Jianglin Ye

Assembling carbon quantum dots to a layered carbon for high-density supercapacitor electrodes

It is found that carbon quantum dots (CQDs) self-assemble to a layer structure at ice crystals-water interface with freeze- drying. Such layers interconnect with each other, forming a free-standing CQD assembly, which has an interlayer distance of about 0.366 nm, due to the existence of curved carbon rings other than hexagons in the assembly. CQDs are fabricated by rupturing C60 by KOH activation with a production yield of ~15 wt.%. The CQDs obtained have an average height of 1.14 nm and an average lateral size of 7.48 nm, and are highly soluble in water. By packaging annealed CQD assembly to high density (1.23 g cm−3) electrodes in supercapacitors, a high volumetric capacitance of 157.4 F cm−3 and a high areal capacitance of 0.66 F cm−2 (normalized to the loading area of electrodes) are demonstrated in 6 M KOH aqueous electrolyte with a good rate capability.

Microwave-assisted synthesis of hematite/activated graphene composites with superior performance for photocatalytic reduction of Cr(VI)

Hematite (α-Fe2O3) nanoparticles are deposited onto porous ‘activated microwave expanded graphite oxide’ (aMEGO) carbon via a simple, rapid one-pot microwave process. Under the irradiation of visible light, the α-Fe2O3/aMEGO composites exhibit significantly enhanced photocatalytic activity for the reduction of Cr(VI) to Cr(III). A maximum Cr(VI) removal rate of 95.28% is obtained for the composite containing 7.72 wt% aMEGO as compared to that of 25.26% for pure α-Fe2O3; the rate constant of the composite is nearly 9 times higher than that of pure α-Fe2O3. The crucial role of aMEGO in enhancing the photocatalytic efficiency of the composites relies not only on its large surface area, but also on the high conductivity which benefits the transport of photoexcited electrons. The enhancement in the charge separation and the suppression in the electron–hole pair recombination is evidenced by an increased photocurrent and a suppressed photoluminescence in the α-Fe2O3/aMEGO composites.

Direct Laser Writing of Graphene Made from Chemical Vapor Deposition for Flexible, Integratable Micro‐Supercapacitors with Ultrahigh Power Output

High-performance yet flexible micro-supercapacitors (MSCs) hold great promise as miniaturized power sources for increasing demand of integrated electronic devices. Herein, this study demonstrates a scalable fabrication of multilayered graphene-based MSCs (MG-MSCs), by direct laser writing (DLW) of stacked graphene films made from industry-scale chemical vapor deposition (CVD). Combining the dry transfer of multilayered CVD graphene films, DLW allows a highly efficient fabrication of large-areal MSCs with exceptional flexibility, diverse planar geometry, and capability of customer-designed integration. The MG-MSCs exhibit simultaneously ultrahigh energy density of 23 mWh cm-3 and power density of 1860 W cm-3 in an ionogel electrolyte. Notably, such MG-MSCs demonstrate an outstanding flexible alternating current line-filtering performance in poly(vinyl alcohol) (PVA)/H2 SO4 hydrogel electrolyte, indicated by a phase angle of -76.2° at 120 Hz and a resistance-capacitance constant of 0.54 ms, due to the efficient ion transport coupled with the excellent electric conductance of the planar MG microelectrodes. MG-polyaniline (MG-PANI) hybrid MSCs fabricated by DLW of MG-PANI hybrid films show an optimized capacitance of 3.8 mF cm-2 in PVA/H2 SO4 hydrogel electrolyte; an integrated device comprising MG-MSCs line filtering, MG-PANI MSCs, and pressure/gas sensors is demonstrated.

