an external gas humidifier for fuel cell transfers recycled high - temperature waste heat produced by the fuel cell to a reactant gas , such as hydrogen or air , which is guided into the external gas humidifier . the heated reactant gas is treated in the external gas humidifier to effectively increase the moisture content of the reactant gas within a shortened time . when the humidified reactant gas enters into the fuel cell , it enables a polymeric membrane in the fuel cell to be well humidified to thereby enhance the power generation efficiency and service life of the fuel cell .