We report a F-doped FeNC catalyst with improved ORR performance. The enhanced performance is associated with the large BET surface area, abundant single Fe atoms, and strong electron-withdrawing F-doping.

Iron atoms coordinated with nitrogen (FeN x ) sites in Fe–N–C catalysts are widely accepted as the main active sites for the oxygen reduction reaction (ORR). Introducing sulfur (S)-functionalities in the carbon to tailor FeN x active centers can further promote their ORR performance in acidic media. Here, we report an approach to synthesize the FeN4 active sites supported on N/S-codoped graphitic carbon (FeN4/NSC) by the in situ addition of thiourea molecules into Fe-doped zeolitic imidazole framework (ZIF-8) precursors and subsequent pyrolysis. The thiourea molecules positively provoke changes in the catalyst structure, including S-doping into the graphitic carbon, improved density of FeN4 active sites, and an increase in the Brunauer–Emmett–Teller surface area (up to 760 m2 g–1). FeN4/NSC exhibits an enhanced ORR activity with a higher half-wave potential of 0.83 V (vs reversible hydrogen electrode (RHE)) compared to that of pristine FeN4/NC (0.80 V), in addition to superior durability with a small activity decay that occurs after 40 000 cycles. The improved catalytic performance is mainly due to the high site density of FeN4 sites and electron-withdrawing S-doping.

The thermodynamic simulation shows that the deposition driving force is greatest for high carbon to hydrogen ratios and reaches a maximum around 850 °C.

Chemical vapour deposition (CVD) is the most promising graphene synthesis route for film and electronic applications but the growth mechanism is still not fully understood. Herein, we investigate the role of the solubility of carbon in the underlying growth substrate on the CVD growth of graphene. A range of Cu-Ni alloys compositions that cover the carbon (C) solubility range between low C solubility (pure Cu) and high C solubility (pure Ni) were used as the catalytic growth substrates. The CVD of graphene on Cu-Ni alloys showed a transition from bilayer graphene (BLG) to few-layer graphene (FLG) at a substrate Ni concentration of 45 wt.%, which was attributed to an increase in the bulk diffusion of C. The Cu-rich alloys had a high graphene coverage (BLG) at a fast-cooling rate (367 °C/min), while the Ni-rich alloys had a low coverage (FLG) under the same cooling condition. In contrast, at slow cooling rates (27 °C/min), the Cu-rich alloys had a low coverage of graphene (BLG) and the Ni-rich alloys had a high coverage of graphene (FLG). Glow discharge optical emission spectroscopy (GDOES) was used to profile the subsurface composition, particularly the C concentration, as a function of depth.