Diameter-Sensitive Breakdown of Single-Walled Carbon Nanotubes upon KOH Activation

While potassium hydroxide (KOH) activation has been used to create pores in carbon nanotubes (CNTs) for improved energy-storage performance, the KOH activation mechanism of CNTs has been rarely investigated. In this work, the reaction between single-walled CNTs (SWCNTs) and KOH is studied in situ by thermogravimetric analysis coupled to infrared (IR) spectroscopy and gas chromatography/mass spectrometry (MS). The IR and MS results clearly demonstrate the sequential evolution of CO, hydrocarbons, CO2 , and H2 O in the activation process. By using the radial breathing mode of Raman spectroscopy, a diameter-sensitive selectivity is observed in the reaction between SWCNTs and KOH, leading to a preferential distribution of SWCNTs with diameters larger than 1 nm after activation at 900 °C and a preferential removal of SWCNTs with diameters below 1 nm upon activation.

Tailoring the Structure of Carbon Nanomaterials toward High‐End Energy Applications

Carbon nanomaterials are perceived to be ideally suited candidates for high-end energy applications, owing to their unparalleled advantages including superior electric and thermal conductivity, excellent mechanical properties, and high specific surface areas. It has been demonstrated through several research contributions that the electrochemical performance of carbon nanomaterials significantly depends upon their versatile electronic structures and microstructures. These can be precisely tailored by rational defect engineering, heteroatom doping, heterostructure coupling, and pore fabrication, which largely affect the intrinsic nature of active sites and facilitate the ion/electron transfer. Herein, the recent progress in tailoring carbon nanostructures toward high-end electrocatalysis and supercapacitor applications is summarized, with an emphasis on synthesis strategies, advanced characterizations, and specific elucidation of structure-performance relationship. The challenges and opportunities for the rational design and detection of variously tailored carbon nanomaterials that can further improve the fundamental understanding and practical applications in the field of energy storage and conversion are also discussed.

Solid-state yet flexible supercapacitors made by inkjet-printing hybrid ink of carbon quantum dots/graphene oxide platelets on paper

Paper-based flexible supercapacitors (SCs) show advantages due to the improved adhesion between paper and active materials, the simplified printing process and the lower cost, compared to other substrates such as plastics. Here we report the fabrication of solid-state yet flexible SCs by inkjetprinting a hybrid ink consisting of carbon quantum dots (CQDs) and graphene oxide (GO) platelets, followed by casting of polyvinyl alcohol (PVA)/sulfuric acid (H2SO4) gel electrolyte. The SC obtained from 100-time-printing of the hybrid ink shows a specific capacitance of ~1.0 mF cm−2 at a scan rate of 100 mV s−1, which is enhanced by nearly 150%; the whole device including paper substrate, gel electrolyte and active material demonstrates an energy density of 0.078 mW h cm−3 at a power density of 0.28 mW cm−3. In addition, the excellent mechanical strength of GO platelets ensures the good flexibility and mechanical robustness of the printed SCs, which show a retention of 98% in capacitance after being bended for 1,000 cycles at a bending radius of 7.6 mm. This study demonstrates a promising strategy for the large-scale preparation of low-cost, lightweight, and flexible/wearable energy storage devices based on carbon-based ink and paper substrate.摘要与其他柔性基底材料如塑料相比, 纸基柔性超级电容器具有印刷工艺简单、 制造价格低廉以及基底和活性材料之间具有更好的粘合力等优势. 在这里, 我们通过喷墨打印碳量子点(CQDs)和氧化石墨烯(GO)组成的混合墨水、 采用PVA/H2SO4为凝胶电解质制备了固态柔性超级电容器, 并对其性能进行了系统研究. 打印100次混合墨水获得的超级电容器在100 mV s−1的扫描速率下显示出~1.0 mF cm−2的比电容, 相比于纯GO墨水制备的超级电容器其比电容增加了150%; 通过进一步优化, 基于超级电容器整个装置(包括纸基、 凝胶电解质和活性材料)在0.28 mW cm−3的功率密度下表现出0.078 mW h cm−3的能量密度. 此外, GO薄片具有出色的机械强度, 确保超级电容器具有良好的柔韧性和机械强度, 在弯曲半径为7.6 mm的条件下弯曲1000次后, 仍保留98%的电容. 基于碳基墨水和纸张基材的喷墨打印的技术为低成本、 轻便、 灵活/可穿戴式储能装置的大规模制备提供了可能.

