Defect engineering (doping and vacancy) has emerged as a positive strategy to boost the intrinsic electrochemical reactivity and structural stability of MnO2‐based cathodes of rechargeable aqueous ...zinc ion batteries (RAZIBs). Currently, there is no report on the nonmetal element doped MnO2 cathode with concomitant oxygen vacancies, because of its low thermal stability with easy phase transformation from MnO2 to Mn3O4 (≥300 °C). Herein, for the first time, novel N‐doped MnO2–x (N‐MnO2–x) branch arrays with abundant oxygen vacancies fabricated by a facile low‐temperature (200 °C) NH3 treatment technology are reported. Meanwhile, to further enhance the high‐rate capability, highly conductive TiC/C nanorods are used as the core support for a N‐MnO2–x branch, forming high‐quality N‐MnO2–x@TiC/C core/branch arrays. The introduced N dopants and oxygen vacancies in MnO2 are demonstrated by synchrotron radiation technology. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N‐MnO2–x@TiC/C arrays are endowed with faster reaction kinetics, higher capacity (285 mAh g−1 at 0.2 A g−1) and better long‐term cycles (85.7% retention after 1000 cycles at 1 A g−1) than other MnO2‐based counterparts (55.6%). The low‐temperature defect engineering sheds light on construction of advanced cathodes for aqueous RAZIBs.
With a facile hydrothermal process and subsequent low‐temperature (200 °C) NH3 treatment, N‐doped MnO2–x (N‐MnO2–x) branch arrays with concomitant oxygen vacancies are fabricated on conductive TiC/C backbones to form N‐MnO2–x@TiC/C core/branch arrays. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N‐MnO2–x@TiC/C arrays cathode exhibits excellent electrochemical performance in zinc ion batteries.
Identifying factors for the prediction of depression is a long‐standing research topic in psychiatry and psychology. Perceived stress, which reflects the tendency to appraise one's life situations as ...stressful and overwhelming, has emerged as a stable predictor for depressive symptoms. However, the neurobiological bases of perceived stress and how perceived stress influences depressive symptoms in the healthy brain remain largely unknown. Here, we investigated these issues in 217 healthy adolescents by estimating the fractional amplitude of low‐frequency fluctuations (fALFFs) via resting‐state functional magnetic resonance imaging. A whole‐brain correlation analysis showed that higher levels of perceived stress were associated with greater fALFF in the left superior frontal gyrus (SFG), which is a core brain region for cognitive control and emotion regulation‐related processes. Mediation analysis further indicated that perceived stress mediated the link between the fALFF in the left SFG and depressive symptoms. Importantly, our results remained significant even when excluding the influences of head motion, anxiety, SFG gray matter structure, and school environment. Altogether, our findings suggested that the fALFF in the left SFG is a neurofunctional marker of perceived stress in adolescents and revealed a potential indirect effect of perceived stress on the association between the SFG spontaneous activity and depressive symptoms.
Abstract
Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency ...of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation of gradient tantalum-doped hematite homojunction nanorods by combination of hydrothermal regrowth strategy and hybrid microwave annealing, which enhances the photocurrent density and reduces the turn-on voltage simultaneously. The unusual bi-functional effects originate from the passivation of the surface states and intrinsic built-in electric field by the homojunction formation. The additional driving force provided by the field can effectively suppress charge–carrier recombination both in the bulk and on the surface of hematite, especially at lower potentials. Moreover, the synthesized homojunction shows a remarkable synergy with NiFe(OH)
x
cocatalyst with significant additional improvements of photocurrent density and cathodic shift of turn-on voltage. The work has nicely demonstrated multiple collaborative strategies of gradient doping, homojunction formation, and cocatalyst modification, and the concept could shed light on designing and constructing the efficient nanostructures of semiconductor photoelectrodes in the field of solar energy conversion.
We have provided a brief review about biomass derived carbon materials and their applications for electrochemical energy storage.
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•Provide a brief review about biomass derived carbon ...materials.•Address the pore formation mechanism on carbon materials.•Hierarchical porous carbon show high capacity and good cycles.•Demonstrate two effective pore formation methods on carbon.
Natural biomass-derived carbons have attracted great attention due to their interesting characteristics of naturally porous or hierarchical structured and heteroatom doping. In this review, the recent progress in the synthesis of naturally-derived carbon and their composite electrodes is summarized in detail. Advantages and disadvantages of different methods (e.g., chemical and physical activations) are discussed. In addition, we further address the pore formation mechanism on biomass-derived carbons. Furthermore, their applications for electrochemical energy storage in lithium ion batteries and sodium ion batteries are briefly reviewed and highlighted associated with their structural merits such as hierarchical porous structure, high conductivity as well as large surface area. Outlook of research trends on next-generation high-performance electrodes based on biomass-derived carbons is provided at the end.
