Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous ...few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).
Abstract Substantially different from traditional combinatorial-treatment of photothermal therapy (PTT) and photodynamic therapy (PDT) by using multi-component nanocomposite under excitation of ...separate wavelength, a novel single near infrared (NIR) laser-induced multifunctional theranostic nanoplatform has been rationally and successfully constructed by a single component black titania ( B –TiO 2− x ) for effective imaging-guided cancer therapy for the first time. This multifunctional PEGylated B –TiO 2− x shows high dispersity/stability in aqueous solution, excellent hemo/histocompatibility and broad absorption ranging from NIR to ultraviolet (UV). Both in vitro and in vivo results well demonstrated that such a novel multifunctional theranostic nanoplaform could achieve high therapeutic efficacy of simultaneous and synergistic PTT/PDT under the guidance of infrared thermal/photoacoustic (PA) dual-modal imaging, which was triggered by a single NIR laser. This research circumvents the conventional obstacles of using multi-component nanocomposites, UV light and high laser power density. Furthermore, negligible side effects to blood and main tissues could be found in 3 months' investigation, facilitating its potential biomedical application.
The peak fluorescence emission of conventional fluorophores such as organic dyes and inorganic quantum dots is independent of the excitation wavelength. In contrast, the position of the peak ...fluorescence of graphene oxide (GO) in a polar solvent is heavily dependent on the excitation wavelength. The present work has discovered that the strong excitation wavelength dependent fluorescence in GO is originated from the “giant red-edge effect”, which breaks Kasha’s rule. When GO sheets are present in a polar solvent, the solvation dynamics slow down to the same time scale as the fluorescence due to the local environment of the GO sheet. Consequently, the fluorescence peak of GO broadens and red-shifts up to 200 nm with an increase in the excitation wavelength. The giant red-edge effect of GO disappears in a nonpolar solvent, leading to a narrow fluorescence peak that is independent of the excitation wavelength. Discovery of the underlying strong excitation wavelength dependent fluorescence mechanism provides guidelines for the design of graphene oxide-based optical devices.
3D architectures constructed from a tubular graphene network can withstand repeated >95% compression cycling without damage. Aided by intertubular covalent bonding, this material takes full advantage ...of the graphene tube's unique attributes, including complete pre‐ and post‐buckling elasticity, outstanding electrical conductivity, and extraordinary physicochemical stability. A highly connected tubular graphene will thus be the ultimate, structurally robust, ultrastrong, ultralight material.
Here we report a facile low-temperature solvothermal method by using Li-dissolved ethanediamine to prepare uniform hydrogenated blue H-TiO2–x with wide spectrum response. H-TiO2–x possesses a ...distinct crystalline core–amorphous shell structure (TiO2@TiO2–x ) with numerous oxygen vacancies and doped H in the amorphous shell. Efficient solar to chemical energy conversions, likely photocatalytic reduction of CO2, degradation of contaminants, and H2 generation from water splitting can be achieved over this blue titania. Notably, the optimized H-TiO2–x (200) shows high activity of CH4 formation at a rate of 16.2 μmol g–1 h–1 and a selectivity of 79% under full solar irradiation. The kinetic isotope effects measurements reveal that the cleavage of the CO bond from CO2 rather than the O–H bond from H2O is the rate-determining step in CH4 formation. Meanwhile, in situ diffuse reflectance infrared Fourier transform spectroscopy shows the existence of the key intermediate CO2 – species. The formation of intermediate CO2 – indicates that the defective surface of H-TiO2–x can efficiently accelerate the adsorption and chemical activation of the extremely stable CO2 molecule, which makes the single-electron reduction of CO2 to CO2 – easier.
Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge ...towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self‐grown fragments of ⋅NCN⋅ or NCCN and conductive carbon (C‐sp2) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few‐layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp2 carbon (≈65%) favoring a high conductivity (>2 S cm−1); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming NiN bonds. The conductive carbon nitride harvests a large capacitance of 372 F g−1 with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g−1.
Conductive carbon nitride, simultaneously gaining high nitrogen doping and high electrical conductivity, is obtained from novel space‐confined reaction. Nickel hydrogencyanamide provides self‐grown fragments of ⋅NCN⋅ or NC−CN and conductive carbon (C‐sp2) catalyst of Ni metal during the decomposition. The final product is a tubular structure of extraordinarily high N doping level (≈15 at%) and high conductivity (>2 S cm−1).
The 2H molybdenum disulfide (MoS2), as a stable hexagonal phase, has been one of the most studied transition metal dichalcogenides over the past decades. In the last five years, the metastable phases ...of MoS2 (1T, 1T′, 1T′′, and 1T′′′) have seen a revival of interests. Different from the edge‐sharing MoS6 trigonal prisms in the 2H MoS2 phase, these metastable phases are composed of the edge‐sharing MoS6 octahedra, in which the neighboring Mo−Mo distances differ. Due to the various crystal structures and different electronic configurations of the building MoS6 motifs, these metastable polytypes are endowed with intriguing physical properties and potential applications in diverse fields. In this Review, the recent research progress on metastable MoS2 is summarized, especially with an emphasis on the diverse synthetic approaches and the newly uncovered physical properties. The phase structures and electronic band structures are also outlined. In the end, a perspective of the future investigation on metastable MoS2 is discussed.
