Hydrogen fuel cells for automobiles the advantage of on-board hydrogen generation
By Dr. Robert Buxbaum
REB Research & Consulting, co., January 2, 2011
When considering the possible sources of hydrogen for automotive fuel cells, it is important to look for one that satisfies the reasons you had to add a hydrogen-fueled fuel cell in the first place. To this, there appear to be 4 major objectives for powering a car by fuel cells: (1) Save money - only possible if you get the hydrogen more cheaply than gasoline on a dollar-per-mile basis. (2) Save the planet - only possible if you make the hydrogen from a non-polluting source like trees or wind. (3) National security - only really applies to decision makers on the higher levels of government. (4) Some additional automobile feature: can you do something with a hydrogen- fuel cell car that you cannot with an ordinary gasoline-powered car?
Of the various ways to provide hydrogen for automotive fuel cells, only on-board hydrogen generation appears to provide all of the 4 advantages above. This is particularly apparent if the hydrogen is made from methanol water reforming. Other options can give some of the above 4 advantages, but only an on-board hydrogen generator gives you all.
Consider the first object, saving money: Hydrogen gas costs currently (January 2011) about $25/kg. As 1 kg of hydrogen in a fuel cell provides approximately the same motive energy as 1 gallon of gasoline in an internal combustion engine, we find that hydrogen gas is almost 10 times more expensive than gasoline in terms of miles per gallon. By contrast, methanol currently costs about $1.00 per gallon. Though it has about half the energy content of gasoline one can make most of that difference back by extracting the chemical energy in the form of hydrogen and combusting it in a fuel cell. Thus, on-board reforming of methanol to make hydrogen provides the sale cost per mile as gasoline costing about $1.30/gallon. That is, reformed methanol-water provides work-energy at about half the cost of gasoline. That is, on-board production of hydrogen from methanol reforming saves money -- at lest in terms of operating expenses, while use of hydrogen gas does not save the driver money at current hydrogen prices.
Now consider the second reason to use hydrogen in an automobile: saving the planet. Hydrogen is usually made from natural gas but can also be made from wood, or electrolytically from wind power or nuclear power electricity. Thus hydrogen in any form is generally thought to be good in terms of global warming and other pollution effects. Similarly, methanol is usually made from natural gas, but can also be made from wood relatively easily (it's called wood alcohol). Methanol is thus approximately equally eco-friendly as hydrogen gas, with the following disadvantage that it is not easily made from electricity. To counter this, it has a great advantage over hydrogen gas in that it is far easier to ship over highways. Methanol is a lot more energy dense than hydrogen, and a lot less flammable. Thus the cost to deliver methanol - water to an automobile is a lot less than the cost to deliver hydrogen to a similar vehicle.
The third reason to power a car using methanol- steam reforming is national security. We (Citizens of The United States) are blessed with ample resources of natural gas, water, and wood, but not as much with oil. Powering ones car with these materials helps reduce our dependence on foreign powers. Hydrogen might be an equally good option at reducing our dependency on foreign energy except that hydrogen has a much lower energy density, and thus provides fewer miles per tank-full. At this point, I should mention an equally good option for reducing the US dependence on foreign oil, direct combustion of natural gas. This option has other drawbacks, but is more- easily implemented in times of national emergency than a similar switch to any hydrogen -powered fuel cell.
Finally, the fourth issue: can you do something new and exciting with fuel cells that you can't with gasoline. Here, I'd say, the key new feature is continuous, always on, electricity to power Internet connectivity, fax machines, a refrigerator, etc. The energy density of methanol-water is about 20 times that of lithium batteries in terms of weight, and about 10 times in terms of volume (After the energy is extracted through a membrane-reactor hydrogen generator and a fuel cell. The numbers decrease to 10 and 5 respectively). There is a similar weight and volume advantage of hydrogen generated from methanol -water when compared to compressed hydrogen gas. This advantage, and the low cost of methanol-water makes it reasonable to put new electrical features into an automobile or conversion van. While a van with an always-on refrigerator will likely drain the battery in a few days, one should have weeks of run-time where the electricity is generated in a fuel cell powered by a methanol-water -fed hydrogen generator. Amenities like this can be a big advantage for campers, truckers, and even traveling salespeople.
Another automotive amenity that can be provided by hydrogen-fuel-cell electricity is always-on fax or computer, or always-available battery charging. These should appeal to road warriors, or to real-life warriors, as in the military. A soldier will tend to carry more weight in batteries than in food or ammunition; having widely available fuel-cell battery chargers would be a great advantage when combined with rechargeable batteries for mobile computers (military or not), cell phones, night vision goggles, air conditioners, gun sight systems, etc. If I were building a new car with fuel cell power, I would consider starting with small fuel cells fed by a hydrogen generator fed with methanol-water fuel. This could be aimed at road warriors, campers, and the military: people who could be expected to pay extra for these extra amenities.
Concerning hydrogen generator designs, my company makes membrane reactor based hydrogen generators. These provide several advantages for hydrogen generation for automotive fuel cells, as explained in the following article. For these customers at least, a car with a fuel cell power, produced by an on-board hydrogen generator would seem to be a real winner.