A Layered‐Nanospace‐Confinement Strategy for the Synthesis of Two‐Dimensional Porous Carbon Nanosheets for High‐Rate Performance Supercapacitors

A general approach is developed for the synthesis of 2D porous carbon nanosheets (PCNS) from bio‐sources derived carbon precursors (gelatin) by an integrated procedure of intercalation, pyrolysis, and activation. Montmorillonite with layered nanospace is used as a nanotemplate or nanoreactor to confine and modulate the transformation of gelatin, further leading to the formation of 2D nanosheet‐shaped carbon materials. The as‐made 2D PCNS exhibits a significantly improved rate performance, with a high specific capacitance of 246 F g^?1 and capacitance retention of 82% at 100 A g^?1, being nearly twice that of microsized activated carbon particulates directly from gelatin (131 F g^?1, 44%). The shortened ion transport distance in the nanoscaled dimension and modulated porous structure is responsible for such an enhanced superior rate capability. More importantly, the present strategy can be extended to other bio‐sources to create 2D PCNS as electrode materials with high‐rate performance. This will also provide a potential strategy for configuring 2D nanostructured carbon electrode materials with a short ion transport distance for supercapacitors and other carbon‐related energy storage and conversion devices.     

Land‐use conversion and changing soil carbon stocks in China's ‘Grain‐for‐Green’ Program: a synthesis

The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the ‘Grain‐for‐Green’ Program to determine which factors were driving changes to soil organic carbon (SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0–100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0–20 cm) than in deeper soil (20–100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long‐term, and therefore, the large scale of land‐use change under the ‘Grain‐for‐Green’ Program will significantly increase China's C stocks.     

Homo‐C‐nucleoside analogs IV. Synthesis of 4‐(2,5‐anhydro‐D‐altro‐pentitol‐1‐yl)‐2‐phenyl‐2H‐1,2,3‐triazole homo‐C‐nucleoside. CD assignment of the absolute configuration of the carbon bridge

Dehydrative cyclization of 4‐(D‐altro ‐pentitol‐1‐yl)2‐phenyl‐2H ‐1,2,3‐triazole in basic medium with one moler equivalent of p‐toluene sulfonyl chloride in pyridine solution gave the homo‐C‐ nucleoside 4‐(2,5‐anhydro‐D‐altro ‐1‐yl)‐2‐phenyl‐2H ‐1,2,3‐triazole. The structure and anomeric configuration was determined by acylation, nuclear magnetic resonance (NMR), and mass spectroscopy. The stereochemistry at the carbon bridge of homo‐C‐ nucleoside 2‐phenyl‐2H ‐1,2,3‐triazoles was determined by circular dichroism (CD) spectroscopy.     

Spontaneous Growth of 3D Framework Carbon from Sodium Citrate for High Energy‐ and Power‐Density and Long‐Life Sodium‐Ion Hybrid Capacitors

Carbon sheets with 3D architectures, large graphitic interlayer spacing, and high electrical conductivity are highly expected to be an ideal anode material for sodium‐ion hybrid capacitors (SIHCs). Pursuing a simple synthesis methodology and advancing it from the laboratory to industry is of great importance. In this study, a new approach is presented to prepare 3D framework carbon (3DFC) with the above integrated advantages by a direct calcination of sodium citrate without aid of any additional carbon source, template, or catalyst. The first‐principle calculations verify that the large interlayer spacing and the curvature structure of 3DFC facilitate the sodium ion insertion/extraction. As a consequence, the optimal 3DFC sample exhibits high reversible capacity as well as excellent rate and cycling performance. On this basis, a dual‐carbon SIHC is fabricated by employing 3DFC as battery‐type anode and 3DFC‐derived nanoporous carbon as capacitor‐type cathode. It is able to deliver high energy‐ and power‐density feature as well as outstanding long‐term cycling stability in the potential range of 0–4.0 V. This study may open an avenue for developing high‐performance carbon electrode materials and pushes the practical applications of SIHCs a decisive step forward.     

Metal‐Organic Framework‐Derived Carbons for Battery Applications

The applications of carbon and carbon‐based materials with high porosity, high surface area, and functionalities based on metal‐organic framework precursors and/or templates have attracted significant research interest in recent years, particularly in the field of batteries. The chemical and physical properties of carbon and carbon‐based materials obtained by the heat treatment of various metal‐organic framework precursors or templates are improved to a certain extent. In this comprehensive review, the synthetic methods and electrochemical performance of carbon materials derived from metal‐organic frameworks (metal/carbon, metal oxide/carbon, nitrogen‐doped carbon, porous carbon, etc.) along with their applications in batteries are outlined.     

High‐Efficiency Large‐Area Carbon Nanotube‐Silicon Solar Cells

Currently studied carbon nanotube‐silicon (CNT‐Si) solar cells are based on relatively small active areas (typically <0.15 cm²); increasing the active area generally leads to reduced power conversion efficiencies. This study reports CNT‐Si solar cells with active areas of more than 2 cm² for single cells, yet still achieving cell efficiencies of about 10%, which is the first time for CNT‐Si solar cells with an active area more than 1 cm² to reach the level for real applications. In this work, a controlled number of flattened highly conductive CNT strips is added, in simple arrangement, to form a CNT‐Si solar cell with CNT strips in which the middle film makes heterojunctions with Si while the top strips act as self‐similar top electrodes, like conventional metal grids. The CNT strips, directly condensed from as‐grown CNT films, not only improve the CNT‐Si junctions, but also enhance the conductivity of top electrodes without introducing contact barrier when the CNT strips are added onto the film. This property may facilitate the development of large‐area high‐performance CNT or graphene‐Si solar cells.     

