Insight into the Effect of ZIF-8 Particle Size on the Performance in Nanocarbon-Based Supercapacitors.

Carbon materials derived from zeolitic imidazolate framework-8 (ZIF-8) and composites thereof have been intensively investigated in supercapacitors. The particle size of the used ZIF-8 ranges from dozens of nanometers to several microns. However, the influence of the particle size of ZIF-8 on the capacitive performances is still not clear. A series of ZIF-8 with different particle sizes (from 25 to 296 nm) has been synthesized and carbonized for supercapacitors. Based on TEM, EDX mapping, XRD, Raman, nitrogen adsorption-desorption, XPS, and the results of electrochemical tests, the optimal particle size (≈70 nm) for superior supercapacitor performances in both acidic and alkaline electrolytes has been obtained. This important result provides a significant reference to guide future ZIF-8 related research to achieve the best electrochemical performance.

Hierarchical porous carbon sheets derived on a MgO template for high-performance supercapacitor applications.

Carbon-based supercapacitors have attracted considerable academic and practical interest due to their advantages of low cost, high power density, and superior durability. Herein, we report the facile synthesis of hierarchical porous carbon sheets (HPCSs) featuring a high specific surface area (2788 m2 g-1), derived from pyrrole through a combination of MgO template carbonization and KOH activation. The hierarchical pores with the co-existence of micropores and mesopores were obtained in the HPCSs. Benefiting from the high surface area, well-balanced pore size distribution as well as high conductivity, the prepared HPCSs exhibited a high gravimetric specific capacitance of 226.4 F g-1 at a scan rate of 1 mV s-1 in the electrolyte of 1 M H2SO4 in the two-electrode configuration. Moreover, the excellent electrochemical long-cycle stability has been demonstrated by 10 000 cycles of rapid charging-discharging at 10 A g-1 with a capacitance retention of 97.3%. The electrochemical performance clearly indicates the promising potential of using HPCSs as electrode materials for supercapacitors.

Intumescent flame retardants inspired template-assistant synthesis of N/P dual-doped three-dimensional porous carbons for high-performance supercapacitors.

Heteroatom-doped three-dimensional (3D) porous carbons possess great potential as promising electrodes for high-performance supercapacitors. Inspired by the inherent features of intumescent flame retardants (IFRs) with universal availability, rich heteroatoms and easy thermal-carbonization to form porous carbons, herein we proposed a self-assembling and template self-activation strategy to produce N/P dual-doped 3D porous carbons by nano-CaCO3 template-assistant carbonization of IFRs. The IFRs-derived carbon exhibited large specific surface area, well-balanced hierarchical porosity, high N/P contents and interconnected 3D skeleton. Benefitting from these predominant characteristics on structure and composition, the assembled supercapacitive electrodes exhibited outstanding electrochemical performances. In three-electrode 6 M KOH system, it delivered high specific capacitances of 407 F g-1 at 0.5 A g-1, and good rate capability of 61.2% capacitance retention at 20 A g-1. In two-electrode organic EMIMBF4/PC system, its displayed high energy density of 62.8 Wh kg-1 at a power density of 748.4 W kg-1, meanwhile it had excellent cycling stability with 84.7% capacitance retention after 10,000 cycles. To our best knowledge, it is the first example to synthesize porous carbon from IFRs precursor. Thus, the current work paved a novel and low-cost way for the production of high-valued carbon material, and expanded its application for high-performance energy storage devices.

Co-etching effect to convert waste polyethylene terephthalate into hierarchical porous carbon toward excellent capacitive energy storage.

With the ever-increasing consumption of polyethylene terephthalate (PET) related products, how to recycle the waste PET still remains as a great challenge for the sustainable development. Converting waste PET into porous carbon material has been emerged as a promising way to address this issue. Recently, the microporous carbon derived from waste PET has drawn considerable attention in adsorption field, but its electrochemical application is still impeded by low specific surface area (SSA <1500 m2 g-1) and small meso-/macropores volume (<0.2 cm3 g-1). Herein, hierarchical porous carbon (HPC) is successfully prepared from waste PET. The obtained HPC possesses a high SSA (2238 m2 g-1) and a large meso-/macropores volume (0.51 cm3 g-1). The formation mechanism of hierarchical porous structure is proposed: co-etching effect of sp2/sp3 hybridized carbon produces micropores and meso-/macropores, respectively. In a three-electrode configuration, HPC based electrode achieves an outstanding capacitance of 413 F g-1, while the traditional microporous carbon exhibits a low capacitance of 142 F g-1. The fabricated symmetric supercapacitor shows a high energy density of 25 Wh kg-1. This work provides a good reference to convert waste plastics into hierarchical porous carbon.

Eucalyptus derived heteroatom-doped hierarchical porous carbons as electrode materials in supercapacitors.

