For all of the advances we’ve seen with the use of hydrogen and fuel cells lately, it might be easy to wonder why we aren’t seeing fuel cell vehicles more on the roads yet despite a number of them being in trials around the world. In the last few months we’ve seen tour buses that burn hydrogen instead of gasoline in their gas-based engines, a tractor trailer sized hydrogen fuel cell mobile power plant capable of powering 600 homes, and China’s hydrogen powered light rail train appears to be up and running. Given all of this, what is the challenge around fuel cell vehicles?
The challenge, according to information from researchers at Los Alamos National Laboratory (LANL) in New Mexico: storage. While hydrogen packs a high energy content per unit mass when compared to petroleum, it also packs a low energy content per unit volume, making it hard to get enough of the element on board a vehicle to power it a reasonable distance.
So, scientists have been working with chemical compounds that store hydrogen. The star compound in these efforts: ammonia borane. Ammonia borane has a hydrogen storage capacity of almost 20%, a figure LANL says is good enough such that, with “appropriate engineering” it can be used to power a vehicle further than 300 miles. The problem is that once the hydrogen is released from the compound, there’s been no efficient way to charge it back up.
The good news is that LANL researchers, in conjunction with University of Alabama researchers, have figured out a way to “recharge” the spent fuel tanks. The process requires a sealed pressure tank and uses hydrazine and liquid ammonia at 40 degrees Celsius to recharge the tank with usable fuel, so the process has to be done at a special facility, but a tank exchange system could eliminate that inconvenience. With this method, one some day might be able to change out a fuel tank in much the same way that people exchange propane tanks for their BBQs and RVs.
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