There are numerous issues to resolve on the path to the possible future widespread application of hydrogen as a vehicle fuel, but of those, the lack of an appropriate storage system currently appears not only to be a barrier, but the area that has proven the least tractable.
“Storage is idea-dependent,” said Steven Chalk, Program Manager for the DOE’s Hydrogen, Fuel Cells and Infrastructure Program, during a panel session at the NHA Hydrogen Conference. “I’m not sure that we have enough good ideas [on which] to spend [the] money.”
Although hydrogen contains nearly three times the energy content of gasoline on a weight basis (120 MJ/kg for hydrogen versus 44 MJ/kg for gasoline), on a volume basis it contains less than 25% that of gasoline (8 MJ/liter for liquid hydrogen versus 32 MJ/liter for gasoline, less for compressed hydrogen).
On-board hydrogen storage in the range of 5-13 kg H2 is needed to support the full range of types of light-duty vehicles currently in use (i.e., light compacts through beefy SUVs).
Accordingly, the DOE established a set of On-Board Hydrogen Storage Targets within the FreedomCAR program are based on, not on what current storage technologies can achieve. The baseline was current vehicles and associated customer expectations of them—e.g., a 370-mile weighted average range.
|Select FreedomCAR On-Board Hydrogen Storage Targets|
0.060 kg H2/kg
0.090 kg H2/kg
0.045 kg H2/L
0.081 kg H2/L
|Storage System Cost||$4/kWh||$2/kWh|
|Refueling Rate||1.5 kg H2/min||2.0 kg H2/min|
None of our portfolio currently meets the 2015 targets—for 2010, 700 bar [compressed] and liquid hydrogen may meet gravimetric targets, but none met the cost targets. And the volumetric targets are difficult, so there is no clear winner for 2010 targets as well.—Carole Reade, EERE Hydrogen Storage Team, at NHA Hydrogen Conference
The NHA Hydrogen Conference featured numerous presentations on developments in hydrogen storage.
BMW’s liquid hydrogen storage system for the upcoming bi-fuel 7 series. (Earlier post.)
Ovonic Hydrogen Systems described its work in developing an enhancement to its metal hydride storage system with an increase in capacity from 3 kg to 3.6 kg.
Researchers from China’s National Yunlin University of Science and Technology described their work in increasing the hydrogen storage capacity of carbon nanotubes (CNT).
Researchers from India’s University of Rajasthan and the UGC-DAE Consortium for Scientific Research presented their work on increasing the hydrogen storage behavior of intermetallic compounds.
Oregon Sustainable Energy offered up its use of Guanidine, a compound that can be synthesized from ammonia. As a side benefit, “Guanidine is also an attractive fertilizer. If produced in agricultural areas it could be used locally both as fertilizer and fuel.”
Millenium Cell described its ongoing work with sodium borohydride-based solutions.
Researchers from Argonne National Laboratory presented their work on using superactivated carbon adsorption media to enhance compressed gas storage.
Brookhaven National Laboratory is working on using titanium-doped sodium alanate for enhanced hydrogen storage.
Sodium alanate, on its own, is able to store and release a reasonable amount of hydrogen—but insufficient to meet FreedomCAR targets. Brookhaven researchers are using titanium atoms to allow sodium alanate to work more efficiently at realistic temperatures and pressures.