Voltage Drop Causes in Fuel Cells

There are four major causes of voltage drops in fuel cells:

Activation losses: they are caused because of the low speed of the reactions that take place on the surface of the electrodes: Because the electrons have to move to and from the electrode, a portion of the generated voltage is lost to drive the chemical reaction.
Fuel crossover and internal currents: this energy loss results from the portion of the fuel that passes through the electrolyte and the electron movement through it. In an ideal case, the fuel should not have that behavior, but real cases always have that phenomenon.
Ohmic losses: this voltage drop comes from the resistance of the materials of the fuel cell to the transport of electrons.
Mass transport or concentration losses: these happen due to the change in concentration of the reactants at the surface of the electrodes.

Reference:

LARMINIE, James; DICKS, Andrew. Fuel Cell Systems Explained. 2. ed. West Sussex, England: Wiley & Sons Ltd., 2003. 418 p.

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