Ion Charge Transfer Research Articles

Gold nanoparticles−supported Ti3C2 MXene nanosheets for enhanced electrocatalytic hydrogen evolution reaction

The hydrogen evolution reaction (HER) is being widely researched and developed because it is a favorable alternative to fossil fuels to produce renewable energy. The prominent development in HER is to construct an efficient electrocatalyst aside from Pt-based catalysts, with low economic cost. In this study, gold nanoparticles (Au NPs) supported MXene (Ti3C2Tx) was designed to enhance the performance of a HER electrocatalyst. The preparation of Au NPs-supported MXene was confirmed by XRD, FTIR, Raman spectroscopy, and UV-Vis DRS. The addition of Au NPs in the MXene structure is believed to improve its catalytic performance in the hydrogen evolution reaction. The catalytic performance data of Au/MXene exhibits a better result than non-modified MXene, with a lower overpotential (179.9 mV), onset potential (87.6 mV), Tafel slope (91 mV/dec), and a higher ECSA value (54 cm2), with excellent electrocatalyst stability after ten hours of reaction time. Furthermore, the Tafel slope data of Au/MXene indicated the reaction was using the Volmer-Heyrovsky path, with the rate-determining stage being that of the Heyrovsky mechanism. The increased activity as an electrocatalyst in HER was assigned to the synergetic effect between Au nanoparticles and MXene structures, which results in high-conductivity materials with enhanced ion diffusion and charge transfer.

Biomass-based 3D micro-meso-macroporous carbon for hybrid-capacitance characteristics and incredible energy density: Reversible charge transfer of multivalent Mn ions

To achieve the coordination of energy density and power density, the metal oxide (MnO2) that endow pseudo-capacitance in 3D porous carbon can build high energy density and specific capacitance at high-power density. Here we have showed the synthetization of a composites (JSPCC-MnO2) with a specific capacitance of 310.6 F/g, an energy density of 42.4 Wh/kg, and a power density of 1425 W/kg. The percentage of pseudo-capacitance caused by the element Mn is 31.17 %, the pseudo-capacitance process of the JSPCC-MnO2 has involved reversible charge transfer from Mn (II) to Mn (IV) to achieve high specific capacitance and energy density via multiple charge transfer dynamics. And the 3D micro-meso-macro porous structure has provided the electrolyte sufficient active sites and smooth ion migration channels. Atomic-scale information has been provided by classical molecular dynamics. In polarized states, the non-polar water molecular layer is at a higher energy level, and the electrostatic adsorption force between carbon atom and K ion is higher than the hydrophobic force of carbon. The loading MnO2 has disturbed the density distribution in the local region, changed the ordered structure, and made the loading sites form defects. Green, affordable and renewable biomass has been used as the precursor achieving the high energy density of the carbon-based electrode.

A high performance TiO2 anode modified by germanium and oxygen vacancies for lithium-ion batteries

A TiO2 anode modified by germanium and oxygen vacancies was fabricated using a hydrothermal method with an autoclave at 180 °C, followed by reduction sintering at 600 °C for 5 h in a reducing atmosphere. Germanium was obtained and distributed uniformly on the surface of the anatase TiO2 particles. Oxygen vacancies were identified on the TiO2 surface by electron paramagnetic resonance and X-ray photoelectron spectroscopy. The specific capacity of the Ge@TiO2−x anode was 510 mAh g−1 after 550 charge-discharge cycles. The charge transfer and electrolyte impedance of Ge@TiO2−x were smaller than those of the initial TiO2. The lithium-ion diffusion coefficient in Ge@TiO2−x was 7.87 × 10−13 cm2·s−1, which was significantly higher than that of a commercial TiO2 anode. The germanium and oxygen vacancies in TiO2 provided more active sites for the transport of lithium ions and electrons, thereby reducing the energy barrier, accelerating the charge transfer of lithium ions and enhancing the conductivity and capacity of the Ge@TiO2−x anode.

