Electrolytic air dehumidification (vapor electrolysers) based on proton-exchange membrane (PEM) is competitive to conventional dehumidifiers, but serious degradation has been found in long-running applications. This study conducted the durability test of electrolytic dehumidifier, under continuous operation for more than 250 h. Changes in current and dehumidification rate were analyzed and compared to those for fuel cells and water electrolysers. Physicochemical and electrochemical changes of the materials before and after the test were investigated. Results show that higher applied potential or higher air humidity corresponds to a larger dehumidification amount, while performance attenuates more quickly over time. When the applied potential increased from 2 V to 4 V, the degradation rate increases from 23% to 67% at 90% air humidity. Simultaneously, the internal resistance of PEM element increased from 0.419 to 1.45 Omega and the reaction resistance changed from 1.13 to 2.17 Omega, indicating by in-situ and ex-situ EIS. By characterization analysis, it indicated that the corrosion of the anode-side catalyst IrO2 is the main reason for the long-term attenuation. The grain size of almost all IrO2 faces reduced after 250 h dehumidification, and the content of active metal of the catalyst lost by 54.3%. The dissolution rate of IrO2 also increases with increasing applied potential. Besides, there is almost no physical or chemical damage on PEM or cathode catalyst before and after the durability test. This research clarifies the micro-scale changes of the materials during long-term operation, and discloses the degradation mechanism of PEM-based electrolytic dehumidifiers. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.5