*2.11. In Situ Accelerated Stress Tests*

Gas diffusion electrodes (GDEs) were prepared by a spray technique. Sigracet 25- BC Gas Diffusion Layer (SGL), was used as a GDL, and the catalytic ink was deposited onto its surface, as reported elsewhere [47]. The same Pt loading of 0.2 mg cm−<sup>2</sup> was used for cathode and anode. The GDEs were hot-pressed, at a pressure of 20 kgcm−<sup>2</sup> for 5 min at 125 ◦C, onto Aquivion membrane to realize the Membrane-Electrode Assemblies (MEAs). The Accelerated stress tests (AST) in a H2/air 25 cm<sup>2</sup> single cell, at the Open Circuit Voltage and steady-state conditions, were carried out in the following operative conditions: 80 ◦C, 50% RH, 1.5 barabs, flow rate 1.5 and 2 times the stoichiometry for H2 and air, respectively [48]. The tests were performed by connecting the single cell with a commercial test station (Fuel Cell Technologies Inc.), and an AUTOLAB Metrohm Potentiostat/Galvanostat with a 20 A current booster to carry out the electrochemical diagnostics measurements. Linear Sweep Voltammetry (LSV) was carried out by feeding the anode and cathode with hydrogen and nitrogen, respectively, to determine the H2 crossover. A potential scan, ranging from 0 to 0.8 V with a scan rate of 4 mVs<sup>−</sup>1, was used to perform the LSV.
