Fig. 5: Oxygen reduction reaction activities of stepped Pt surfaces and proposed reaction model.
From: A kinetic descriptor for the electrolyte effect on the oxygen reduction kinetics on Pt(111)
a, Peak potential of *O on terrace (E*O(terrace)) from cyclic voltammograms of 50 mV s−1 (E*O(terrace)). b, Normalized ORR activities (to that of 0.1 M HClO4). c, Illustration of different active sites, proposed ORR scenario in acidic and alkaline media on stepped surfaces, exemplified using Pt(554). Site A has a higher generalized coordination number and lower oxygen binding energy than site B. Site A serves as the dominant reactive site in acid, in which case the ORR activity follows the thermodynamic descriptor; in alkaline media, site B serves as the dominant reactive site because of the blockage of site A by cations, and the ORR activity follows the kinetic descriptor. d, Specific activities of Pt(111) and stepped surfaces as a function of HClO4 concentration. Activities were compared at 0.93 V because 0.9 V is too close to the diffusion-limiting region for Pt(553). Step density increases in a sequence of Pt(111) < Pt(151514) < Pt(554) < Pt(553); while the changes in E*O(terrace) and ORR activity follow the opposite sequence. Error bars represent the standard deviations of at least three independent measurements.
