MEA fabrication -The MEAs used in this work consist of five layers. Nafion 1100EW (equivalent weight in g polymer/mol H+) was used to fabricate thin-layer electrodes. The cathode catalyst layers were prepared at an ionomer/carbon weight ratio of ca. 0.9 and metal loadings of ca. 0.10 mgPt cm -2 , unless specified otherwise. The anode catalyst layer was kept constant at an ionomer/carbon weight ratio of ca. 1.5/1 and a metal loading of 0.1 mgPt cm -2 .