Method and control device for operating a fuel cell or a fuel cell stack

A method for operating a fuel cell or a fuel cell stack (1) is presented, which, given a constant fuel gas flow, has an electrical maximum power that can be delivered depending on the operating temperature, as well as aging that depends on the operating duration, which causes the electrical internal resistance to increase with progressing operating duration. In the method, the initial value (T0) of the operating temperature for a new fuel cell or for a new fuel cell stack is typically less than or equal to the operating temperature at which the electrical maximum power is achieved, and the fuel cell or the fuel cell stack (1) are regulated such that the decrease in the delivered electrical power as a result of aging is partially or completely compensated by increasing the operating temperature (T) of the fuel cell or of the fuel cell stack with progressing aging.