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ORNL is currently involved in the hydrogen sorption and metal hydride research. Active research areas include the investigation of single-walled carbon nanotubes for hydrogen storage and the development of of complex hydrides, such as the borohydrides, which show the potential for use in reversible hydrogen storage. For more information on DOE Hydrogen Storage, see the Multi-Year Research, Development and Demonstration Plan.
Dave Stinton, Oak Ridge National Laboratory, 865-574-4556, stintondp@ornl.gov
The goal of this project is to control the synthesis and processing of single-walled carbon nanohorns (SWNH), a novel form of carbon, as a medium with tunable porosity of optimizing hydrogen storage. The morphology of the SWNHs including their shape, surface area, and pore size are tuned during both synthesis and post-processing for optimal hydrogen storage in accordance with theory and modeling. A high temperature, tunable pulse-width laser vaporization technique to synthesize SWNHs with variable morphology at ~20 g/hr rates has been developed at ORNL. Post-processing treatments have been developed to tailor the pore size and surface area of the SWNHs and to decorate them with metal catalyst clusters. High surface area (1,900 m2/g) SWNH materials with variable pore size and metal-decorated SWNHs have been demonstrated with metals (Pt, Pd) resulting in catalyst-assisted hydrogen storage. Hydrogen storage capability measurements have demonstrated hydrogen uptake of SWNHs at 0.2-0.8 wt% at room temperature and 1-3.5% at 77K.
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Complex Hydrides for Hydrogen Storage: Studies of the Al(BH4)3 System - Gilbert Brown
Borohydride complexes of Al, Ti, and Zr have been shown to be precursors for the chemical vapor deposition of metal borides with the evolution of H2 as a by-product. This work will focus on making the reaction reversible. Volatile or liquid hydrogen storage materials are anticipated to have some engineering advantages for scale-up such as ease of heat and mass transfer. This work has demonstrated that the thermal decomposition of Al(BH4)3 (which contains 16.8 wt.% hydrogen) at less than 200°C leads to the reversible formation of AlH(BH4)2 and diborane (B2H6).
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Preliminary results suggest that addition of transition metal catalysts to nanoporous carbons with controlled nanoscale structure and porosity results in enhanced H2 adsorption. Theoretical calculations have demonstrated that this adsorption may be significantly increased if sufficient control of the structure can be attained. To optimize the design of such nanostructure, it is essential to develop atomistic models that realistically describe isotropic nanoporous carbons and to gain fundamental understanding, at the atomic and molecular level, of hydrogen interactions within metal-doped carbons.
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Hydrogen Leak Testing of Tank Liner Materials - Barton Smith The goal of this project is to test the durability of tank liner materials used in high pressure gaseous hydrogen storage vessels using ORNL’s unique internally heated high-pressure permeation test vessel (IHPV). The IHPV allows for automatic hydrogen diffusion and permeation measurements at temperatures between -40 and 1000°C and at pressures up to 40,000 psi. This apparatus has previously been used to support the hydrogen delivery program to determine real time hydrogen permeation in low-carbon steel and polymer materials. Material characteristics such as the temperature- and pressure-dependent hydrogen solubilities, diffusion coefficients, and permeation coefficients are extracted from measurements of hydrogen flux through steel and polymers. This project will implement the SAE test protocol for durability test cycling to verify the lifecycle performance of high-pressure tank liners. This test protocol calls for thermal cycling (up to 5500 cycles) between -40 to 125°C at hydrogen pressures of 6,250 and 12,500 psi. Initial testing will survey HDPE samples provided by OEMs. Project Contact:
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The Hydrogen Storage Program element will focus on the research and development of on-board vehicular hydrogen storage systems that will allow for a vehicle driving range of more than 300 miles. System-based gravimetric, volumetric, and cost targets for hydrogen storage have been developed. Storage approaches currently being pursued are (1) on-board reversible hydrogen storage focused on materials-based technologies, with some effort on low cost and conformable tanks as well as compressed gas/cryogenic hybrid tanks, and (2) off-board regenerable hydrogen storage such as chemical hydrogen storage. Rather than emphasizing pre-commercial technology development (such as high-pressure tanks), the primary investment focus is on exploratory research as well as new materials and concepts with potential to meet long-term goals.
Basic research is essential for identifying novel materials and processes that can provide potential breakthroughs needed to attain 6 wt.% H2 for onboard vehicle storage. Metal hydrides are one class of materials that exhibit the potential to achieve this DOE Hydrogen Program goal. This project seeks to develop the chemistry for a hydrogen storage system based on complex hydrides such as the borohydrides or the alanates. ORNL is collaborating with Metal Hydride Center of Excellence partners in developing new materials and synthetic methods for producing materials as well as in studying chemical reactions. The chemistries of liquid and volatile metal borohydrides such as Al(BH4)3, Ti(BH4)3, and Zr(BH)4 are being developed. 