Pyridinic N doped graphene: synthesis, electronic structure, and electrocatalytic property

TLDR

Nitrogen‑doped carbon materials display distinct electronic properties depending on the C–N bonding configuration, and single‑type C–N doping is a useful platform for studying these effects; pyridinic N has long been considered a key promoter of oxygen‑reduction activity. The study aims to synthesize single‑layer graphene doped exclusively with pyridinic nitrogen via thermal CVD of hydrogen and ethylene on Cu foils in ammonia. The authors performed thermal CVD of hydrogen and ethylene on Cu foils, adjusting ammonia flow to tune the N/C atomic ratio from 0 to 16 %. Raman, TOF‑SIMS, and UV‑photoemission spectroscopy reveal domain‑like pyridinic N that raises π‑state density near the Fermi level and lowers the work function, yet rotating‑disk‑electrode measurements show it does not effectively promote the 2e‑reduction oxygen‑reduction reaction.

Abstract

Different C–N bonding configurations in nitrogen (N) doped carbon materials have different electronic structures. Carbon materials doped with only one kind of C–N bonding configuration are an excellent platform for studying doping effects on the electronic structure and physical/chemical properties. Here we report synthesis of single layer graphene doped with pure pyridinic N by thermal chemical vapour deposition of hydrogen and ethylene on Cu foils in the presence of ammonia. By adjusting the flow rate of ammonia, the atomic ratio of N and C can be modulated from 0 to 16%. The domain like distribution of N incorporated in graphene was revealed by the imaging of Raman spectroscopy and time-of-flight secondary ion mass spectrometry. The ultraviolet photoemission spectroscopy investigation demonstrated that the pyridinic N efficiently changed the valence band structure of graphene, including the raising of density of π states near the Fermi level and the reduction of work function. Such pyridinic N doping in carbon materials was generally considered to be responsible for their oxygen reduction reaction (ORR) activity. The 2e reduction mechanism of ORR on our CNxgraphene revealed by rotating disk electrode voltammetry indicated that the pyridinic N may not be an effective promoter for ORR activity of carbon materials as previously expected.