Coal is not generally thought of as a clean fuel source, but it might yet have a role to play in the push for greener energy. Researchers say that it could be a great material in which to store hydrogen gas, which is one of the most promising clean fuel sources currently being explored.
There's no doubt that hydrogen holds a lot of promise as the clean energy source of the future (even though it does bring up some potential issues). After all, when it is used as fuel, its only output is water. What remains an outstanding question about its use, though, is how to store it. Hydrogen is highly flammable and finding ways to contain it safely has proven to be quite a challenge for researchers.
We've seen efforts put forth that might lead to the containment of the gas in powders, pastes, cartridges, but at this point, hydrogen-storage solutions are still more in the realm of theory than practice. Adding to the first category is a surprising idea from researchers at Penn State who suggest using coal – yes coal – as a battery of sorts that could contain hydrogen.
It's been known that coal is good at storing methane gas as it sticks to the material through a process known as adsorption. This quality of coal, the researchers say, would translate to hydrogen as well.
To test out the theory, the research team built special pressure-producing equipment to force the hydrogen into the coal.
“We did a very novel and very challenging design,” said Shimin Liu, associate professor of energy and mineral engineering at Penn State. “It took years to figure out how to do this properly. We had to properly design an experiment system, trial and error based on our previous experience with coals and shales.”
In an analysis of eight different types of coal from across the United States, the researchers found that the material is, indeed, exceptionally good at storing hydrogen. The best of the bunch was low-volatile bituminous coal found in Virginia and anthracite coal from Pennsylvania. Coal's gas-trapping feature is based on its unique compostion.
“A lot of people define coal as a rock, but it’s really a polymer,” Liu said. “It has high carbon content with a lot of small pores that can store much more gas. So coal is like a sponge that can hold many more hydrogen molecules compared to other non-carbon materials.”
Further research will delve deeper into the idea of coal as a hydrogen container, as the researchers examine the permeability and diffusivity of the material. This will help them understand how quickly hydrogen could be pumped into and out of different kinds of coal, which in turn, could lead to efficient coal-based hydrogen "batteries." Liu also points out that the research could offer hope to communities that have been hit hard by the shift away from coal.
“In the energy transition, it’s really coal communities that have been the most impacted economically,” he said. “This is certainly an opportunity to repurpose the coal region. They already have the expertise – the energy engineer and skills. If we can build an infrastructure and change their economic opportunities – I think that’s something we should consider.”
The research has been published in the journal, Applied Energy.
Source: Penn State
