Question:

I read the Hydrogen feature in issue 7. I would like to have more information on what is meant by “efficiency” mentioned in the “Zoom” box.

Answer:

As described in the inset, "efficiency" is the ratio of energy output to the energy potential of the fuel. In the case of the fuel cell, experts believe that it is possible to get useable mechanical energy equal to half the energy initially contained in the fuel, i.e. 1/2, 0.5 or 50%, as indicated in the main article.