Table provides a comparison of liquid half-cell (thin-film rotating disc electrode; TF-RDE) performance of the electrocatalysts used in this study. For all the electrocatalysts, the electrochemically active surface area was obtained by the integration of the COelectrooxidation (ECSACO) peak, while the kinetic performance for ORR was measured at both 0.9 as well as 0.95 VRHE (specific activity; SA and mass activity; MA). The liquid half-cell TF-RDE performance was evaluated in order to confirm the eligibility of the Pt-M NIC electrocatalysts for further investigation in 50 cm 2 single-cells. This required the catalysts to exhibit a superior kinetic ORR performance in contrast to SoA Pt/C electrocatalysts as well as an ECSACO higher than at least 40 m 2 g -1 Pt 5 . According to expectations, the liquid half-cell TF-RDE kinetic performance of all Pt-M NIC catalysts at both 0.9 and 0.95 VRHE exceeds that of Pt/C from Tanaka Kikinzoku Kogyo (TEC10E50E-HT; see SI, Figure for TEM characterization and Figure for ORR polarization curve and CO-electrooxidation). In addition, the measured ORR performances are comparable or even exceed that of the d-Pt-Ni/C-JM benchmark. Lastly, evaluation of ECSACO for all Pt-M NIC electrocatalysts also confirmed the suitability for further evaluation in single-cell measurements at JM testing facilities. SA @0.9V [mA cm ] MA@0.9V [A mgPt ] SA@0.95V [mA cm ] MA@0.95V [A mgPt Prior to the single-cell evaluation, a more in-depth analysis was conducted to provide a baseline understanding of the differences between A and S-activation protocols on both the liquid half-cell TF-RDE electrochemical properties as well as in-line metal dissolution (Figure ; see also SI, Figures ). In the case of TF-RDE measurements, both A-and S-activated catalysts were first evaluated by measuring ORR (0.1 M HClO4, 1600 rpm, O2 saturated, iR corrected and background corrected, 20 mV s -1 ) followed by CO-electrooxidation (0.1 M HClO4, no rotation, Ar saturated, 20 mV s -1 ). This was then followed up by additional 50 electrochemical cycles of potential cycling activation (PCA; 0.05-1.2 VRHE, 300 mV s -1 , 0.1 M HClO4). After PCA, ORR and CO-electrooxidation were measured under the same conditions once again. and Pt-oxide formation and reduction regions can be observed (see SI, Figures and).