Modular multilevel converter (MMC) is considered as a promising topology for voltage-source converter (VSC) high-voltage, direct current (HVDC) applications. This paper presents a new control ...strategy for MMC-HVDC under unbalanced grid conditions. First, a new inner loop current control strategy based on nonideal proportional resonant (PR) controllers in stationary αβ frame is designed, which is more concise compared to the existing dual sequence current control scheme. Second, an analytical expression for circulating current is obtained which shows that the circulating currents will be asymmetric under unbalanced grid conditions and can be decomposed into positive-, negative-, and zero-sequence component. In order to suppress all these components, a new circulating current suppressing strategy is analyzed and designed also based on nonideal PR controllers. Application of nonideal PR controllers makes the control system well adapt to the fluctuation of grid frequency. The effectiveness of the proposed control strategy is verified through a simulation case of a 251-level MMC-HVDC transmission system using real-time digital simulator.
Lithium–sulfur batteries (LSBs) are considered to be one of the most promising alternatives to the current lithium‐ion batteries (LIBs) to meet the increasing demand for energy storage owing to their ...high energy density, natural abundance, low cost, and environmental friendliness. Despite great success, LSBs still suffer from several problems, including undermined capacity arising from low utilization of sulfur, unsatisfactory rate performance and poor cycling life owing to the shuttle effect of polysulfides, and poor electrical conductivity of sulfur. Under such circumstances, the design/fabrication of porous carbon–sulfur composite cathodes is regarded as an effective solution to overcome the above problems. In this review, different synthetic methods of porous carbon hosts and their corresponding integration into carbon–sulfur cathodes are summarized. The pore formation mechanism of porous carbon hosts is also addressed. The pore size effect on electrochemical performance is highlighted and compared. The enhanced mechanism of the porous carbon host on the sulfur cathode is systematically reviewed and revealed. Finally, the combination of porous carbon hosts and high‐profile solid‐state electrolytes is demonstrated, and the challenges to realize large‐scale commercial application of porous carbon–sulfur cathodes is discussed and future trends are proposed.
Carbon and sulfur: Despite great success, lithium–sulfur batteries (LSBs) still suffer from several problems. The design/fabrication of porous carbon–sulfur composite cathodes is regarded as an effective solution to overcome problems such as poor capacity arising from low utilization of sulfur, unsatisfactory rate performance and poor cycling life owing to the shuttle effect of polysulfides, and poor electrical conductivity of sulfur. In this review, different synthetic methods for porous carbon hosts and their corresponding integration into carbon–sulfur cathodes are thus summarized.
It is of great importance to reinforce electronic and ionic conductivity of Li4Ti5O12 electrodes to achieve fast reaction kinetics and good high‐power capability. Herein, for the first time, a dual ...strategy of combing N‐doped Li4Ti5O12 (N‐LTO) with highly conductive TiC/C skeleton to realize enhanced ultrafast Li ion storage is reported. Interlinked hydrothermal‐synthesized N‐LTO nanosheets are homogeneously decorated on the chemical vapor deposition (CVD) derived TiC/C nanowires forming binder‐free N‐LTO@TiC/C core–branch arrays. Positive advantages including large surface area, strong mechanical stability, and enhanced electronic/ionic conductivity are obtained in the designed integrated arrays and rooted upon synergistic TiC/C matrix and N doping. The above appealing features can effectively boost kinetic properties throughout the N‐LTO@TiC/C electrodes to realize outstanding high‐rate capability at different working temperatures (143 mAh g−1/10 C at 25 °C and 122 mAh g−1/50 C at 50 °C) and notable cycling stability with a capacity retention of 99.3% after 10 000 cycles at 10 C. Moreover, superior high‐rate cycling life is also demonstrated for the full cells with N‐LTO@TiC/C anode and LiFePO4 cathode. The dual strategy may provoke wide interests in fast energy storage areas and motivate the further performance improvement of power‐type lithium ion batteries (LIBs).
Herein, dual “inside and outside” strategies of combing N‐doped Li4Ti5O12 (N‐LTO) with highly conductive TiC/C skeleton is reported to construct integrated N‐LTO@TiC/C core‐branch arrays for ultra‐fast Li ion storage. Positive advantages including large surface area and enhanced electronic/ionic conductivity are obtained in the designed integrated arrays, leading to outstanding high‐rate capability for N‐LTO@TiC/C electrodes.
UiO-66-(OH)2 emits yellow-green light under ultraviolet light. With adding Fe3+, fluorescence quenching occurs because of the nonradiative electron/hole recombination annihilation. Ascorbic acid (AA) ...can reduce Fe3+ to Fe2+, which destroys the electron transfer between UiO-66-(OH)2 and Fe3+, leading to the fluorescence recovery of UiO-66-(OH)2.
