Ambient pressure storage of high-density methane in nanoporous carbon coated with graphene

Storage and transportation of methane (CH4) remains challenging as it cannot be liquefied at ambient temperature and instead must be stored as compressed gas at high pressures (approximately 25 MPa). 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. Here we report graphene-coated porous carbon materials that can be charged with CH4 at high pressure and retain it at ambient pressure and temperature (below 318 K), thereby enhancing storage safety. 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. 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.