Hydrogen is often regarded as a viable clean burning alternative to our current petroleum based fuel sources as a result of its high gravimetric energy density and renewable nature. Furthermore, H2 has received significant attention as a transportation fuel. A severe hurdle in the implantation of H2 as a fuel resides in the difficulty of storing it in sufficient quantities for vehicles to span the same range as those currently powered by gasoline. Porous materials can be used to increase the volumetric density of H-2 inside fuel tanks at a range of pressures and temperatures. For instance, microporous metal-organic frameworks have drawn much interest for room temperature H2 storage due to their high surface areas and tunable pore chemistry. In particular, the presence of coordinatively unsaturated metal centers can increase H2 binding enthalpy.  In an effort to systematically study H2 storage in an isostructural series of metal-organic frameworks containing exposed metal cations, we synthesized four new analogues of M2(dobpdc) (dobpdc4- = 4,4�-dioxidobiphenyl-3,3�-dicarboxylate ; M = Mn, Fe, Co, Ni).  These materials feature expanded pores as compared to the widely studied M2(dobdc) (dobdc4- = 2,5 � dioxido-1,4-benzenedicarboxylate). These new materials were studied by measuring low-pressure H-2 adsorption isotherms at 77K and high-pressure isotherms up to 300 bar at 25, 0, and -25 �C. Isosteric heats of adsorption and volumetric capacities were calculated to study how the interplay of open metal sites and pore size effects H2 capacity and binding enthalpy. In addition, powder neutron diffraction experiments were employed to identify H2 binding sites in these expanded materials.

Effects of exposed metal cations on high pressure hydrogen storage in metal-organic frameworks

248th National Meeting (2014)

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