The Hydrogen Economy's Dirty Secret

Is hydrogen actually clean, or just clean compared to fossil fuels? Even though it mostly produces water, there are some nasty side effects no one is talking about.


Just when you think you can praise hydrogen as a squeaky-clean replacement for fossil fuels, someone has to spoil the scene by asking pesky questions about pollution.

Today, we think of coal, oil, and gas as "dirty" energy sources because they release heat-trapping carbon dioxide when you burn them, thereby contributing to global warming. Sometimes coal also contains sulfur, which makes nasty, lake-sterilizing sulfuric acid rain. One potential solution: Hydrogen, which makes nothing but benign water vapor when burned.

I've long been a fan of hydrogen, and have blogged in favor of it here. But nothing is perfect (except, perhaps, that classic guitar solo in "Blue Sky" from the Allman Brothers' Eat A Peach), and I'm now wondering about one possible blemish on hydrogen's otherwise shiny facade.

The problem isn't exactly with hydrogen itself, but with the machines we might burn it in. In order to ignite the hydrogen in a typical eco-vehicle's internal combustion engine, you need a spark—as in spark plugs. Such sparks provide the energy needed to oxidize the H2 into H2O, but there's a lot more than hydrogen and oxygen in the atmosphere. We normally think "oxygen" when we draw a breath of air, but nitrogen makes up 78% of it.

We don't use N2 gas for anything directly; it simply visits and exits our lungs as inert filler. But combine it with oxygen in the fiery cylinder of an internal combustion engine and you get "NOx" compounds such as nitrate, which forms nitric acid in raindrops. Such nitrogen fixation happens naturally, whenever lightning sizzles a strip of air. But we're doing it on a huge scale now, in vehicles whose spark-plug explosions amount to miniature lightning strikes.

This isn't all bad. Nitrogen fixation is how nitrogen gas becomes biologically useful, and at least a third of the protein in our bodies is built around artificially fixed nitrogen atoms. To make fertilizer, for example, factories blast hydrogen and nitrogen with electricity to form ammonia, an important plant food that eventually enters our own bodies through the global food web. Without this human-driven fixation, there simply wouldn't be enough active nitrogen available to keep so many billions of people alive.

But you can also have too much of a good thing. Here in the Adirondack Mountains of upstate New York, many of our 3,000 lakes and ponds are still chronically acidified by nitrogen-rich emissions from coal-fired power plants and from the millions of cars and trucks upwind of us in the mid-continent. Ecologists also worry that our forests and lakes face nutritional imbalances from airborne nitrogen overloads.

Hydrogen certainly has its detractors. Some call it a deceptive savior because you have to burn fossil fuels in order to produce it, meaning that the electricity needed for splitting water into its hydrogen and oxygen components is likely to come from coal-fired power plants (though it can be derived from clean sources of electricity, including hydro dams, solar hydrolysis, and the geothermal power plants that Iceland is now counting on to support a hydrogen-based transportation system).

Some detractors also say that the water vapor from hydrogen combustion is itself a greenhouse gas, but they overlook the vast amounts of water that evaporate from the oceans day and night without parboiling us. Water vapor eventually condenses and falls out of the atmosphere as rain or snow rather than remaining aloft for thousands of years as CO2 does, so the climatic effects of hydrogen-car emissions should be minimal.

So here's my pesky question. I assume that hydrogen vehicles would be nowhere near as harmful as today's gasoline-guzzlers when it comes to air pollution, if only because they don't release CO2. But if we just re-tool our engines to accept hydrogen rather than fossil fuels, won't we still be polluting the air, waters, and woods with nitrogen oxides?

There are ways to reduce NOx production from hydrogen-driven vehicles, or so I'm told by experts who know a lot more about this sort of thing than I do. Catalytic converters help, for example, as do certain engine designs. But I've not yet heard much discussion of this problem in the sustainable energy community, which tends to treat hydrogen like a flawless panacea.

