Figure 4: Oxygen reduction reaction on Ru/C heat-treated (HT) catalyst in 0.1 M NaOH and 0.1 M HClO4 electrolytes. (a) ORR polarization curves at 900 rpm and 20 mV/s, (b) mass-transport-corrected Tafel plots, (c) ring current measured during ORR at 900 rpm. = 1.1 V versus RHE in 0.1 M NaOH and  V versus RHE in 0.1 M HClO4, and (d) hydrogen peroxide reduction reaction (HPRR) in comparison to ORR in 0.1 M HClO4 and 0.1 M NaOH. HPRR is shown in oxygen-free electrolytes containing externally added H2O2 at a concentration of 3.5 mM.