New method stores high-density methane in graphene-coated nanoporous carbon

Methane (CH₄), one of the most abundant natural gases on Earth, is still widely used to power several buildings and to fuel some types of vehicles. Despite its widespread use, storing and transporting this gas safely remains challenging, as it is highly flammable and requires compression at high pressures of around 25 megapascals (MPa).

Most existing solutions to store CH₄ at high pressures rely on expensive equipment and infrastructure, such as reinforced tanks, specialized valves and advanced safety systems. In addition, damage to this equipment or its malfunction that prompts leakage of gas can lead to explosions, fires and other serious accidents.

Some researchers have thus been trying to devise alternative strategies to store and transport CH₄ that are both safer and more cost-effective. One of these recently proposed methods, known as absorbed natural gas (ANG), entails the use of nanoporous materials, solid materials containing tiny pores in which gas molecules could be trapped at moderate pressures.

Despite their promise, many ANG approaches have been found to be unreliable, as even small increases in temperature can prompt the release of CH₄ from the materials and into the surrounding environment. This means that a part of the stored gas is easily lost, while also potentially causing fires or explosions.

Researchers at Shinshu University, Morgan Advanced Materials and other institutes recently introduced a new promising strategy to store CH₄, leveraging graphene-coated porous carbon materials. This new approach, outlined in a paper published in Nature Energy, was found to enable the safe storage of the gas at ambient temperatures and pressures, while also reducing the release of CH₄ molecules when temperatures rise.

“Storage and transportation of methane remains challenging as it cannot be liquefied at ambient temperature and instead must be stored as compressed gas at high pressures (approximately 25 MPa),” wrote Shuwen Wang, Fernando Vallejos-Burgos and their colleagues in their paper.

“Alternatively, it can be stored within nanoporous materials at moderate pressures (for example, 3.5 MPa), but this ‘adsorbed natural gas’ approach can suffer from substantial desorption with only minor temperature increases. Both methods, therefore, necessitate additional safety measures.”

The primary objective of this recent study was to overcome the limitations of existing solutions for storing CH₄, using graphene-coated and porous carbon-based materials. These materials can capture CH₄ molecules at high pressure, retaining them even at ambient pressures and temperatures below 318K.

“Our data suggest that graphene serves as a thermally controllable lock that obstructs or activates pores to trap or release CH₄, enabling a pressure-equivalent loading of 19.9 MPa at 298 K, and release upon heating to 473 K,” wrote Wang, Vallejos-Burgos and their colleagues.

“The resulting reversible CH₄ volumetric capacity reaches 142 v/v, exceeding that of various adsorbed natural gas materials at 3.5 MPa and 298 K when considering container space utilization.”

The initial findings gathered by Wang, Vallejos-Burgos and their colleagues highlight the potential of their proposed methane-storage strategy, suggesting that it could be more effective and safer than other currently used methods. After it is validated in further tests, this newly introduced strategy could be deployed in real-world settings, where it could significantly reduce the risks and difficulties associated with transporting this widely used fuel.

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