Good Low-Temperature Properties of Nitrogen-Enriched Porous Carbon as Sulfur Hosts for High-Performance Li–S Batteries

Despite the increased attention devoted to exploring cathode construction based on various nitrogen-enriched carbon scaffolds at room temperature, the low-temperature behaviors of Li–S cathodes have yet to be studied. Herein, we demonstrate the good low-temperature electrochemical performances of nitrogen-enriched carbon/sulfur composite cathodes. Electrochemical evaluation indicates that a reversible capacity of 368 mAh g^–1 (0.5 C) over 100 cycles is achieved at −20 °C. After returning to 25 °C, a capacity of 620 mAh g^–1 (0.5 C) is achieved over 350 cycles with a low-capacity attenuation rate (0.071% per cycle) and an initial capacity of 1151 mAh g^–1 (0.1C). This positive electrochemical property was speculated to result from the good surface chemistry of the various amine groups in the nitrogen-enriched carbon materials with enhanced polysulfide immobilization

Hierarchically Porous and Nitrogen-Rich Carbon Materials Derived from Polyimide Waste for High-Performance Supercapacitor Applications

High-performance and eco-friendly carbon electrode material for supercapacitors is still a challenge for both academia and industry. In this work, polyimide waste (PI)-derived, hierarchically porous, and nitrogen-rich carbon materials were prepared by simple hydrothermal treatment and carbonization using potassium hydroxide (KOH) as an activator. The effects of KOH/preoxidized PI mass ratio and hydrothermal treatment time on the morphology, chemical and crystalline structure, and electrochemical performance were systematically investigated. Interestingly, it is noticed that hydrothermal treatment with KOH solution can promote the infiltration and destruction of preoxidized PI, thereby enhancing the activation effect and forming a hierarchically porous structure. The specific surface area (SSA) of porous carbon with hydrothermal treatment (e.g., PIC2-24h) was as high as 2593 m2 g–1, which is much larger than that of porous carbon without hydrothermal treatment (PIC2). The as-prepared PIC2-24h presented a high specific capacitance of 229 F g–1 at 1 A g–1, superb rate performance (205 F g–1 at 10 A g–1), and excellent cycle stability (94% capacity retention after 20,000 cycles at 1 A g–1), revealing that these PI-derived porous carbon materials can not only alleviate the environmental stress caused by the disposal of PI waste but also provide an ideal candidate electrode for high-performance supercapacitor applications

Light-Induced Ring-Closing Dynamics of a Hydrogen-Bonded Adduct of Benzo[1,3]oxazine in Protic Solvents

Benzo­[1,3]­oxazine, an organic optical switching compound, is known to be in an equilibrium between its closed form (OX) and its open zwitterionic form (IN). Here we report a light-induced ring-closing mechanism of a hydrogen-bonded adduct (p-IN, partially protonated open isomer of benzo­[1,3]­oxazine) based on the observations of femtosecond and nanosecond transient absorption spectra in protic solvents. Femtosecond transient measurements upon visible excitation reveal the appearance of two states having different dynamical signatures. One corresponds to a conventional intramolecular charge transfer excited state. The other one is a concerted electron–proton transfer product (d-IN, embedded solvent molecule released from p-IN). Without steric hindrance, the main molecular structure tends to be planar upon excitation, and two intermediates, IN and OX, are involved in the sequential thermal transformation before the return to the ground state of p-IN. Specifically, in alcoholic solvents, d-IN converts to the original p-IN compound within 1 ms via the dominant pathway d-IN → IN → OX → p-IN and the side pathway d-IN → IN → p-IN, which is found to be feasible in energy; in contrast, in aqueous solution with increasing strength of intermolecular hydrogen bonding, the rate of the thermal transformation is enhanced by 1 order of magnitude

Dynamic Behavior of Molecular Switches in Crystal under Pressure and Its Reflection on Tactile Sensing

Molecular switches have attracted increasing interest in the past decades, due to their broad applications in data storage, optical gating, smart windows, and so on. However, up till now, most of the molecular switches are operated in solutions or polymer blends with the stimuli of light, heat, and electric fields. Herein, we demonstrate the first pressure-controllable molecular switch of a benzo­[1,3]­oxazine <b>OX-1</b> in crystal. Distinct from the light-triggered tautomerization between two optical states, applying hydrostatic pressure on the <b>OX-1</b> crystal results in large-scale and continuous states across the whole visible light range (from ∼430 to ∼700 nm), which has not been achieved with other stimuli. Based on detailed and systematic control experiments and theoretical calculation, the preliminary requirements and mechanism of pressure-dependent tautomerization are fully discussed. The contributions of molecular tautomerization to the large-scale optical modulation are also stressed. Finally, the importance of studying pressure-responsive materials on understanding tactile sensing is also discussed and a possible mechanotransduction mode is proposed

Dynamic Behavior of Molecular Switches in Crystal under Pressure and Its Reflection on Tactile Sensing

Molecular switches have attracted increasing interest in the past decades, due to their broad applications in data storage, optical gating, smart windows, and so on. However, up till now, most of the molecular switches are operated in solutions or polymer blends with the stimuli of light, heat, and electric fields. Herein, we demonstrate the first pressure-controllable molecular switch of a benzo­[1,3]­oxazine <b>OX-1</b> in crystal. Distinct from the light-triggered tautomerization between two optical states, applying hydrostatic pressure on the <b>OX-1</b> crystal results in large-scale and continuous states across the whole visible light range (from ∼430 to ∼700 nm), which has not been achieved with other stimuli. Based on detailed and systematic control experiments and theoretical calculation, the preliminary requirements and mechanism of pressure-dependent tautomerization are fully discussed. The contributions of molecular tautomerization to the large-scale optical modulation are also stressed. Finally, the importance of studying pressure-responsive materials on understanding tactile sensing is also discussed and a possible mechanotransduction mode is proposed

Dynamic Behavior of Molecular Switches in Crystal under Pressure and Its Reflection on Tactile Sensing

Molecular switches have attracted increasing interest in the past decades, due to their broad applications in data storage, optical gating, smart windows, and so on. However, up till now, most of the molecular switches are operated in solutions or polymer blends with the stimuli of light, heat, and electric fields. Herein, we demonstrate the first pressure-controllable molecular switch of a benzo­[1,3]­oxazine <b>OX-1</b> in crystal. Distinct from the light-triggered tautomerization between two optical states, applying hydrostatic pressure on the <b>OX-1</b> crystal results in large-scale and continuous states across the whole visible light range (from ∼430 to ∼700 nm), which has not been achieved with other stimuli. Based on detailed and systematic control experiments and theoretical calculation, the preliminary requirements and mechanism of pressure-dependent tautomerization are fully discussed. The contributions of molecular tautomerization to the large-scale optical modulation are also stressed. Finally, the importance of studying pressure-responsive materials on understanding tactile sensing is also discussed and a possible mechanotransduction mode is proposed