Theory-Guided Design and Discovery of Materials for Reversible Methane and Hydrogen Storage

One of the most persistent challenges facing our world is to shift society from fossil fuels to clean energy alternatives.1 Globally, about 36.1 billion tons of carbon dioxide are pumped into the air annually from burning fossil fuels such as oil and coal.2 Materials and technologies for reversible and high-capacity storage of gaseous fuels such as methane and hydrogen are promising alternatives to current liquid gasoline fuels due to the significantly smaller carbon footprint, as well as the exceptionally high energy density per unit mass of the former. Additionally, the United States has access to significant shale natural gas (NG) resources which makes NG a cost effective fuel.3 However, extremely high pressures or cryogenic temperatures are required to store reasonable amounts of these gaseous fuels due to low energy density per unit volume. Therefore, designing materials that can store high amounts of gaseous fuels under reasonable temperatures and pressures is a key research area for the US Department of Energy. Strategies to achieve high uptakes of methane and/or hydrogen focus on designing porous materials that can interact with methane or hydrogen on either a physical or chemical basis. For these materials to achieve suitably high capacity, rapid release, and low regeneration cost, the storage materials will need to possess high internal surface areas with optimal binding affinity to outperform current compressed 700 bar H2 or 250 bar natural gas systems on a cost and energy density basis. For automobiles or commercial trucks, a refueling pressure of 100 bar or below is preferred to remain compatible with all-metal Type I pressure tanks, circumventing the need for composite overwrapped pressure vessels (COPVs) made of costly carbon fiber-reinforced composites, where the latter could account for 55-75% of the overall COPV system cost.4-5 Additionally, the reduced compression pressure required at the fueling station will lower the cost of the process. At the same time, a minimum pressure of 5 bar remaining gas in the tank is required by the automobile industry for efficient delivery of hydrogen or methane. Practical concerns in both weight and volume of the adsorbed gas storage systems requires a fine balance between the gravimetric and volumetric capacities of sorbents for the onboard or stationary delivery of hydrogen and methane.