Degradation of materials
In the graph below, the variation of voltage with current is shown for a typical PEM stack. A fuel cell always follows the imposed load.
Stack Voltage vs Stack Current – Image courtesy of Nedstack Fuel Cell Technology BV
To follow this load, adequate hydrogen and oxygen must be present. If reactants are lacking, the fuel cell consumes materials of the electrodes, such as carbon, and damages itself.
Prevention is ensured by assuring the availability of hydrogen and air must before a load is applied. Cell voltage monitoring is installed to prevent damage when the load settings are too high. A group of stacks will stop automatically when the cell voltage on any stack in that group drops below a threshold value. (From Nedstack Fuel Cell Technology BV)
Constructing fuel cells with durable materials reduces risk of degradation and increases life span. For example, PowerCell’s unit cells consist of compact and lightweight metallic bipolar plates combined with durable and highly efficient membrane electrode assemblies. (From PowerCell Sweden AB)
Overheating
The PEM fuel cell stacks manufactured by Nedstack operate at temperatures around 65ºC. Excess heat generated during power generation is transferred by a cooling medium. This is pure water with an electric conductivity below 5 µS/cm. The water needs to maintain a low conductivity to prevent short circuit currents between individual cells. The demineralized water efficiently carries the generated heat. (From Nedstack Fuel Cell Technology BV)