Abstract: A polymer electrolyte fuel cell includes fuel cell units arranged along a common axis in a stack with an inner periphery of the fuel cell units defining a fuel flow channel through which the fuel can flow in an axial direction. Current collectors are electrically connected to the fuel cell units at the top and bottom of the stack. One or more diffusion cell units are stacked below the lower current collector and have an inner periphery defining a continuation of the fuel flow channel. The fuel inlet allows the introduction of hydrogen fuel to the top end of the flow channel while the bottom end of the flow channel below the diffusion cell units is blocked. Water vapor and inert gases collecting at the bottom end of the fuel flow channel diffuse out through the diffusion cell units to maintain the electrical generating efficiency of the active fuel cell units. Diffusion cell units may be mounted in the middle of the stack where fuel is fed in from both ends of the stack.