Making hydrogen

April 14, 2003
Jim Barry's letter "H2 should compete on its own" (OGJ, Mar. 3, 2003, p. 10) mentions that using hydrogen as a fuel requires "expenditure of considerable energy."

Jim Barry's letter "H2 should compete on its own" (OGJ, Mar. 3, 2003, p. 10) mentions that using hydrogen as a fuel requires "expenditure of considerable energy." For sure. But if we look deeper into this axiom, we will see the futility in trying to manufacture hydrogen on a mass scale to generate electricity with fuel cells.

From the heat of formation of water, we can calculate that the theoretical energy in electricity required to make 2 lb of hydrogen, by decomposing water is 35.1 kw-hr. The theoretical energy that a fuel cell can generate from 2 lb of hydrogen is 29.7 kw-hr. The difference is the heat of vaporization of water. The best fuel cells are 70% efficient, so they will generate only 20.8 kw-hr. The best electrolytic process is 60% efficient, so a supply of 58.5 kw-hr is required to make 2 lb of hydrogen that will, in turn, generate 20.8 kw-hr in a fuel cell. That's an input-to-output efficiency of 35.6%.

How much energy can you get from a few pounds of hydrogen? The Rocky Mountain Institute (www.rmi.org) tested its Hypercar, little bigger than a golf cart, powered by hydrogen fuel cells. It traveled 330 miles on 7.5/2 (58.5)=219 kw-hr of electricity. That's enough electricity for an average household for 3 weeks.

Turning to processes that produce hydrogen from fossil fuels, even the most efficient fuel cells cannot overcome the energy losses incurred during any process. The heats of formation of H2O, CH4, CO, and CO2 tell us the theoretical minimum energy required to produce hydrogen, and the theoretical maximum energy available by bringing hydrogen and oxygen together in a fuel cell or combustion engine.

The most cost-effective and widely used process to produce hydrogen is steam reforming of natural gas. The heats of formation of the products and reactants show that 12% of the heat value of the gas is lost during reforming. But this is for a theoretical operation where chemical reactions go to completion, and heat in the product stream is transferred perfectly without loss to the feed stream. Such conditions never occur in the real world; actual results can only be determined in a pilot plant. The theoretical case also ignores the energy demand to separate the hydrogen from CO2 and steam in the product stream. Fuel cells require pure hydrogen feed to avoid catalyst poisoning.

On the consumption side, the theoretical case assumes 100% conversion of hydrogen to electricity, whereas the best fuel cells convert only 70%. This case also ignores the energy demand to separate the greenhouse gas CO2 from the product stream, as well as the energy to transport and compress the CO2 for sequestration. Finally, the theoretical case ignores the energy to compress the product hydrogen to a sufficiently high pressure for storage. A thermodynamic calculation shows that about 20% of the energy value of hydrogen would have to be expended to compress it to 4,000 psi.

Combining all the energy losses and ancillary demands, we can see that the electrical output from hydrogen in a fuel cell will be less than if natural gas is burned directly in a turbine with 30% thermal efficiency.

We can thus conclude that the vision of hydrogen and fuel cells becoming the energy system of the future is mere illusion. Widespread production of hydrogen from any source will greatly increase industrial energy consumption. Technical advancements cannot overcome the thermodynamic hurdles that make hydrogen production and its utilization in fuel cells, a net energy loss.

OGJ readers who care to see how hard the government is promoting the hydrogen illusion can check out the many links on the website of the US Department of Energy (www.eren.doe/hydrogen).

Tom Standing
San Francisco