Junyi Ji

Enhanced rate capability of a lithium ion battery anode based on liquid–solid-solution assembly of Fe2O3 on crumpled graphene

We report a liquid–solid-solution assemble strategy to fabricate Fe2O3@graphene (Fe2O3@rGO) composites at the oil/water interface, where the Fe2O3 nanoplates with thickness of about 100 nm are anchored on crumpled graphene sheets. The in situ nucleation and growth process can ensure intimate contact between Fe2O3 nanoplates and graphene sheets, while the oil shell on Fe2O3 can prevent the aggregation of the Fe2O3@rGO composite. The crumpled structure and the relatively thin Fe2O3 nanoplates can shorten the electron diffusion path and enhanced the utilization rate of the active material. When used as the anode material, the Fe2O3@rGO anode shows a high reversible capacity of 1160 mA h g−1 at 0.2 A g−1 after 100 cycles, as well as a high cycling stability (101.3% capacity retention after 300 cycles at 1 A g−1). Moreover, with ∼156 s charging time (at a current density of 12.8 A g−1), the anode can deliver a significant capacity of 552 mA h g−1, indicating its promising application as a high-rate lithium ion battery anode.

N-Doping of plasma exfoliated graphene oxide via dielectric barrier discharge plasma treatment for the oxygen reduction reaction

Nitrogen doped plasma exfoliated graphene oxide (N-PEGO) was obtained by fast and effective dielectric barrier discharge (DBD) plasma technology. The plasma treatment could provide a burst open and high-energy electron/ion collision mechanism for doping and exfoliation. Ammonium carbonate was previously inserted into the interlayer of GO powder, and the rapid release of the NH3 and CO2 gases during DBD plasma treatment could exfoliate the GO powder into few-layer PEGO (<4 layers). Moreover, the plasma treatment also introduced the nitrogen dopant (5.26 at%), which is proven to be an efficient strategy to enhance the performance of oxygen reduction reaction (ORR) electrocatalysts. The resulting N-PEGO showed a high onset potential comparable to that of commercial Pt/C, i.e., 0.89 V vs. reversible hydrogen electrode (RHE) and good electrocatalysis stability towards the ORR. This fast and effective one-step doping and exfoliation strategy demonstrated a new industrial-scale N-doped graphene fabrication technique.

Controllable synthesis of MnO2 nanostructures anchored on graphite foam with different morphologies for a high-performance asymmetric supercapacitor

MnO2 nanostructures with different morphologies (nanowires, nanowire bundles and flower-like nanosheet bundles) were synthesized by adjusting the concentration of KMnO4 solution using a simple and surfactant-free hydrothermal method. Both MnO2 nanowires and nanosheets have ultrathin thickness of about 10–30 nanometers. Such ‘open’ nanostructures can facilitate the electrolyte infiltration and increase the active material utilization efficiency. Owing to the high electron conductivity of the graphene/Ni foam (GNF) substrate as well as the large electrolyte/electrode contact interface, a specific capacitance of 201 F g−1 can be obtained in 1 M Na2SO4 electrolyte. An asymmetric supercapacitor assembled with flower-like MnO2 nanosheet bundles on GNF and activated microwave exfoliated graphite oxide (a-MEGO) yields an energy density of 44.5 W h kg−1 and a power density of 50.0 kW kg−1, respectively. These unique and controllable MnO2 nanostructures may have enormous potential applications in the fields of energy storage and sensors.

Nitrogen-doped porous carbon materials generated via conjugated microporous polymer precursors for CO2 capture and energy storage

Heteroatom doping and well-tuned porosity are regarded as two important factors of porous carbon materials (PCMs) for various applications. However, it is still difficult to tune a single variable while retaining the other factors unchanged, which restricts rational and systematic research on PCMs. In this work, in situ nitrogen-doped porous carbon material (NPCM-1) and its non-doped analogue PCM-1 were prepared by direct pyrolysis of conjugated microporous polymer precursors (TCMP-1 and CMP-1 respectively) with the same skeleton structure. It was found that the CO2 adsorption capability of the PCMs was significantly enhanced compared with their CMP precursors thanks to the optimized pore configuration. Meanwhile, NPCM-1 exhibits much better performance in supercapacitive energy storage than PCM-1 even though these two PCMs possess comparable porosity properties, which is probably due to the much improved electrical conductivity and wettability with the electrolytes because of the introduction of nitrogen doping. Thus, this work provides a valuable insight into the design and preparation of high performance PCMs for CO2 capture and energy storage applications.

Co-doped Ni3S2@CNT arrays anchored on graphite foam with a hierarchical conductive network for high-performance supercapacitors and hydrogen evolution electrodes

Engineering the surface structure and constructing a suitable internal conductive network is essential for the electron transfer rate and the active material utilization efficiency of an electrode. Here, high-porosity carbon nanotube (CNT) arrays grown on graphite foam (GNF) are synthesized via the self-sacrificial ZnO nanorod template. Then three-dimensional Co-doped Ni3S2 nanostructures (Co–Ni3S2) are coated on the CNT surface via a simple hydrothermal process. The CNTs/GNF hybrid with a hierarchical conductive network exhibits good electrical conductivity, while the tectorum-like Co–Ni3S2 nanosheet structure may facilitate both the ion and electron transfer in the redox process. Therefore, the Co–Ni3S2@CNTs/GNF composite shows a highest specific capacitance of 4.1 F cm−2, good rate performance (57.8% capacitance retention from 1 to 40 mA cm−2) and cycling stability (89.8% capacitance retention after 1000 cycles). Moreover, the Co–Ni3S2@CNT/GNF electrode also reveals good hydrogen evolution reaction activity in alkaline solution (an overpotential of 155 mV at 10 mA cm−2).