Hydrogen at Room Temperature
Materials exhibiting reversible hydrogen adsorption with high gravimetric and volumetric capacities are sought for use in on-board storage systems of hydrogen fuel cell-powered vehicles. Microporous metal-organic frameworks with high internal surface areas have been shown to display excellent storage properties, but only at cryogenic temperatures. Professor Jeffrey Long at UC Berkeley is developing methods for synthesizing frameworks containing coordinatively-unsaturated metal centers as a means of increasing the H2 adsorption enthalpy. In particular, he seeks to synthesize thermally-robust, high-surface area materials with a high concentration of open metal coordination sites. By adjusting the electronic structure of the metal ions, it is expected that an optimal H2 binding enthalpy of 15 kJ/mol can be achieved, leading to a high H2 storage capacity at room temperature and safe pressures of up to 100 bar. This approach involves the insertion and activation of metal carbonyl units on the aromatic components of existing frameworks, as well as the design of new frameworks using bridging ligands that facilitate the generation of open metal coordination sites. Related efforts to store hydrogen via a spillover mechanism, wherein metal clusters embedded within a framework can purportedly convert H2 to surface-stabilized H atoms, are also underway.
Next Steps: Professor Long and his collegues are currently testing various metals to find one with the most desirable binding energy.