Mesoporous nitrogen-doped carbons from PAN-based molecular bottlebrushes

Abstract

Densely grafted brushes with poly(n-butyl acrylate)-block-polyacrylonitrile (PBA-b-PAN) block copolymers (BCPs) as side chains were synthesized by atom transfer radical polymerization (ATRP) using a “grafting from” technique. Owing to the covalent linkage of the arms to the backbone and the resulting strong steric repulsion between the BCP side chains, these bottlebrushes successfully overcame the partial miscibility problem existing in most BCPs at low degrees of polymerization (DP). PBA-b-PAN bottlebrushes were then pyrolyzed to form porous nitrogen-doped carbons using a two-step thermal treatment: first forming intermolecular crosslinks between the PAN blocks, following by decomposition of the PBA to create mesopores. Carbons prepared from brushes with longer PAN blocks exhibited higher surface areas, benefiting from more complete intermolecular crosslinking. Through careful adjustment of side-chain DP, carbons with surface area as high as 420 m2/g were obtained. Small mesopores (4–7 nm) with narrow size distributions, as well as significant nitrogen content (6–9 at. %), were observed. The brush-derived, nitrogen-doped mesoporous carbon was then deposited as a thin film on a glassy carbon electrode and demonstrated good electrocatalytic activity in the oxygen reduction reaction (ORR).