S‐Mo‐S three atomic layers with different Mo−S coordination and Mo−Mo bonding result in diverse polymorphs of MoS2 monolayer, the stacking order of which determines the various polytypes of bulk MoS2 crystals. In this Review, the recent research progress on metastable MoS2 is summarized, with an emphasis on the diverse synthetic approaches and the newly uncovered physical properties.
Abstract
Active electronic states in transition metal dichalcogenides are able to prompt hydrogen evolution by improving hydrogen absorption. However, the development of thermodynamically stable ...hexagonal 2H-MoS
2
as hydrogen evolution catalyst is likely to be shadowed by its limited active electronic state. Herein, the charge self-regulation effect mediated by tuning Mo−Mo bonds and S vacancies is revealed in metastable trigonal MoS
2
(1T'''-MoS
2
) structure, which is favarable for the generation of active electronic states to boost the hydrogen evolution reaction activity. The optimal 1T'''-MoS
2
sample exhibits a low overpotential of 158 mV at 10 mA cm
−2
and a Tafel slope of 74.5 mV dec
−1
in acidic conditions, which are far exceeding the 2H-MoS
2
counterpart (369 mV and 137 mV dec
−1
). Theoretical modeling indicates that the boosted performance is attributed to the formation of massive active electronic states induced by the charge self-regulation effect of Mo−Mo bonds in defective 1T'''-MoS
2
with rich S vacancies.
Ordered mesoporous carbon (OMC) is considered one of the most promising materials for electric double layer capacitors (EDLC) given its low‐cost, high specific surface area, and easily accessed ...ordered pore channels. However, pristine OMC electrode suffers from poor electrical conductivity and mechanical flexibility, whose specific capacitance and cycling stability is unsatisfactory in flexible devices. In this work, OMC is coated on the surface of highly conductive three‐dimensional graphene foam, serving as both charge collector and flexible substrate. Upon further decoration with silver nanowires (Ag NWs), the novel architecture of Ag NWs/3D‐graphene foam/OMC (Ag‐GF‐OMC) exhibits exceptional electrical conductivity (up to 762 S cm−1) and mechanical robustness. The Ag‐GF‐OMC electrodes in flexible supercapacitors reach a specific capacitance as high as 213 F g−1, a value five‐fold higher than that of the pristine OMC electrode. Moreover, these flexible electrodes also exhibit excellent long‐term stability with >90% capacitance retention over 10 000 cycles, as well as high energy and power density (4.5 Wh kg−1 and 5040 W kg−1, respectively). This study provides a new procedure to enhance the device performance of OMC based supercapacitors, which is a promising candidate for the application of flexible energy storage devices.
Ordered mesoporous carbon is proposed to be directly coated on 3D graphene foam. After further coating with 1D silver nanowires, the obtained Ag NWs/3D‐graphene foam/OMC (Ag‐GF‐OMC) exhibits exceptional electrical conductivity (up to 762 S cm−1) and mechanical robustness. As a result, it can act as a new type of flexible electrode for high performance supercapacitors.
Crystal structure determines electrochemical energy storage characteristics; this is the underlying logic of material design. To date, hundreds of electrode materials have been developed to pursue ...superior performance. However, it remains a great challenge to understand the fundamental structure–performance relationship and achieve quantitative crystal structure design for efficient energy storage. In this review, we introduce the concept of crystal packing factor (PF), which can quantify crystal packing density. We then present and classify the typical crystal structures of attractive cathode/anode materials. Comparative PF analyses of different materials, including polymorphs, isomorphs, and others, are performed to clarify the influence of crystal packing density on energy storage performance through electronic and ionic conductivities. Notably, the practical electronic/ionic conductivities of energy storage materials are based on their intrinsic characteristics related to the PF yet are also affected by extrinsic factors. The PF provides a novel avenue for understanding the electrochemical performance of pristine materials and may offer guidance on designing better materials. Additional approaches involve size regulation, doping, carbon additives, and other methods. We also propose extended PF concepts to understand charge storage and transport behavior at different scales. Finally, we provide our insights on the major challenges and prospective solutions in this highly exciting field.
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•Electrochemical performance difference of various polymorphs, isomorphs, and others, are systematically summarized and reviewed.•A novel concept of crystal packing factor is proposed to quantify crystal packing density and understand fundamental structure–activity relationship on energy storage materials.•Extended packing factor concepts are proposed to understand charge storage and transport behavior of materials at macroscopic, mesoscopic, localized scales.•Perspective and challenges of designing and predicting electrode materials for high performance energy storage are discussed.
