External humidification has been us

External humidification has been used to enable a flexible water management for PEM fuel cell by directly controlling the relative humidity of inlet reactant gases. However, in early systems, where the objective of water management has been simply reduced to the essential idea of improving the protonic conductivity of the membrane [16], fully humidified reactant gases are normally fed to PEM fuel cell indiscriminately, hence full humidification had become the typical operating condition. In any case, external humidification must be provided by humidifier units that occupy space and consume energy [1]. Having considered the trade-off between the need to improve membrane’s conductivity and the requirement of externallyinstalled humidifiers, some researchers prefer to seek for alternative water management schemes.