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In this research, a hydroxyl group functionalized metal-organic framework (MOF), UiO-66-(OH)2, was synthesized as a “on-off-on” fluorescent switching nanoprobe for highly sensitive and selective detection of Fe3+, ascorbic acid (AA) and acid phosphatase (ACP). UiO-66-(OH)2 emits yellow-green light under ultraviolet light, when Fe3+ was added, Fe3+ was chelated with hydroxyl group, the electrons in the excited state S1 of the MOF transferred to the half-filled 3d orbits of Fe3+, resulting in fluorescence quenching because of the nonradiative electron/hole recombination annihilation. AA could reduce Fe3+ to Fe2+, which can destroy the electron transfer between UiO-66-(OH)2 and Fe3+ after AA adding, resulted in nonoccurrence of the nonradiative electron transfer, leading to the recovery of UiO-66-(OH)2 fluorescence intensity. The probe can also be used to detect ACP based on the enzymolysis of 2-phospho-l-ascorbic acid (AAP) to produce AA. Benefitting from the hydroxyl group and the characteristics of UiO-66, including the high porosity and large surface area, the developed UiO-66-(OH)2 showed extensive advantages as a fluorescent probe for detection of multi-component, such as high sensitivity and selectivity, colorimetric detection, fast response kinetics and easy to operate, economical and secure. This is the first time to use active group functionalized MOFs as a multi-component sensor for these three substances detection.
The development of high‐performance dendrite‐free liquid‐metal anodes at room temperature is of great importance for the advancement of alkali metal batteries. Herein an intriguing self‐healing ...liquid dendrite‐free Na–K alloy, fabricated by a facile room‐temperature alloying process, aiming for application in potassium‐ion batteries is reported. Through extensive investigation, its self‐healing characteristics are rooted upon a thin solid K2O layer (KOL) coated on the liquid Na–K alloy. The KOL not only acts as a protective layer to prevent the Na–K alloy from making contact with the electrolyte, but also greatly improves the wetting capability and adhesion between the liquid alloy and the carbon matrix (e.g., carbon fiber cloth (CFC)) to form a stable interface. Consequently, the as‐prepared CFC/KOL@Na–K alloy anode exhibits prominent electrochemical performance with smaller hysteresis (less than 0.3 V beyond 140 cycles at 0.4 mA cm−2), better capacity retention, and higher Coulombic efficiency than the CFC/bare Na–K alloy counterpart. When coupled with a potassium Prussian blue (PPB) cathode, the full cell manifests higher capability retention and improved cycling stability. This research deepens the understanding of self‐healing Na–K alloys and opens a new way to achieve high‐performance dendrite‐free alkali metal anodes for application in rechargeable batteries.
A dendrite‐free self‐healing K2O@Na–K liquid alloy consisting of a Na–K liquid core and a solid K2O shell is prepared by a facile room‐temperature alloying process. Due to the excellent seal‐healing ability, enhanced wetting properties, and strong adhesion with a carbon fiber cloth (CFC) matrix, the designed CFC/KOL@Na–K alloy electrode exhibits noticeable electrochemical performance with smaller hysteresis, better cycling stability, and higher Coulombic efficiency.
Construction of stable dendrite‐free Li metal anode is crucial for the development of advanced Li–S and Li–air batteries. Herein, self‐supported TiC/C core/shell nanowire arrays as skeletons and ...confined hosts of molten Li forming integrated trilayer TiC/C/Li anode are described. The TiC/C core/shell nanowires with diameters of 400–500 nm exhibit merits of good lithiophilicity, high electrical conductivity, and abundant porosity. The as‐prepared TiC/C/Li anode exhibits prominent electrochemical performance with a small hysteresis of less than 85 mV beyond 200 cycles (3.0 mA cm−2) as well as a very high Coulombic efficiency up to 98.5% for 100 cycles at 1.0 mA cm−2. When the structured anode is coupled with lithium iron phosphate or sulfur cathode, the assembled full cells with trilayer TiC/C/Li anodes display enhanced capability retention and improved Coulombic efficiency. This is ascribed to the unique TiC/C matrix, which can not only provide interspace for accommodating “hostless” Li, but also afford interconnected rapid transfer paths for electrons and ions with low local current densities, leading to effective inhabitation growth of Li dendrites and lower interfacial resistance. A fresh way for construction of advanced stable Li metal anodes is provided in this work.
A unique integrated trilayer TiC/C/Li anode is constructed through rational combination of self‐supported TiC/C core/shell nanowire arrays and melt‐infusion process. Attributed to ultralow current density, stabilized solid electrolyte interphase film, and limited volume change, the TiC/C/Li anode exhibits lower hysteresis, enhanced cycling stability, and higher Coulombic efficiency.
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