Stack modeling and various experiments were performed to enhance stack performance, robustness, lifetime and to lower the degradation rates. The method to analyze and optimize the cell design of the PEMFC-Stack is based on experimentally supported modeling. For modeling the stack, CFD-calculations using Fluent{trade mark, serif} software were performed. The cell designs were subsequently experimentally investigated by polarization curves, gas utilization characterization measurements for anode and cathode as well as current density distribution measurements. With the improved cell design, the stack shows a more equal current density distribution, a significant better performance, an enhancement of the robustness and smaller degradation rates.