Yijin Cai

Three-dimensional honeycomb-like hierarchically structured carbon for high-performance supercapacitors derived from high-ash-content sewage sludge

In this work, we demonstrate for the first time that three-dimensional honeycomb-like hierarchically structured carbon (HSC) can be prepared by using high-ash-content sewage sludge as a carbon precursor. The fly-silicon process plays a crucial role in the formation of honeycomb-like hierarchical structures. The as-resulted HSC exhibits novel honeycomb-like frameworks, high specific surface area (2839 m2 g−1), large pore volume (2.65 cm3 g−1), interconnected hierarchical porosity, and excellent electrochemical performance. The high specific capacitance of 379 F g−1 as well as excellent rate capability and outstanding cycling stability (over 90% capacitance retention after 20 000 cycles even at a high current density of 20 A g−1), makes it suitable for high-performance supercapacitor electrode materials. The assembled HSC//HSC symmetric supercapacitor presents enhanced supercapacitive behavior with a high energy density of 30.5 W h kg−1 in aqueous solution. This strategy provides an effective method to develop high-performance electrode materials derived from other high-ash-content biomass wastes for supercapacitors.

Interconnected 3 D Network of Graphene-Oxide Nanosheets Decorated with Carbon Dots for High-Performance Supercapacitors

Interconnected 3 D nanosheet networks of reduced graphene oxide decorated with carbon dots (rGO/CDs) are successfully fabricated through a simple one-pot hydrothermal process. The as-prepared rGO/CDs present appropriate 3 D interconnectivity and abundant stable oxygen-containing functional groups, to which we can attribute the excellent electrochemical performance such as high specific capacitance, good rate capability, and great cycling stability. Employed as binder-free electrodes for supercapacitors, the resulting rGO/CDs exhibit excellent long-term cycling stability (ca. 92 % capacitance retention after 20 000 charge/discharge cycles at current density of 10 A g-1 ) as well as a maximum specific capacitance of about 308 F g-1 at current density of 0.5 A g-1 , which is much higher than that of rGO (200 F g-1 ) and CDs (2.2 F g-1 ). This work provides a promising strategy to fabricate graphene-based nanomaterials with greatly boosted electrochemical performances by decoration of with CDs.

Ultrahigh-surface-area hierarchical porous carbon from chitosan: acetic acid mediated efficient synthesis and its application in superior supercapacitors

The development of an effective route to high-performance carbonaceous electrode materials derived from low-cost biomass is critical but remains challenging for supercapacitors. Here we propose a new and cost-effective way to produce chitosan-based hierarchical porous carbons by the union of hydrothermal carbonization and chemical activation. The key to this preparation strategy is the utilization of acetic acid as an additive for hydrothermal carbonization, which not only favors the construction of a conducive environment for accessibility of activator KOH, but also leads to the formation of a rigid semi-carbonized framework substrate for generating an ultrahighly porous structure. Thus, our synthetic approach allows for a lower amount of activation agent and lower heating temperature when compared with normal chemical activation techniques, providing a more efficient way to produce ultrahigh-surface-area carbon materials. The as-prepared hierarchical porous carbon possesses a unique honeycomb-like framework and the highest BET surface area of 3532 m2 g−1 among all the carbon materials derived from chitosan. The combination of the hierarchical pore structure for rapid ion diffusion and the ultrahigh surface area for sufficient electrochemically active sites significantly improves the materials capacitive behaviors. An unusually high capacitance of 455 F g−1, an excellent cycling stability with 99% capacity retention over 20 000 cycles in KOH aqueous electrolyte, and a high energy density of 20.6 W h kg−1 at a power density of 226.8 W kg−1 in 1.8 V Na2SO4 aqueous supercapacitors have been obtained, demonstrating that the chitosan-based hierarchical porous carbons developed here are very attractive for application in supercapacitors.

Bioimaging Application and Growth-Promoting Behavior of Carbon Dots from Pollen on Hydroponically Cultivated Rome Lettuce

Carbon dots (CDs) obtained from rapeseed pollen with a high production yield, good biocompatibility, good water solubility, low cost, and simple synthesis are systematically characterized. They can be directly added to Hoagland nutrient solution for planting hydroponically cultivated Lactuca sativa L. to explore their influence on the plants at different concentrations. By measuring lettuce indices of growth, morphology, nutrition quality, gas exchange, and content of photosynthetic pigment, amazing growth-promotion effects of CDs were discovered, and the mechanism was analyzed. Moreover, the in vivo transport route of CDs in lettuce was evaluated by macroscopic and microscopic observations under UV light excitation. The results demonstrate that pollen-derived CDs can be potentially used as a miraculous fertilizer for agricultural applications and as a great in vivo plant bioimaging probe.