Carbon-based supercapacitors have aroused ever-increasing attention in the energy storage field due to high conductivity, chemical stability, and large surface area of the investigated carbon active materials. Herein, eucalyptus-derived nitrogen/oxygen doped hierarchical porous carbons (NHPCs) are prepared by the synergistic action of the ZnCl2 activation and the NH4Cl blowing. They feature superiorities such as high specific surface area, rational porosity, and sufficient N/O doping. These excellent physicochemical characteristics endow them excellent electrochemical performances in supercapacitors: 359 F g-1 at 0.5 A g-1 in a three-electrode system and 234 F g-1 at 0.5 A g-1 in a two-electrode system, and a high energy density of 48 Wh kg-1 at a power density of 750 W kg-1 accompanied by high durability of 92% capacitance retention through 10,000 cycles test at a high current density of 10 A g-1 in an organic electrolyte. This low-cost and facile strategy provides a novel route to transform biomass into high value-added electrode materials in energy storage fields.

High yield conversion of biowaste coffee grounds into hierarchical porous carbon for superior capacitive energy storage.

Recently great efforts have been focused on converting biowastes into high-valued carbon materials. However, it is still a great challenge to achieve high carbon yield and controllable porous distribution in both industrial and academic research. Inspired by the multi-void structure of waste coffee grounds, herein we fabricated hierarchical porous carbon via the combination of catalytic carbonization and alkali activation. The catalytic carbonization process was applied to obtain well-defined mesoporous carbon with carbon yield as high as 42.5 wt%, and subsequent alkali activation process produced hierarchical porous carbon with ultrahigh specific surface area (3549 m2 g-1) and large meso-/macropores volume (1.64 cm3 g-1). In three-electrode system, the electrode exhibited a high capacitance of 440 F g-1 at 0.5 A g-1 in 6 M KOH aqueous electrolyte, superior to that of many reported biomass-derived porous carbons. In two-electrode system, its energy density reached to 101 Wh kg-1 at the power density of 900 W kg-1 in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIMBF4). This work provided a cost-effective strategy to recycle biowastes into hierarchical porous carbon with high yield for high-performance energy storage application.

Mass production of hierarchically porous carbon nanosheets by carbonizing "real-world" mixed waste plastics toward excellent-performance supercapacitors.

Recently, sustainable development and serious energy crisis called for appropriate managements for the large number of municipal and industrial waste plastics as well as the development of low-cost, advanced materials for energy storage. However, the complexity of waste plastics significantly hampers the application of ever used methods, and little attention is paid to the utilization of waste plastics-derived carbon in energy storage. Herein, porous carbon nanosheets (PCNSs) was produced by catalytic carbonization of "real-world" mixed waste plastics on organically-modified montmorillonite (OMMT) and the subsequent KOH activation. PCNSs was featured on hierarchically micro-/mesoporous structures with the pore size distribution centered on 0.57, 1.42 and 3.63 nm and partially exfoliated graphitic layers, and showed a high specific surface area of 2198 m2 g-1 and a large pore volume of 3.026 cm3 g-1. Benefiting from these extraordinary properties, PCNSs displayed a superior performance for supercapacitors with high specific capacitances approaching 207 and 120 F g-1 at a current density of 0.2 A g-1 in aqueous and organic electrolytes, respectively. Importantly, when the current density increased to 10 A g-1, the specific capacitances remained at 150 F g-1 (72.5%) and 95 F g-1 (79.2%) in aqueous and organic electrolytes, respectively. The outstanding rate capability of PCNSs was in sharp contrast to the performance of traditional activated carbons. This work not only provides a potential way to recycle mixed waste plastics, but also puts forward a facile sustainable approach for the large-scale production of PCNSs as a promising candidate for supercapacitors.

A novel 3D Cu(I) coordination polymer based on Cu6Br2 and Cu2(CN)2 SBUs: in situ ligand formation and use as a naked-eye colorimetric sensor for NB and 2-NT.

A novel coordination polymer with the chemical formula [Cu4Br(CN)(mtz)2]n (mtz = 5-methyl tetrazole) (), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectroscopy, thermal gravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. Interestingly, the Cu(i), CN(-) and mtz(-) in compound are all generated from an in situ translation of the original precursors: Cu(2+), acetonitrile and 1-methyl-5-mercapto-1,2,3,4-tetrazole (Hmnt). The in situ ring-to-ring conversion of Hmnt into mtz(-) was found for the first time. Structural analysis reveals that compound is a novel 3D tetrazole-based Cu(i) coordination polymer, containing both metal halide cluster Cu6Br2 and metal pseudohalide cluster Cu2(CN)2 secondary building units (SBUs), which shows an unprecedented (3,6,10)-connected topology. Notably, a pseudo-porphyrin structure with 16-membered rings constructed by four mtz(-) anions and four copper(i) ions was observed in compound . The fluorescence properties of compound were investigated in the solid state and in various solvent emulsions, the results show that compound is a highly sensitive naked-eye colorimetric sensor for NB and 2-NT (NB = nitrobenzene and 2-NT = 2-nitrotoluene).