An Assessment of Strategies for the Development of Solid-State adsorbents for Vehicular Hydrogen Storage

Nanoporous sorbents are a diverse category of solid-state materials that hold considerable promise for vehicular hydrogen storage. However, although impressive properties have been demonstrated, particularly at cryogenic temperatures, materials meeting all of the targets defined by the U.S. Department of Energy are yet to be identified. In this Perspective, we provide a contemporary overview of the major known and proposed strategies for hydrogen sorbents, with the aim of guiding both ongoing research, as well as proposals to develop new storage concepts. The discussion of each strategy includes relevant literature, strengths and weaknesses, and outstanding challenges barring their adoption. We consider Metal-Organic Frameworks (MOFs), including surface area/volume tailoring, open metal sites, and binding of multiple H2 molecules to a single site. Two related classes of open framework materials, Covalent Organic Frameworks and Porous Organic Frameworks, are discussed, as are graphene and graphene oxide and doped porous carbons. Criteria for evaluating the merits of a particular materials design strategy are introduced. A brief introduction to theoretical calculations of H2 physisorption is presented to make the reader aware of both their benefits and limitations, as these have become critical tools in the ongoing effort to discover new storage materials. Finally, considerations for the synthesis and characterization of hydrogen storage sorbents is presented.