Controllable Synthesis of N-/S-Doped and N,S-doped hollow carbon spheres for the oxygen reduction Reaction: A universal Mono-Micelle Self-Assembly strategy

Abstract

Hollow carbon spheres have attracted widespread interest. Here we propose a one-pot universal mono-micelle self-assembly strategy that synthesises N-/S-doped or N,S-doped hollow carbon spheres from an amphiphilic diblock copolymer [polystyrene–block–poly(ethylene oxide) (PS–b–PEO)] as the structure-directing agent and heteroatom sources as the carbon precursors. The formation mechanism of the hollow structures was deduced as follows. The first step is spontaneous spherical micellisation of the hydrophobic PS block, which is mediated by strong hydrogen bond between the hydrophilic PEO block and the aqueous C2H5OH–H2O–NH3·H2O system. In the second step, spherical N-/S-doped or N,S-doped carbon precursor/PS–b–PEO micelles are formed, followed by carbonisation that converts the hydrophilic outer walls of the composites to cavity frameworks with selective removal of PS–b–PEO. The achieved N,S-doped hollow carbons (N,S-HC) exhibit superior activity and durability for the oxygen reduction reaction owing to their unique structural features, which facilitate mass transfer and an N,S dual-doped synergistic effect. This strategy can potentially synthesise novel hollow structures for diverse applications.