Synthesis of uniform two-dimensional nitrogen-doped graphene films via thermal evaporation as efficient oxygen reduction catalysts

Two-dimensional (2D) nitrogen-doped graphene (NG) films have attracted considerable attention as promising metal-free electrochemical catalysts for the oxygen reduction reaction (ORR). Thermal evaporation is a versatile thin film deposition technique. However, the conventional thermal evaporation techniques present challenges in producing nitrogen-rich NG thin films because of the difficulties of a controllable manner for doping graphene with N atoms. To address this, we designed a vacuum thermal evaporation system for the large-scale preparation of 2D NG thin films. Using poly(2,5-benzimidazole) (ABPBI) as a nitrogen and carbon precursor, we deposited nitrogen-rich NG thin films with a size of 50 × 50 mm² and controllable thickness within the range of 0.5–1.5 nm. The 2D NG samples exhibited a uniform thin film structure with moderate defects. The nitrogen-rich ABPBI precursor and defects, as well as the beneficial morphology and structure, endowed the optimal catalyst (2D NG-900) with a comparable ORR activity and superior stability compared with the commercial Pt/C (20 wt%) catalyst. This paper proposes a feasible strategy for fabricating 2D NG films as effective metal-free catalysts for the ORR.