Review Panel Recommends “No-Go” on Further Funding for Sodium Borohydride for On-Board Vehicular Hydrogen Storage
An independent technical review panel convened at the behest of the Department of Energy to consider the technical status and progress of R&D on the hydrolysis of sodium borohydride (NaBH4) for on-board vehicular hydrogen storage has unanimously recommended a “no-go” to further funding.
Millenium Cell and others have been working on sodium borohydride-based systems for a range of applications, from portable devices to transportation. DaimlerChrysler used Millenium Cell technology it its Natrium fuel cell concept car, introduced in 2001. The Natrium (Latin for sodium, and the origin of the “Na” symbol for the element) was based on a Town and Country minivan, and used a Millenium Cell fuel processor with a Ballard fuel cell, Siemens motor and SAFT Li-ion battery pack. (Earlier post.)
When NaBH4 is suspended in an aqueous solution and then passed over a catalyst, the reaction produces hydrogen, along with a benign byproduct—sodium metaborate—that can be recycled back into sodium borohydride.
NaBH4 + 2H2O→ 4H2 + NaBO2 + heat
|Selected DOE Hydrogen Storage Technical Targets|
|System gravimetric capacity||kWh/kg
(kg H2/kg system)
|System volumetric capacity||kWh/L
(kg H2/L system)
|Storage system cost
(and H2 cost)
$/gge at pump
The panel, in its recommendation statement, said that the hydrogen storage technology considered for the hydrolysis of sodium borohydride has clearly not met all the 2007 targets. In addition, the panel saw no promising path forward for this technology to reach all the 2010 targets.
The panel reviewed materials from Argonne National Laboratory, Millenium Cell, NREL, Penn State University, Rohm and Haas, TIAX, MERIT (Material & Energy Research Institute Tokyo), the DOE Chemical Hydrogen Storage Center of Excellence, and others.
Some of the status reports provided to the panel indicated system numbers that in some cases met the 2007 targets. In particular, Millenium Cell reported on the hydrolysis of an aqueous 30% (this was not in use in the Natrium) solution of NaBH4, containing 3% sodium hydroxide (NaOH) as a stabilizer. The hydrolysis is promoted by a proprietary catalyst.
However, the panel found a number of points of concern over the practicality of the system including the unproven single-tank bladder system; the requirement for large amounts of water on board the vehicle; and issues dealing with the precipitation of the sodium borate (NaBO2) product.
Millennium Cell essentially concluded that the solution-based NaBH4 approach was not likely to achieve 2010 capacity targets. Millennium Cell also felt that the problem of accumulating a solid product was a significant engineering issue that had not been addressed adequately, and that no practical engineering solution has been proposed. Finally, Millennium Cell pointed out that the hydrogen cost remains above the target with this system.
The panel also found the high energy penalty and cost of regenerating sodium borate back to NaBH4 fuel to be of significant concern, again concluding that the 2010 hydrogen cost target did not appear within reach.
In its document, however, the review panel was careful to note that improvements in NaBH4 production have application to the cost-effective production of amine boranes, for the alternative borane-based on-board storage system, which is a major area of research under the DOE Chemical Hydrogen Storage Center of Excellence.
Therefore, the Panel is recommending that some continued research activities related to the cost-effective production of amine boranes may be appropriate. This does not contradict the Panel’s no-go recommendation for on-board sodium borohydride; the recommended future work relates to addressing the viability of chemical hydrogen storage approaches as an alternative to sodium borohydride.