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Problems with hydrogen-fuelled cars – case: sodium borohydride as hydrogen storage

Kimmo Klemola
25.05.2006
Updated 12.03.2007

There are three mega problems with hydrogen:

  • Production (expensive, inefficient, hydrogen is manufactured from fossil fuels)

  • Storage (hydrogen is the houdini of elements)

  • Fuel cells (expensive and short life times)

Hydrogen is in fact a petrochemical (or fossil-based chemical) just like ammonia. Ammonia is a petrochemical, because it is made of nitrogen and hydrogen, and hydrogen is manufactured from natural gas. 

Some other problems associated with hydrogen-fuelled cars include:

  • It is obvious that the well to wheels efficiency is worse for FC cars than for diesel or gasoline cars.

  • Car manufacturers have mostly abandoned the idea of onsite H2 reformers (an example of chemically bonded hydride NaBH4 is given here). Hydrogen should be stored in pure form either as liquid or pressurized.

  • It takes a lot of energy to store or transfer hydrogen. Hydrogen leaks, which lessens the efficiency and is an environmental problem.

  • Urban pollution may be reduced, but overall CO2 emissions probably increase.

  • Electrolysis to hydrogen using wind power or solar power may sound like a good idea. However, electrolysis is very inefficient way producing hydrogen, and solar and wind power should be used to replace electricity from coal-fired power plants.

So, why do major auto manufacturers pursue hydrogen?

  • Public money available

  • Greenwashing 

  • Disguise. The auto manufaturers do not want tighter fuel efficiency standards. They want governments to believe that there is a technological breaktrough coming that will solve all the problems.

Different sources of hydrogen and different ways to store hydrogen have been proposed. One way is to convert hydrogen (H2) to sodium borohydride (NaBH4) and thus avoid hydrogen tanks in cars. In a car, NaBH4 is reformed to produce hydrogen.

But the production of NaBH4 requires hydrogen and methanol...

  1. Natural gas is steam-reformed to produce synthesis gas (H2+CO).

  2. Synthesis gas is a raw material for methanol (methanol is recycled in the process).

  3. Hydrogen is separated from synthesis gas.

  4. Hydrogen and methanol are used in NaBH4 production.

  5. In addition sodium metal and boric acid (their production is very energy intensive) are needed in NaBH4 production.

  6. NaBH4 is reformed to hydrogen (energy needed).

  7. Finally hydrogen gives energy in fuel cells.

You may fuel a car this way, but it does not sound very efficient. Nor does it sound very economic, because the price of NaBH4 is about US$25/kg.

One kg of NaBH4 contains 106.57 grams H2. That is equivalent to 0.388 liters gasoline.

The only way to deliver hydrogen to a vehicle that makes any sense at all is to chemically bond the hydrogen atoms to carbon atoms, forming a safe and convenient room temperature liquid.

And a liter of it contains 70% more hydrogen than a liter of liquid hydrogen at -252.8 C.

The main problem with hydrogen economy is the hydrogen properties that cannot be changed with political decisions or rhetoric or budget money.

How much FreedomFuel money Bush Administration should give to researchers to increase the liquid density of hydrogen to 700 g/L (tenfold)?

 

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