Back when sulfuric and nitric acids in rain (aka acid rain) was still the primary environmental issue of note, media attention helped to pass clean-air legislation that reduced acidic sulfur emissions from coal-fired power plants. Now that global warming occupies center stage, it's easy to forget that the nitric half of the old acid rain problem was left largely unsolved.

So let's remember that there's more to air pollution than CO2 alone, and take advantage of the coming energy-transition to stop acid rain as well. Then when we claim to have found some clean alternatives to carbon-based fuels, perhaps we'll be telling the truth.

Update from the author:

For those of you who are following this string of comments, please note:

1. The focus of this mostly pro-hydrogen piece is a question about NOx emissions from internal combustions engines

2. Although many hydrogen proponents support the use of technology other than internal combustion engines in a future hydrogen economy, the proposed use of such engines for hydrogen-burning is widely discussed on the web and in the technical literature, including "International Journal of Hydrogen Energy" and "Renewable Energy" (a Google search of "hydrogen internal combustion engine emissions" or similar wording yields an abundance of hits)

3. As noted in the article, the NOx emissions may indeed be reduced by converters and engine designs (hence much of the engineering research mentioned above).  But they are not totally prevented and can therefore represent a pollution problem.

4. Nitric acid pollution from internal combustion engines is an ongoing problem here in the northeast, hence my concern.

Thanks for your interest!

[Image by Flickr user Siemens PLM Software]

Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin's Press, March 2011).

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  • wilfred Recore

    Well written and excellent food for thought. The professor raises an important question regarding nitrogen emissions. it would be naive to believe that hydrogen as a viable fuel for internal combustion engines would fall victim to the hydrogen fuel cell and electrically driven vehicles; especially with the large auto companies already tooled for internal combustion engine manufacturing.  Thank you for the reality check.

  • Robert Evans

    dude, Our current cars do that already.    We don't live a perfect world.  Burning hydrogen is lot cleaner than fossil fuels.  I am tired of choking on cars passing by outside my house. 

  • Peter Parks

     The oil and battery industries spend tens of millions of dollars per year on disinformation campaigns and fake pundits/shills to discredit hydrogen because it beats their products on every metric.

    The waste product from hydrogen is potable water, the waste product from oil is cancer. (Oil is the root cause of cancer. ) It is worth anything to end Cancer so any arguement against hydrogen is offset by this fact alone. The waste product from batteries is Lithium poisoning and EMF caused cancer (The GM- EV1 was destroyed because of the EMF cancer risk).

    Hydrogen can now be efficiently made from water in your home or from sea-water and the competing interests can't control water so that want H2 stopped. Hydrogen can be made from sewage. Hydrogen can be made from any organic material. Making hydrogen from oil and natural gas is a wasteful and toxic thing. The oil industry will do anything to stop you from knowing this.

    The more batteries you add to an electric car, the less far it goes. Hydrogen carries more energy at less weight than any battery.

    Detroit has a deal with the oil companies to make money by using oil. Big oil does not  want Detroit using H2. Big Oil controls the U.S. DOE and orders them to delay hydrogen.

    For every negative you could get a shill to make-up about hydrogen, there are thousands of technical papers that disprove it. For every negative that you hear about oil and batteries there are hundreds of thousands of technical papers that prove it.

    The gulf coast will now experience a doubling of cancer rates within 10 years, essentially killing off the deep south because of the BP Oil spill.

    Hydrogen runs the sun and that seems to work pretty well.

  • Stuart Bogue

    We don't just "think" of coal,oil and gas as dirty,they are dirty. And not just because they turn into bad things when you burn them. Extraction,storage and transport are all damaging aspects of these fuel sources.

  • Andrew Krause

    NOx emissions require very high combustion chamber temperatures to form - temperatures that are rare in petrol and diesel engines, and are likely to be non-existent in hydrogen combustion engines. (Notwithstanding, as others have pointed out, hydrogen is most likely to be employed in fuel cells for electric drive vehicles.) 

    The only flaw in hydrogen is that it is not energy dense enough to be an economically viable carrier of energy. Technology is quickly making up the gap there.

