Galvanostatic or potentiostatic modes were operated with an electronic load (PLZ664WA, Kukusui). A CompactRIO system with NI 9211 for temperature measurement and NI 9215 for voltage measurement were used to collect analogue signals. The cells operated at a temperature of 60 °C, with heavy water as the coolant (D2O barely attenuates a neutron beam compared to H2O and can only be seen faintly in radiographs), flowing through the back of the cathode flow-field plate via Huber CC-1 heating circulation thermostats. Hydrogen and air stoichiometries were maintained at 1.5 and 3, respectively. Inlet gases were humidified using the bubbling method, regulated by mass flow controllers (Bronkhorst, up to 15 L/min for air and hydrogen, up to 2 L/min for nitrogen). A 3/2-way solenoid valve (JP Fluid Control) on the air side also facilitated wet and dry gas switching. Zero-grade gases were used with the following specifications: nitrogen (99.9% purity), air (99.9% purity) and hydrogen (99.995% purity).