Carbon-Based Nanostructured Adsorbents for Hydrogen Storage

Hydrogen is viewed as a clean energy alternative that could one-day replace fossil fuels in powering vehicles. For this vision to become a reality, significant advances will be required in a wide array of hydrogen related technologies. For hydrogen storage, the U.S. Department of Energy has set a goal of achieving system gravimetric and volumetric storage densities exceeding 6 wt% and 45 kg H₂/m³, respectively, to facilitate large scale commercial deployment of hydrogen fuel on several low-demand vehicle platforms by the year 2010 [1]. A generic approach to the problem based on nanoscience considerations can offer a new perspective on this problem [2]. In this approach, one considers how suitable binding sites for hydrogen can be designed and arranged in space with sufficient density, using a light host material, to simultaneously achieve high gravimetric and volumetric performance. To minimize energy input requirements during the charge/discharge cycle, and therefore optimize system efficiency, the "suitable" binding sites should stabilize hydrogen with energies in the range of 10 - 50 kJ/mol. We will discuss theoretical and experimental results on carbon nanotubes, fullerenes, and other nanostructured adsorbent materials, and explore the role of composition, doping, and local environment in tuning hydrogen storage properties. We will also describe the research activities of the recently-established DOE Center of Excellence for CarbonBased Hydrogen Storage Materials which is focused on developing new solutions for hydrogen storage on-board vehicles. The Center is researching systems that reversibly stabilize sufficient hydrogen to meet the DOE targets, and builds on existing experimental and theoretical evidence for (i) dissociative adsorption that is weaker than typical C-H bond formation, and (ii) non-dissociative adsorption that is stronger than pure physisorption. In the first case we consider reversible hydrogen spillover, while in the second the goal is molecular adsorption via structural/chemical modifications to the physisorption potential as well as complexation of dihydrogen. The Center consists of projects at Air Products and Chemicals, Inc., California Institute of Technology, Duke University, Lawrence Livermore National Laboratory, National Institute of Standards and Technology, National Renewable Energy Laboratory, Oak Ridge National Laboratory, Pennsylvania State University, Rice University, University of Michigan, University of North Carolina (Chapel Hill), and the University of Pennsylvania. 1. http://www.eere.energy.gov/hydrogenandfuelcells/mypp/ 2. http://www.sc.doe. gov/bes/hydrogen.pdf.