Patterning Graphene Surfaces with Iron‐Oxide‐Embedded Mesoporous Polypyrrole and Derived N‐Doped Carbon of Tunable Pore Size

Abstract This study develops a novel strategy, based on block copolymer self‐assembly in solution, for preparing two‐dimensional (2D) graphene‐based mesoporous nanohybrids with well‐defined large pores of tunable sizes, by employing polystyrene‐block‐poly(ethylene oxide) (PS‐ b ‐PEO) spherical micelles as the pore‐creating template. The resultant 2D nanohybrids possess a sandwich‐like structure with Fe 2 O 3 nanoparticle‐embedded mesoporous polypyrrole (PPy) monolayers grown on both sides of reduced graphene oxide (rGO) nanosheets (denoted as mPPy‐Fe 2 O 3 @rGO). Serving as supercapacitor electrode materials, the 2D ternary nanohybrids exhibit controllable capacitive performance depending on the pore size, with high capacitance (up to 1006 F/g at 1 A/g), good rate performance (750 F/g at 20 A/g) and excellent cycling stability. Furthermore, the pyrolysis of mPPy‐Fe 2 O 3 @rGO at 800 °C yields 2D sandwich‐like mesoporous nitrogen‐doped carbon/Fe 3 O 4 /rGO (mNC‐Fe 3 O 4 @rGO). The mNC‐Fe 3 O 4 @rGO nanohybrids with a mean pore size of 12 nm show excellent electrocatalytic activity as an oxygen reduction reaction (ORR) catalyst with a four‐electron transfer nature, a high half‐wave‐potential of +0.84 V and a limiting current density of 5.7 mA/cm 2 , which are well comparable with those of the best commercial Pt/C catalyst. This study takes advantage of block copolymer self‐assembly for the synthesis of 2D multifunctional mesoporous nanohybrids, and helps to understand the control of their structures and electrochemical performance.