I think I understand the enthalpy based calculation of fuel cell
efficiency which yields a value of 83%. (The following link has a
concise explanation:
This calculation counts the energy input as the energy available if you
were to burn the hydrogen and the useful energy output as the input
energy minus the heat loss associated with entropy change of the
chemical reactions. This assumes that any energy not lost as
heat/entropy is available for electrical work.
I have read statements about fuel cell efficiency decreasing as more
current flows (Wikipedia) but I don't understand them. I can see that,
like for a battery, voltage and reaction rates would affect current flow
but how could that change the thermodynamics efficiency given by the
above calculation? Or is there some other measure of fuel cell
efficiency that looks at actual current flow output by the device versus
input energy?
Can anyone point me to a (readable) reference?
kyle
--
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"When applied to material things,
the term "sustainable growth" is an oxymoron."
Albert Bartlett