NOVELTY - The method for reducing degradation in a fuel cell assembly (102) including a polybenzimidazole (PBI) membrane doped with phosphoric acid, comprises electrochemically consuming oxidant from a cathode coupled to the PBI membrane in response to a disconnection of an external load, and supplying fuel to maintain zero or near zero potential by removing any back-diffused oxidant to the associated anode (108) or cathode electrode (106) of the fuel cell sufficient to consume or replace the back-diffused oxidant while the external load is disconnected.    USE - The method is useful for reducing degradation in a fuel cell assembly, which is useful in a fuel cell system (claimed).    ADVANTAGE - The method reduces or avoids conditions during standby mode that cause reduced mechanical integrity of the polybenzimidazole membrane thus increasing performance and life of the fuel cells.    DETAILED DESCRIPTION - The method for reducing degradation in a fuel cell assembly (102) including a polybenzimidazole (PBI) membrane doped with phosphoric acid, comprises electrochemically consuming oxidant from a cathode coupled to the PBI membrane in response to a disconnection of an external load, supplying fuel to maintain zero or near zero potential by removing any back-diffused oxidant to the associated anode (108) or cathode electrode (106) of the fuel cell sufficient to consume or replace the back-diffused oxidant while the external load is disconnected, reducing the fuel cell temperature below a predetermined temperature while maintaining low cell potential, where the predetermined temperature is lower than an operating temperature of the fuel cell, discontinuing an oxidant supply in response to disconnection of the external load, and maintaining the fuel cell temperature at the predetermined temperature while the external load is disconnected. The fuel is supplied at a predetermined rate without a supply of inert gas to the anode and/or cathode. The electrochemically consumed oxidant includes oxidant supplied during previous operation of the fuel cell in power delivery mode. An internal load is applied to the fuel cell to electrochemically consume the oxidant and applied during the removal of the back-diffused oxidant. The removal of the external load is determined when a detected voltage of the fuel cell is greater than or equal to a threshold value. An INDEPENDENT CLAIM is included for a fuel cell system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic illustration of a back-up power supply system including a fuel cell system and various auxiliary components of the fuel cell system.    Fuel cell assembly (102)    Electrolyte (104)    Cathode electrode (106)    Anode electrode (108)    Anode inlet. (116)