Coal-based hydrogen storage could support a clean energy economy.


A big chunk of coal is held by a Penn State researcher. Penn State is credited.

The search for a clean energy source that can replace fossil fuels, such as hydrogen, may lead to coal, which is an unexpected discovery. In order to overcome a significant obstacle in the development of a clean energy supply chain, a team of scientists at Penn State discovered that coal may provide a viable method of storing hydrogen gas, similar to how batteries store energy for later use.

“We discovered that coal has the potential to serve as a geological hydrogen battery,” stated Shimin Liu, a Penn State associate professor of energy and mineral engineering. “You could inject and store the hydrogen energy and have it there when you need to use it.”

As a clean-burning fuel, hydrogen has potential applications in our economy’s most energy-intensive industries, including manufacturing, transportation, and electricity production. However, the scientists noted that considerable effort needs to be done to develop a hydrogen infrastructure and turn hydrogen into a cheap and dependable energy source.

Creating a method to store hydrogen, which is now costly and ineffective, is part of this. According to the experts, geologic formations present a promising solution since they possess the capacity to store substantial amounts of hydrogen, which can be utilized to balance daily or seasonal fluctuations in energy consumption.

“Coal is well-studied, and we have been commercially producing gas from coal for almost a half century,” Liu stated. “We comprehend it. The infrastructure is here. The most sensible location for geological hydrogen storage, in my opinion, would be coal.”

In order to test this, the researchers examined eight different kinds of coal from American coalfields in order to determine how much hydrogen each type of coal could contain in terms of sorption and diffusion potential.

The researchers stated in the journal Applied Energy that all eight coals demonstrated significant sorption capabilities, with low-volatile bituminous coal from eastern Virginia and anthracite coal from eastern Pennsylvania demonstrating the greatest results in experiments.

“I think it’s highly possible that coal could be the very top selection for geological storage from a scientific perspective,” Liu added. “We find that coal outperforms other formations because it can hold more, it has existing infrastructure and is widely available across the country and near populated areas.”

Potentially the best options are depleted coalbed methane reserves. Over the past few decades, these seams—which contain unconventional natural gas like methane—have grown to be a significant source of fossil fuel energy. Adsorption is the mechanism by which the methane clings to the coal’s surface.

In a similar vein, if hydrogen were injected into coal, the gas would absorb or adhere to the coal. According to the scientists, these formations frequently contain a layer of mudstone or shale on top that functions as a seal to keep methane—in this case, hydrogen—sealed until it is needed and pumped back out.

“A lot of people define coal as a rock, but it’s really a polymer,” Liu stated. Its high carbon content and numerous tiny holes allow it to hold a significant amount of gas. In comparison to other non-carbon minerals, coal is like a sponge that can store a lot more hydrogen molecules.”

To carry out the experiments, the scientists created specialized equipment. Conventional pressurized apparatus for determining sorption would not have worked since coal has a lesser affinity with hydrogen than other sorbing gases like methane and carbon dioxide.

“We did a very novel and very challenging design,” Liu stated. “Learning how to do this right took years.” We have to carefully plan the experiment system, making mistakes depending on our prior  experience with coals and shales.”

The scientists concluded that low-volatile bituminous coal is a preferable option for gassy coal seams and that anthracite and semi-anthracite coals are good options for hydrogen storage in depleted coal seams.

Communities that rely on coal mining could benefit economically from the development of hydrogen storage, which would also contribute to the development of the country’s hydrogen infrastructure.

“In the energy transition, it’s really coal communities that have been the most impacted economically,” Liu stated. “There is undoubtedly a chance to repurpose the coal region. They already possess the knowledge, abilities, and energy engineer. I believe we should take that into consideration if we can alter their economic opportunities and construct an infrastructure.”

The scientists stated that future research will concentrate on the characteristics of coal that control the rate at which hydrogen may be pumped in and out: its dynamic diffusivity and dynamic permeability.

“I think Penn State is the right place to do all this research—we have the coal reserves, we have natural gas, we have both the engineering and economic expertise at the University,” Liu stated. “This is the logical place to do this.”

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