After being cut to the appropriate size, the anode GDE, cathode GDE, and membrane were soaked in 1.0 M KOH for 60 min (replacing the solution every 20 min) to ion exchange the quaternary ammonium groups before cell assembly. The membrane used in this work was PGT73 with 15 % cross-linking and 5 µm thickness (provided by Georgia Tech). After the KOH soak, excess KOH was removed from the membrane and GDEs, and the membrane was sandwiched between the two electrodes in 5 cm 2 active area (Scribner and Associates Fuel Cell Hardware) with single channel serpentine flow field plates. The thickness of the electrodes was measured prior to assembly to appropriately select the thicknesses of Teflon gaskets to maintain a pinch of ca. 25%. After cell assembly, N2 was flowed through the anode and cathode at 0.4 L/min at 100% relative humidity until a cell temperature of 60°C was reached. Then, the N2 feeds were switched to ultra-high purity H2 and O2 (or CO2-free air) and a constant voltage of 0.5 V was applied to initiate the cell breakin procedure. After a stable current density was established, the dew points of the anode and cathode reacting gases were systematically optimized as previously reported . The cell temperature was gradually increased to 80°C in 5°C increments, with the anode/cathode dew points being simultaneously optimized with the cell temperature to avoid membrane dry-out. After the cell equilibrated at the desired conditions for around 30 min, a polarization curve was collected by slowly sweeping the voltage from the open circuit voltage to 0.1 V at a 10 mV/s scan rate. After cell break-in and collecting of the polarization curves, steady state / durability evaluation was carried out, where the current density was held at 600 mA/cm 2 . The dew points of the anode and cathode feed were adjusted to slightly higher values than the polarization experiments to guard against membrane and cathode AEI dry out during long-term operation.