ORR electrocatalytic
performances of various metal atoms anchored
on hollow graphene frameworks. (a) LSV curves of N-Gr, Co-N-Gr-H,
Co-N-Gr, Fe-N-Gr, Ni-N-Gr, Cu-N-Gr, and commercial Pt/C in O2-saturated 0.1 M KOH at a scan rate of 5 mV·s–1 and 1600 rpm. (b) The corresponding Jk at 0.85 V and E1/2.
(c) LSV curves of Fe-N-Gr in O2-saturated 0.1 M KOH at
a scan rate of 5 mV·s–1 and different rotation
rates. (d) RRDE voltammograms recorded with Fe-N-Gr in O2-saturated 0.1 M KOH at 1600 rpm. (e) Peroxide yields and electron
numbers of Fe-N-Gr at various potentials based on RRDE data. (f) Chronoamperometric
curves of Fe-N-Gr and Pt/C in O2-saturated 0.1 M KOH at
1600 rpm and 0.7 V versus RHE.