Enhanced physical properties of γ-Al2O3–rGO hybrids prepared by solvothermal and hot-press processing

In this study, a solvothermal method was employed for the first time to fabricate hybrids composed of cross-linked γ-Al2O3 nanorods and reduced graphite oxide (rGO) platelets. After calcination and hot-press processing, monoliths of Al2O3–rGO hybrids were obtained with improved physical properties. It was found that the oxygen-containing groups on graphene oxide were beneficial for the adsorption of aluminum isopropoxide, leading to a uniform dispersion of rGO with Al2O3, which was obtained by hydrolysis of aluminum isopropoxide during the solvothermal reaction. The hybrid, which was subsequently calcinated for 3 h showed electrical conductivity of 6.7 × 101 S m−1 together with 90% higher mechanical tensile strength and 80% higher thermal conductivity as compared to the bare Al2O3. In addition, the dielectric constant of the hybrid was 12 times higher than that of the bare Al2O3. In this study, the highest values of electrical conductivity (8.2 × 101 S m−1), thermal conductivity (2.53 W m−1 K−1), dielectric constant (104) and Youngs modulus (3.7 GPa) were obtained for the alumina–rGO hybrid calcinated for 1 h. XRD characterization showed that an increase in calcination temperature and further hot-press processing at 900 °C led to enhanced crystallinity in the γ-Al2O3 nanorods in the hybrid, resulting in enhanced physical properties in the hybrids.

Hierarchical porous carbon obtained from frozen tofu for efficient energy storage

Frozen tofu, as a carbon and nitrogen source, is converted to N (0.6–6.7 at%) and O (3.6–9.5 at%) co-doped porous carbon with a specific surface area of up to 3134 m2 g−1 by one-step carbonization-activation. This hierarchical carbon consists of a high volume of mesopores (1.11 cm3 g−1) and micropores (0.71 cm3 g−1) with a typical pore size distribution between 0.8 and 4 nm. Supercapacitors with the obtained carbon as electrodes exhibit a specific capacitance of 243 F g−1 (measured at 0.1 A g−1) in 1 M sulfuric acid (H2SO4) aqueous electrolyte with a capacitance retention of 93% after 10 000 cycles at 10 A g−1. The carbon also exhibits a specific capacitance of 170 F g−1 (measured at 1 A g−1) with a good rate capability (135 F g−1 at 20 A g−1) in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) ionic liquid electrolyte, providing an energy density of 72 W h kg−1 (at an average power density of 889 W kg−1). A supercapacitor fabricated from the carbon in the ionic liquid electrolyte can readily power 25 light-emitting diodes in parallel for more than 2 min after being charged for 25 s at a current density of 10 A g-1. In addition, as an anode for Li-ion batteries, the porous carbon exhibits a high reversible charge capacity of 2120 mA h g−1 in the first cycle (measured at 0.1 A g−1) or 1035 mA h g−1 after 300 cycles (measured at 1 A g−1).

Oxygen-Rich Carbon Quantum Dots as Catalysts for Selective Oxidation of Amines and Alcohols

Metal‐free carbocatalysis has been widely utilized for aerobic oxidative reactions. Here, we report that oxygen‐rich carbon quantum dots (O‐CQDs) demonstrate a catalytic performance superior to graphene oxide, if used as a metal‐free nanocatalyst for the direct transformation of amines and alcohols, under mild and solvent‐free conditions. O‐CQDs show a yield of 75 % for the oxidative coupling of amine to imine (with 5 wt % catalyst loading) and a conversion of 3.8 % for benzyl alcohol (with 2 wt % catalyst loading). The catalytic activities of thermally treated O‐CQDs are further improved for benzylamine, for example, indicated by a yield of up to 98 % with 4 wt % catalyst loading. In addition, O‐CQDs show a photoenhanced catalytic ability of amine (98 % yield with 5 wt % catalyst loading for 6 h reaction). Characterizations and simulations show that numerous carboxyl oxygen functional groups and unpaired electrons at the edge sites of O‐CQDs are likely involved in the aerobic oxidation of amines.