LOS ANGELES – Researchers at the Department of Energy's Pacific Northwest National Laboratory are taking a new approach to "filling up" a fuel cell car with a nanoscale solid, hydrogen storage material. Their discovery could hasten a day when our vehicles will run on hydrogen-powered, environmentally friendly fuel cells instead of gasoline engines.
The challenge, of course, is how to store and carry hydrogen. Whatever the method, it needs to be no heavier and take up no more space than a traditional gas tank but provide enough hydrogen to power the vehicle for 300 miles before refueling.
One approach is to find a solid chemical material that can hold and then release hydrogen as needed. Recently, PNNL researchers Tom Autrey and Anna Gutowska found a way to release hydrogen from a solid compound almost 100 times faster than was previously possible.
These researchers used silica in combination with ammonia borane to accelerate the release of hydrogen from ammonia borane.
The PNNL team used a nanoscale mesoporous silica material as scaffolding for ammonia borane to achieve a high rate of hydrogen release at a lower temperature than is found at the conventional scale. A lower temperature reaction, 80 degrees Celsius (170 degrees Fahrenheit), or below, is important because additional energy is not required to maintain the reaction.
To transform the ammonia borane to a nanomaterial, scientists dissolve the solid compound in a solvent and then add the solution to the mesoporous support material.
Capillary action of the porous material pulls the ammonia borane into the pores of the support. When the solvent is removed, nanosized pores filled with ammonia borane are left. Each pore is about 6.5 nanometers in diameter.
The nanoscience approach to using ammonia borane as a storage material exceeds DOE's weight and volume storage goals for 2010. As a bonus, it also avoids the volatile chemicals produced at the bulk scale.
"We found no detectable borazine, which is harmful to fuel cells, produced by the reaction in the mesoporous materials," said Autrey.
Hydrogen storage faces a few problems. Getting hydrogen out of a storage medium is just one of them. Another problem is the stage when the hydrogen is stored. Some hydrogen storage methods either require energy be expended continuously to keep hydrogen cold or the storage mechanism is too risky for cars due to accidents and equipment failure. But there is an even earlier step problem that must be solved: How to get the hydrogen into a storage medium quickly, easily, and cheaply? These researchers think they can extend their work on this material to solve the initial storage problem as well.
Based on computational thermodynamic analysis, researchers believe the process may eventually be designed to be reversible, which would allow the storage material to be regenerated and provide a sustainable hydrogen storage compound with a longer lifetime. A patent is pending on this process for hydrogen storage.
It is hard to predict when the economy may shift to hydrogen or to batteries for transportation because it is hard to predict when bright scientists and engineers will come up with solutions to the many problems holding back various energy storage approaches.