Aug 31 2011

The Coming Hydrogen Economy

Just a decade ago hydrogen fuel cells were going to change our world. We were going to have an infrastructure to distribute hydrogen and fuel cells in our cars that are so efficient and environmentally clean that you could use them to power your home.  So confident were the predictions of the “coming hydrogen economy” that car companies (like GM) banked on the technology, deciding to leap frog over hybrids. George Bush called for investment in the technology, and California’s govenator decided to get a head start on building the hydrogen infrastructure.

Now, a decade later, the hydrogen economy seems like just another false promise of future technology – like flying cars and jet packs. It turns out there were some non-trivial technical hurdles that needed to be overcome, and the assumption that they would easily or inevitably be solved was unjustified.

First, it needs to be recognized that hydrogen is not an energy or fuel source. There is negligible free hydrogen on the earth. That means that hydrogen has to be stripped from hydrocarbons or some other existing fuel, or hydrogen gas has to be made by putting the energy into it. So hydrogen is largely an energy storage system, not a source of energy.

The real killer to the hydrogen economy, however, is the storage mechanism of hydrogen. Filling a tank with hydrogen is problematic in that conventional tanks cannot hold much hydrogen. You can build tanks that can hold hydrogen under very high pressure, but then those tanks would be heavy. Further, there are significant safety issues in a car accident. Such tanks may be useful for stationary fuel cells, but not for cars.

So chemists have been searching for a form of bound hydrogen that has several desirable properties. The overall system has to be light, and has to be able to hold a high density of hydrogen (efficient in terms of both mass and volume). Further, it has to be able to both store and release hydrogen quickly, while still being stable. And it has to maintain these properties over a large range of temperatures.

Every now and then we read about a “hydrogen fuel breakthrough” that typically involves chemists coming up with a form of hydrogen that improves on one or a few of these properties. But we have not yet hit the “holy grail” of hydrogen storage for fuel – something that has all of these properties to an acceptable degree.

This is very similar to the battery situation – we keep hearing about breakthroughs in battery technology that typically represent improvement in one desirable property of batteries, but not others, or even at the expense of others. We need batteries that are simultaneously light, small, with a high capacity, and fast recharge and discharge rate, and many recharge cycles. What we hear about are batteries that may be impressive is one feature, but that are unusable in other ways – all we need is for the researchers to fix the limitations and the battery will be great. But of course, we never hear the follow up, because the limitations are not fixable (at least so far).

This post was prompted by yet another “hydrogen fuel breakthrough.” Researchers have figured out a way to make use of ammonia borane, (here is the original article) a stable solid that contains significant hydrogen. They developed a catalyst that will quickly release hydrogen from the material. They system is “air stable” and light weight.

This all sounds good. The paper primarily describes the new catalyst. The authors conclude:

This mechanistic insight may lead to the development of more efficient systems for AB dehydrogenation.

So – it sounds like a decent basic science development that might have an application in hydrogen fuel storage. But it also sounds like its a long way from developing an actual working hydrogen fuel storage system.

Still, that did not prevent the headlines from declaring yet again that we have a “Breakthrough in Hydrogen Fuel Cells.”

Don’t get me wrong – I think such advances are important, and this looks like good science. My real beef is the disconnect between the reporting of such research and the real implications. It does seem that often the researchers are partly responsible, speculating freely to the press about the potential future applications of their research. Press releases are also guilty.

But it would be nice if there were more of an effort to put such research into a realistic practical context. Maybe then we would not have so many false dawns, like the coming hydrogen economy.

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