The family of the PtM (M represents transition metals such as Co, Ni, Pd, etc.) alloys is the most promising cathode electrocatalysts for proton exchange membrane fuel cells (PEMFCs) owing to their superior oxygen reduction reaction (ORR) activity to pure Pt. However, the activity gain fades with long-term PEMFC operation, and the degradation mechanism is not yet fully understood. To truly understand the degradation mechanism of the carbon supported PtM nanoparticles (PtM/C) in the cathode of a membrane electrode assembly (MEA) upon long-term PEMFC operation, it is essential to characterize the PEMFC-cycled electrode under working conditions. Herein, we showed that operando X-ray absorption spectroscopy (XAS) characterization of PtM/C electrocatalysts cycled in a PEMFC has inherent difficulties since Pt and especially M dissolve during PEMFC operation and migrate into the membrane; the bulk XAS spectrum is an average of the signals from the electrode and the membrane. Alternatively, we developed a method that allows for in situ XAS characterization on PEMFC-cycled PtM/C electrocatalysts. We justified the method by showing that the dissolved species in the membrane were separated from the PtM/C electrocatalyst in the cathode, and the in situ XAS signals arose exclusively from the electrocatalyst. (C) The Author(s) 2018. Published by ECS.