydrogen without releasing CO2 by rapidly heating household waste plastics.
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As well as producing hydrogen, the process makes high-quality, commercially viable graphene. Tour and his team calculated that selling it at even 5 per cent of its current market value would mean the hydrogen costs nothing to produce. 鈥淓ven at that price, we鈥檙e making like $4.30 per kilo on hydrogen, so now hydrogen becomes free,鈥� says Tour. 鈥淵our fuel is free while you鈥檙e cleaning up the world.鈥�
The process works by repeatedly passing electricity through a sample of waste plastics mixed with a conductive material, heating them to around 2800掳C in about 4 seconds. The researchers used waste polyethylene, which makes up around 34 per cent of all plastics and is the most common plastic in the world, as their test material.
The rapid heating causes the polyethylene鈥檚 carbon atoms to bind into graphene. The process also gives off a mixture of gases: 92 per cent pure hydrogen, and the remaining 8 per cent a variety of carbon-based compounds like methane and propane.
While these byproducts could be sold on their own, Tour and his team found that hotter and faster heating produced more graphene and hydrogen with fewer residual compounds.
Once locked into graphene, the carbon is very unlikely to enter the Earth鈥檚 atmosphere as CO2 again, says Tour. 鈥淲e know that because we have graphite in the world. If microbes could eat graphite or graphene, which is single sheets of graphite, we wouldn鈥檛 have any graphite in the world. But we have graphite mines 鈥� it doesn鈥檛 decompose rapidly.鈥�
Tour鈥檚 team has only shown that the method is viable in the lab so far. But a separate company co-founded by Tour called has used the same heating method to produce graphene commercially. 鈥淵ou could have a smaller-scale deployment for generating hydrogen certainly within five years,鈥� says Tour. 鈥淵ou could have a large-scale deployment within 10.鈥�
Producing hydrogen this way could form a part of a future circular economy, says at Cranfield University in the UK. But scientists will need to solve some technical challenges before it can be deployed on an industrial scale, he says. 鈥淲e don鈥檛 know, beyond the lab scale, what kind of challenges they will encounter when they handle a massive scale of plastics, gas mixtures and byproducts, like graphene,鈥� he says.
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