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

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 Fe2 O3 nanoparticle-embedded mesoporous polypyrrole (PPy) monolayers grown on both sides of reduced graphene oxide (rGO) nanosheets (denoted as mPPy-Fe2 O3 @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-Fe2 O3 @rGO at 800 °C yields 2D sandwich-like mesoporous nitrogen-doped carbon/Fe3 O4 /rGO (mNC-Fe3 O4 @rGO). The mNC-Fe3 O4 @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/cm2 , 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.