A method for controlling an amount of a liquid electrolyte in a polymer-electrolyte membrane of a fuel cell is provided. The method comprises enriching one or more of a fuel flow and an air flow with a vapor of the liquid electrolyte, the liquid electrolyte being unreplenishable via an electrochemical reaction of the fuel cell. The method further comprises delivering the vapor of the liquid electrolyte to the fuel cell including the polymer-electrolyte membrane via one or more of the gas-permeable anode and or the gas-permeable cathode. In this manner, loss of liquid electrolyte from the PEM membrane of the fuel cell can be reduced, leading to improved fuel-cell endurance.