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Posted: December 21, 2006
A no-go decision for carbon nanotubes in the DOE Hydrogen Program
(Nanowerk News) The U.S. Department of Energy (DOE) Hydrogen Program has decided to discontinue (a “No-Go” decision) future applied research and development (R&D) investment in pure, undoped single walled carbon nanotubes (SWNTs) for vehicular hydrogen storage applications. This decision is based on the previously established criterion that pure, undoped SWNTs have not met; achieving 6 weight percent hydrogen storage (on a materials basis) at close to room temperature. However, there are certain areas of carbon nanotube research, such as metal-doped hybrid materials, that may warrant additional R&D investment.
DOE reviewed the current status and results of carbon nanotube research activities and evaluated data against technical criteria, basing its SWNT go/no-go decision on an analysis of:
1. The technical progress to date on the demonstrated capacity for hydrogen storage in pure, undoped carbon SWNTs and whether SWNTs have met the criterion of 6 weight percent hydrogen storage (on a materials basis) at room temperature,
2. Whether a technically viable pathway exists to meet the original criterion of 6 weight percent at room temperature using either pure, undoped SWNTs or a “hybrid” approach (e.g., metal doped nanotubes).
3. Whether hydrogen adsorption on carbon nanotubes at low temperature (77K) should be considered at this early stage of the DOE Hydrogen Storage Program (although the original criterion of 6 weight percent was at room temperature), and
4. Whether SWNTs may be used as model materials for fundamental research, theoretical simulation and an improved understanding of nanoscale hydrogen storage mechanisms and the interplay between factors such as hydrogen charge/discharge efficiency, thermodynamics/kinetics considerations, and volumetric/gravimetric capacities.
In addition to the above criteria, DOE considered the following factors in making its “Go/No-Go” decision:
– Progress towards meeting FY 2007 system targets;
– Potential pathway leading to attaining FY 2010 and 2015 system targets; and
– Progress toward consistent synthesis of high capacity (greater than 6 percent by weight) nanotube material.
The DOE Hydrogen Program initiated research at the National Renewable Energy Laboratory (NREL) to develop SWNTs as a storage medium for hydrogen in 1992. Investment in the level of research effort grew from one full-time equivalent (FTE) to at least 3 FTEs over thirteen years. Initial hydrogen capacity measurements on nanotubes were promising, but the most promising results could not be repeated. Uncertainty in the performance of carbon nanotubes as a storage material grew as other research groups initiated their own efforts on this material. Published hydrogen capacity results ranged from ca. 0 to over 6 percent hydrogen stored in/on the nanotubes on a weight basis. Importantly, the differences in measured hydrogen capacity could not be correlated with specific carbon nanotube synthesis methods or with various properties of the carbon nanotube structure. Although the number of publications and the worldwide level of effort on carbon nanotube R&D have continued to grow in the last decade and important progress has been achieved, uncertainty remains concerning hydrogen storage capacity on pure, undoped samples.
The DOE Hydrogen, Fuel Cells and Infrastructure Technologies Program (HFCIT) used input obtained through a Federal Register Notice, the open peer-reviewed literature, and technical feedback from the FreedomCAR and Fuel Partnership and DOE researchers to make a “No-Go” decision on future investment in pure, undoped SWNTs for vehicular hydrogen storage applications.