Considering that the CVs for the ECSA are based on themeasurement of relatively small currents (<70 mA (2.4 mA cm 2)), even Pt particles that are only slightly coated with ionomer can contribute to the ECSA measurement; the UPt values are determined only by the degree of ionic contact be- tween the Pt particles and the ionomer and thus might not be affected by the uniformity and continuity of the ionomer [7].