Which method is listed for hydrogen storage in carbon nanotubes?

Which method is listed for hydrogen storage in carbon nanotubes?

• A. Stored in microscopic pores of carbon nanotubes
• B. Stored as liquid under cryogenic conditions
• C. Compressed to high pressures in metal bottles
• D. Stored as a gas at ambient pressure

Answer: (A)

Hydrogen storage in carbon nanotubes mainly happens through adsorption in the nanotubes’ porous structure. The microscopic pores and high surface area provide sites where hydrogen molecules can adhere via weak van der Waals forces, allowing storage at relatively modest temperatures and pressures. This is the storage mechanism that aligns with how carbon nanotubes are described for hydrogen storage.

The other options describe conventional methods not specific to CNTs: storing hydrogen as a cryogenic liquid requires cooling to extremely low temperatures and specialized tanks; compressing hydrogen into high-pressure metal bottles is a bulk gas storage approach; storing hydrogen as a gas at ambient pressure is impractical for meaningful storage volumes with current materials. In CNTs, the emphasis is on adsorption within the porous, high-surface-area structure, not on liquid or high-pressure gas storage.