The diagram shows the characteristic curve of the stack voltage UStack, the power curve of the system PSystem and the power curve of the stack PStack as a function of the stack current IStack. A vertical bar indicates the present load point of the fuel cell. The slider at the very bottom left can be used to vary the supplied hydrogen mass flow and thus the load point of the fuel cell. The diagram shows that, with increasing current, the voltage is decreasing while the power is increasing. The power of the system PSystem corresponds to the effective usable power, which is available for an external load.
The diagram shows the efficiency curves of the fuel cell system and the fuel cell stack, including the present load point, in function of the stack current. The system efficiency is lower than the stack efficiency because the system needs power for its internal electrical consumption, which is required for the operation of the system components.
The animation illustrates a detailed view of a single cell from a fuel cell stack schematically. The electrolyte of a Polymer-Electrolyte-Membrane (PEM) fuel cell consists of a polymer membrane that isolates the anode and cathode electrically. This means the membrane is permeable for protons but impermeable for electrons. Hydrogen is fed at the anodic side and oxygen is added at the cathode. With the aid of a platinum catalyst, hydrogen is oxidised resulting in the electrons being separated. The potential difference between the electrodes generates direct current.
Depending on the load point, the (stoichiometric) process of the fuel cell reaction is animated in the cell. The present values of current and voltage are displayed next to the fuel cell stack. In addition, the "consumed" electrical power at the load (light bulb) and the resulting heat flow of the fuel cell stack are shown schematically.