Paper‐Based Energy‐Storage Devices Comprising Carbon Fiber‐Reinforced Polypyrrole‐Cladophora Nanocellulose Composite Electrodes

Composites of polypyrrole (PPy) and Cladophora nanocellulose, reinforced with 8 μm‐thick chopped carbon filaments, can be used as electrode materials to obtain paper‐based energy‐storage devices with unprecedented performance at high charge and discharge rates. Charge capacities of more than 200 C g^?1 (PPy) are obtained for paper‐based electrodes at potential scan rates as high as 500 mV s^?1, whereas cell capacitances of ～60–70 F g^?1 (PPy) are reached for symmetric supercapacitor cells with capacitances up to 3.0 F (i.e.,0.48 F cm^?2) when charged to 0.6 V using current densities as high as 31 A g^?1 based on the PPy weight (i.e., 99 mA cm^?2). Energy and power densities of 1.75 Wh kg^?1 and 2.7 kW kg^?1, respectively, are obtained when normalized with respect to twice the PPy weight of the smaller electrode. No loss in cell capacitance is seen during charging/discharging at 7.7 A g^?1 (PPy) over 1500 cycles. It is proposed that the nonelectroactive carbon filaments decrease the contact resistances and the resistance of the reduced PPy composite. The present straightforward approach represents significant progress in the development of low‐cost and environmentally friendly paper‐based energy‐storage devices for high‐power applications.     

Beavers affect carbon biogeochemistry: both short‐term and long‐term processes are involved

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Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

Biotransformation of carbon tetrachloride by various acetate‐ and nitrate‐limited denitrifying consortia

Fed‐batch experiments were performed to determine the carbon tetrachloride (CT)‐degrading ability of three denitrifying consortia cultured from sites not contaminated with CT. A mathematical model was used to quantify the rates of CT transformation by the consortia under both acetate‐limiting and nitrate‐limiting conditions. A rate constant for CT transformation on a cellular protein basis and the fraction of degraded CT transformed to chloroform (CF) were determined for each consortium by optimizing the model to fit the experimental data. The parameters for these experiments were statistically compared to those obtained for previous experiments with a denitrifying consortium cultured from an aquifer soil sample from the US Department of Energy Hanford site in southeastern Washington state. Results of F‐test analysis indicated the rate of CT transformation and the production of CF both were functions of the limiting nutrient. Under nitrate‐limited conditions, the rate constant for CT transformation for all four consortia was about 30 L/gmol/min and approximately 50% of the CT transformed was converted to CF. When acetate was the limiting nutrient, the rate constant for CT transformation was approximately 8 L/gmol/min and the CF yield decreased to about 25%. These results imply the ability to degrade CT may be inherent to some denitrifying organisms, regardless of previous exposure to CT. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 342–348, 1999.     

Toward a Low‐Cost Artificial Leaf: Driving Carbon‐Based and Bifunctional Catalyst Electrodes with Solution‐Processed Perovskite Photovoltaics

Molecular hydrogen can be generated renewably by water splitting with an “artificial‐leaf device”, which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovoltaics. Ideally, this device should operate efficiently and be fabricated with cost‐efficient means using earth‐abundant materials. Here, a lightweight electrocatalyst electrode, comprising large surface‐area NiCo₂O₄ nanorods that are firmly anchored onto a carbon–paper current collector via a dense network of nitrogen‐doped carbon nanotubes is presented. This electrocatalyst electrode is bifunctional in that it can efficiently operate as both anode and cathode in the same alkaline solution, as quantified by a delivered current density of 10 mA cm^?2 at an overpotential of 400 mV for each of the oxygen and hydrogen evolution reactions. By driving two such identical electrodes with a solution‐processed thin‐film perovskite photovoltaic assembly, a wired artificial‐leaf device is obtained that features a Faradaic H₂ evolution efficiency of 100%, and a solar‐to‐hydrogen conversion efficiency of 6.2%. A detailed cost analysis is presented, which implies that the material‐payback time of this device is of the order of 100 days.     

Amphicharge‐Storable Pyropolymers Containing Multitiered Nanopores

In this study, hierarchically nanoporous pyropolymers (HN‐PPs) including numerous redox‐active heteroatoms are fabricated from polyaniline nanotubes by heating with KOH. In the large operating voltage range 1.0–4.8 V versus Li⁺/Li, HN‐PPs store amphicharges by a pseudocapacitive manner of Li‐ion (mainly <3.0 V) and electrochemical double layer formation of anion (primarily >3.0 V). Through these surface‐driven charge storage behaviors, HN‐PPs achieve a significantly high specific capacity of ≈460 mA h g^?1 at 0.5 A g^?1, maintaining specific capacities of 140 mA h g^?1 at a high specific current of 30 A g^?1 and 305 mA h g^?1 after 2000 cycles at 3 A g^?1. Furthermore, asymmetric energy storage devices based on HN‐PPs deliver a high specific energy of 265 W h kg^?1 and high specific power of 5081 W kg^?1 with long‐term cycling performance.