Metal Doping to Control Gate Opening and Increase Methane Working Capacity in Isostructural Flexible Diamondoid...

Adsorbed natural gas (ANG) systems involve using porous materials to increase the working capacity and/or reduce the storage pressure compared to compressed natural gas (CNG). Flexible metal-organic materials (FMOMs) are particularly interesting in this context since their stepped isotherms can afford increased working capacity if the adsorption/desorption steps occur within the proper pressure range. We report herein that metal doping in a family of isostructural FMOMs, ML₂ (M=Co, Ni or Ni_x Co_1-x , L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), enables control over the gate opening between non-porous (closed) and porous (open) phases at pressures relevant to methane storage. Specifically, methane-induced phase transformations can be fine-tuned by using different Ni/Co ratios to enhance methane working capacity. The optimal working capacity from 5 to 35 bar at 298 K (153 cm³  cm^-3 ) was found for Ni_0.89 Co_0.11 L₂ (X-dia-1-Ni_0.89 Co_0.11 ), which is greater than that of benchmark rigid MOFs.