Hydrogen’s allure as a renewable and environmentally friendly transportation fuel spurred more than a decade of intensive research aimed at overcoming the challenges posed by automotive applications. But storing enough hydrogen aboard a vehicle to make the lightweight compound a practical fuel remains challenging. Standard high-pressure steel tanks are far too heavy, but carbon nanotubes may help reduce the weight, according to a study in Energy Technology (2013, DOI: 10.1002/ente.201300039). Woon-Ming Lau and Ka-Wai Wong of China Academy of Engineering Physics, Chengdu, and coworkers report that carbon nanotubes can be pressurized with 5 megapascals of hydrogen and sealed with ice crystals that function like tiny valves. Ice forms via self-assembly of water molecules that aggregate at COOH groups at the nanotube openings, the researchers explain. They note that the results show that the nanotubes can be used repeatedly to store and release hydrogen with minimal leakage by exposing the tubes to water and high-pressure hydrogen and alternately lowering and raising the temperature to form and then melt the ice.