Browsing by Author "Zhao, S"

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    Controlled one‐pot synthesis of nickel single atoms embedded in carbon nanotube and graphene supports with high loading
    (Wiley, 2020-04-09) Zhao, S; Wang, T; Zhou, G; Zhang, L; Lin, C; Veder, JP; Johannessen, B; Saunders, M; Yin, L; Liu, C; De Marco, R; Yang, SZ; Zhang, Q; Jiang, SP
    Single‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C3N4, g‐C3N4−Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C3N4−Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C3N4‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO2 reduction reaction (CO2RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs. © 1999-2024 John Wiley & Sons, Inc or related companies. All rights reserved.
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    Unsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO2
    (Elsevier, 2019-04) Cheng, Y; Zhao, S; Li, H; He, S; Veder, JP; Johannessen, B; Xiao, J; Lu, S; Pan, J; Chisholm, MF; Yang, SZ; Liu, C; Chen, JG; Jiang, SP
    Supported single atom catalysts (SACs), emerging as a new class of catalytic materials, have been attracting increasing interests. Here we developed a Ni SAC on microwave exfoliated graphene oxide (Ni-N-MEGO) to achieve single atom loading of ∼6.9 wt%, significantly higher than previously reported SACs. The atomically dispersed Ni atoms, stabilized by coordination with nitrogen, were found to be predominantly anchored along the edges of nanopores (< 6 nm) using a combination of X-ray absorption spectroscopy (XAS) and aberration-corrected scanning transmission electron microscopy (AC-STEM). The Ni-N-MEGO exhibits an onset overpotential of 0.18 V, and a current density of 53.6 mA mg−1 at overpotential of 0.59 V for CO2 reduction reaction (CO2RR), representing one of the best non-precious metal SACs reported so far in the literature. Density functional theory (DFT) calculations suggest that the electrochemical CO2-to-CO conversion occurs more readily on the edge-anchored unsaturated nitrogen coordinated Ni single atoms that lead to enhanced activity toward CO2RR. © 2018 Elsevier B.V. All rights reserved.