Hydrogen - the ever-illusive solution to our energy problems.
As a society that doesn't quite accept that you "can't take it with you," scientists have been on the hunt for portable energy storage solutions and can't look away from bright, taunting hydrogen, which stores more energy per unit of weight than any other element.
One group of researchers at the U.S. Department of Energy's Savannah River National Laboratory (SRNL) believe they may have discovered the key to portable fuel cell systems – aluminum hydride (AlH3), or alane.
While hydrogen possesses many great qualities for energy storage, it also has a few flaws. While it stores an amazing amount of energy by weight, it stores four times less energy by volume than gasoline, so the trick becomes how to get enough of it onboard to supply a meaningful amount of energy.
One approach – taken by SRNL researchers – is to use chemical hydrogen storage materials like alane that put hydrogen into a solid state for storage.
The beauty of alane is that it has a very high hydrogen capacity, storing twice as much hydrogen in equal volume to liquid hydrogen, and releases the hydrogen in optimum conditions. Work by one of the team leaders, Ragaiy Zidan, also created a two-step process that doubles the amount of hydrogen that can be extracted from alane when using the traditional one-step process.
A common issue for hydrogen storage (and most initial technologies) is cost. There is a limited supply of commercially available alane, and it carries a high cost to produce. But, necessity led to innovation for the team, and through producing alane to run their studies, the researchers developed a lower-cost process for production.
"Our process overcomes some of the handicaps of traditional methods for producing alane," Zidan said in a statement. "This novel method minimizes the use of solvents, and is able to produce pure, halide-free alane."
The SRNL team isn't just hailing the potential of alane; it's out to prove that there is true application for alane systems in small fuel cell technology. Testing a "proof-of-concept" vessel containing 22 grams of alane, the researchers determined the system could scale to meet the hydrogen release rate for a 100-watt fuel cell system. So the team upped the ante with a larger system containing 240 grams of alane that powered a 150-watt commercial fuel cell at full power for three hours. That sure sounds promising.
But, there's got to be a but – or else we would've just solved all our energy problems. One of the challenges with alane, similar to all chemical hydrogen storage materials, is that once it releases the hydrogen, it isn't able to reabsorb hydrogen again without being chemically reprocessed. This is where the idea was born to trade out fuel cells at stations, and then send them to be reprocessed and refilled before put back into use. Not exactly an elegant system, but not exactly a deal breaker either.
So what is all this work for? Unlike the overwhelming focus of hydrogen fuel cells for automotive applications, the SRNL team sees the most potential for small portable power systems. Manufacturers are looking for portable power systems that can provide a lot of power and be as light as possible. They're looking for specific energies greater than 1000 watt-hours per kilogram, which is 2-3 times the current capacity of today's lithium batteries.
As researcher Ted Motka explained: "Higher specific energy means more energy per weight. The goal is to provide sufficient energy to a system that is light enough to be carried by a soldier or used in unmanned aircraft and other applications where weight is a factor."