    Here's the fly in the ointment - water vapor is the most virulent green house gas, contributing up to 72% over the overall effect. So if we're going to have this discussion, it should be on true-zero emission, eg capturing the water byproduct of a hydrogen vehicle and returning it to a recycling point - likely the same place you're getting your H2. 

  • Robert

    Water... As mentioned by the author, literally rains out of the air... (ever heard of rain?), yes, the oceans evaporate orders of magnitude more than humanity could ever release, right?
    Now, I believe that hydrogen is already becoming obsolete to advanced batteries, however, we will need it to fix nitrogen for fertilizer, eventually as natural gas becomes depleted (and it's co2 is levied). I'm hopeful that can be done with clean energy such as LFTR or even large scale solar.

  • Tom Collins

    Wow, way to go commenters! Thanks for calling it - I think you deserve a response, or both the article and the "expert" should be tossed from this mag which I hold in high regard.

  • Peter Gluck

    Burning hydrogen is  not a viable solution indeed. Randell Mill's hydrino technology ( gives 200 times more energy per a mol of hydrogen than
    obtained by burning. The very promising Ni-H Low Energy Nuclear Reaction(s) are even more efficient.
    Discovered and developed by Francesco Piantelli- now on the way to industrialization- at the
    Greek company Defkalion Green Industries- please search for Rossi "E-cat."  Burning is primitive.
    My blog, http://egooutpeters.blogspot.c... is dedicated  inter alia, to NEW ENERGY

  • Mike Mills

    I agree with all the comments.  To pile on, I'd like to point out that the photo in the article is a picture of the GM Equinox FUEL CELL hybrid electric vehicle, i.e. no hydrogen is combusted, its electrochemically converted to electricity which powers the motor, like most of the hydrogen will be used if/when it becomes a significant vehicle fuel.

  • Barrie Bain

    A little knowledge is indeed a dangerous thing.  I can't believe a science journalist with  a PhD would write such a badly researched article.  A few points:
    Where does he think the hydrogen comes from?  - it will either have to come from hydrocarbons or the electricity intensive hydrolysis of water.  Hydrogen is a secondary energy source, not a primary one like oil, gas and coal.  If you extract hydrogen from hydrocarbons, you produce CO2.
    Ammonia is not made by "blasting nitrogen and hydrogen with electricity" it is made by combining hydrogen from a hydrocarbon (most usually natural gas) with nitrogen from the atmosphere under high pressures and temperatures over a catalyst.
    NOx's are released from combustion of hydrocarbons in vehicles, power stations etc.  It can be controlled by selective catalytical reduction using ammonia or urea.  New trucks in the US from 2010 ( and in the EU for several years) have SCR systems that remove most of the NOx. Power stations are retrofitting with NOx SCR control systems.  NOx emissions are falling.
    There are a number of ways of reducing NOx from hydgen powere engines - lean burn SCR etc, but as one of the other comments said, you are more likely to use hydrogen in a fuel cell then burn it in a IC engine for a vehicle.

  • Dave

    This article is extremely misguided. Hydrogen as a source of fuel is not a replacement for fossil fuels directly. Burning hydrogen in an internal combustion engine is extremely inefficient compared to other fuels. That is why hydrogen, as a next generation fuel, is NOT a replacement for fossil fuels, it is one piece in a complete replacement of the internal combustion engine. Future hydrogen powered cars will use electric motors as the drive mechanism. They will use hydrogen to generate electricity for that electric motor.

    This author seems intent on scaring people or just belittling the technology. He is not an expert. He is either an idiot, or yet another purported 'expert' that is really just on the payroll of big oil.

  • Schmauli

    I totally agree with Dave here. This article makes no sense whatsoever. Please Fast Company, withdraw this article. It undermines the value of every other article on your site, as it does with the title 'Expert Blogger'.

    Typical eco-vehicles use fuel cells with membranes and stuff, not internal combustion engines with spark plugs.

  • jeff fountain

    Notwithstanding, hydrogen is dangerous. The most compelling argument in regards to hydrogen use for energy is safety. The technology isn't enough there to include 95% of potential human errors...and no, I'm not a big oil shrill, and neither is Stager.