 "green hydrogen")
Coal may provide a potential new way to store hydrogen gas, much like batteries store energy for future use, addressing a major hurdle in developing a clean energy supply chain, according to a study.
Hydrogen is a clean burning fuel and shows promise for use in the most energy intensive sectors of the economytransportation, electricity generation and manufacturing, the researchers said.
However, much work remains to build a hydrogen infrastructure and make it an affordable and reliable energy source, they said. This includes developing a way to store hydrogen, which is currently expensive and inefficient.
"We found that coal can be this geological hydrogen battery," said Shimin Liu, associate professor of energy and mineral engineering at Penn State, US.
"You could inject and store the hydrogen energy and have it there when you need to use it," Liu said.
Geologic formations are an intriguing option, the scientists said, because they can store large amounts of hydrogen to meet the peaks and valleys as energy demand changes daily or seasonally.
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"Coal is well-studied, and we have been commercially producing gas from coal for almost a half century. We understand it. We have the infrastructure. I think coal would be the logical place to do geological hydrogen storage," Liu said.
The study, published in the journal Applied Energy, analysed eight types of coals from coalfields across the US to better understand their sorption and diffusion potential, or how much hydrogen they can hold.
Sorption is a phenomenon of capture of a gas or a vapour (sorbate) by a substance in condensed state (solid or liquid) called sorbent.
All eight coals showed considerable sorption properties, with low-volatile bituminous coal from eastern Virgina and anthracite coal from eastern Pennsylvania performing the best in tests, the researchers said.
"I think it's highly possible that coal could be the very top selection for geological storage from a scientific perspective," said Liu.
"We find that coal outperforms other formations because it can hold more, it has existing infrastructure and is widely available," he added.
Depleted coalbed methane reservoirs may be the best candidates. These contain unconventional natural gas like methane and have become an important source of fossil fuel energy over the last several decades, the researchers said. The methane sticks to the surface of the coal, in a process called adsorption, they said.
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