Figure 4. Analysis of oxygen reduction on pure Co-Pi and rGO-Co-Pi.

LSV curves at various different rotation rates for (a) rGO-Co-Pi showing well-defined diffusion-controlled wave in comparison with ill-defined wave for sole Co-Pi (b). The current density for rGO-Co-Pi is obviously higher than that for Co-Pi. K-L plots on (c) G-Co-Pi and (d) pure Co-Pi layer having good linear relationship; (e) the dependence of the electron transfer number on the potential for both G-Co-Pi (black line) and sole Co-Pi layer (red line) suggesting that four-electron process also joins the ORR after hybridization with rGO; (f) Peroxide yield of G-Co-Pi (black line) and sole Co-Pi layer (red line) at various potentials in an O₂-saturated 0.1 M KOH solution (The Pt ring electrode was polarized at 0 V for oxidizing H₂O₂ intermediate). The peroxide intermediate is much more depressed in rGO-Co-Pi, indicating that rGO efficiently improves the ORR behaviors of Co-Pi electrode.