Methods and devices for rejuvenating, supplementing, or bypassing an individual
fuel cell or a group of fuel cells, in a fuel cell stack, is disclosed. The methods
and devices provide for a mechanism for removing catalyst poisons on both the anode
portion and the cathode portion of the fuel cell and providing an improvement in
the operation of the electrolytes. A controller that controls a variable resistor
or a variable power supply in parallel with an individual fuel cell or a group
of fuel cells in a stack is utilized. Adjusting the resistive value of the variable
resistor, or the voltage level of the variable power supply, directly controls
the current in the fuel cell. In accordance with Kirchoff s Current Law, decreasing
the fuel cell voltage increases the current through the fuel cell, while the fuel
cell stack is operational, and poisons deposited on the anode and cathode electrocatalysts
are removed, thereby rejuvenating the fuel cell. Typically, the removal of cell
poisons only requires short, periodic pulsing of the fuel cell potential. Methods
and devices for determining the limiting processes within a fuel cell thus enabling
the optimization of the fuel cell stack performance to diagnose the fuel cell stack
are also disclosed.