Impacts of Mn Content and Mass Loading on the Performance of Flexible Asymmetric Solid-State Supercapacitors Using Mixed-Phase MnO2/N-Containing Graphene Composites as Cathode Materials

MnO2/nitrogen-containing graphene (x-NGM) composites with varying contents of Mn were used as the electrode materials for flexible asymmetric solid-state supercapacitors. The MnO2 was a two-phase mixture of γ- and α-MnO2. The combination of nitrogen-containing graphene and MnO2 improved reversible Faraday reactions and charge transfer. However, excessive MnO2 reduced conductivity, hindering ion diffusion and charge transfer. Overloading the electrode with active materials also negatively affected conductivity. Both the mass loading and MnO2 content were crucial to electrochemical performance. x-NGM composites served as cathode materials, while graphene acted as the anode material. Operating by two charge storage mechanisms enabled a synergistic effect, resulting in better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 exhibited the highest conductivity, efficient charge transfer, and superior capacitive characteristics. It showed a superior specific capacitance of 579 F·g−1, leading to high energy density and power density. Flexible solid-state supercapacitors using x-NGM composites demonstrated good cycle stability, with a high capacitance retention rate of 86.7% after 2000 bending cycles.

Electric-Field-Induced Assembly of an Ionic Liquid-Water Interphase Enables Efficient Heavy Metal Electrosorption.

Controlling ion desolvation, transport, and charge transfer at the electrode-electrolyte interface (EEI) is critical to enable the rational design of the efficient and selective separation of targeted heavy metals and the decontamination of industrial wastewater. The main challenge is to sufficiently resolve and interrogate the desolvation of solvated metal ions and their subsequent electroreduction at the EEI and establish pathways to modulate these intermediate steps to achieve efficient energy transfer for targeted reactive separations. Herein, we obtained a predictive understanding of modulating the desolvation and electrosorption of Pb2+ cations using the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium chloride (EMIMCl) in aqueous electrolyte. We revealed the formation of a compact interphase layer consisting of EMIMCl-Pb complexes under an applied electric field using operando electrochemical Raman spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy measurements combined with classical molecular dynamics simulations. A lower negative potential was shown to result in the formation of a well-oriented layer with the positive imidazolium ring of EMIMCl lying perpendicular to the electrode and the hydrophobic alkyl chain extending into the bulk electrolyte. This oriented layer, which formed from a dilute concentration of EMIMCl added to the electrolyte, was demonstrated to facilitate desolvation of incoming solvated Pb2+ cations and decrease the charge transfer resistance for Pb electrodeposition, which has important implications for the selective removal of Pb from contaminated mixtures. Overall, our findings open up new opportunities to modulate ion desolvation using hydrophobic ionic liquids in aqueous electrolytes for efficient heavy-metal separation.

Conveniently Revealing Lithium-Ion Battery Reaction Kinetics Using Nonlinear Frequency Response Analysis

Nonlinear Frequency Response Analysis (NFRA) can be considered a nonlinear modification of galvanostatic EIS. Due to an increased AC excitation, higher harmonics are additionally present in the voltage response of the cell [1]. Here, a single particle model (SPM) [2] in the frequency domain is used for the simulation of the NFR of lithium-ion batteries (LiB). The time-dependent processes (double-layer charging, solid diffusion) are linear in currently available SPMs. Hence, they can be described algebraically as impedances in the frequency domain. From the nonlinear, time-independent equations (Butler-Volmer, Nernst), for the case of sinusoidal excitations, a system of algebraic equations for the fundamental and higher harmonics up to a freely selectable order N is derived. By combining these systems with the impedances, we obtain a still nonlinear SPM in the frequency domain, which can be solved in a purely algebraic way for the higher harmonics. The proposed model enables researchers to conveniently analyze the NFR of LiBs. This is especially beneficial for investigations of the reaction kinetics since charge transfer coefficients can be obtained directly by parameterizing the model with NFR measurements.The abilities of the model are shown with two exemplary cell setups. At first, a symmetric cell built from metallic lithium is analyzed. The measured impedance is used to parameterize a simple equivalent circuit model (ECM), including transport through the solid electrolyte interphase (SEI). The resulting exchange current densities are used within the frequency domain SPM, which represents a nonlinear version of the ECM. Subsequently, the charge transfer coefficients of the plating/stripping reaction can be obtained conveniently by comparing the NFR measurements with the SPM response. Since the sum of obtained charge transfer coefficients is smaller than one, they are interpreted in the sense of Marcus-Hush-Chidsey kinetics [3], which is possible within a certain range of overpotential. This leads to a distinct value for the solvent reorganization energy. The calculated value is in coincidence with literature values, which are relying on high scan rate CVs with ultramicroelectrodes [4].Secondly, a full pouch cell (NMC622/Graphite) was analyzed in a similar manner. Even though the SPM cannot capture microstructural effects of the porous electrode, a sufficient fit for the EIS measurement was found. After a subsequent parameterization of the charge transfer coefficients, the NFR measurement and simulation again agree well. The resulting values for intercalation reorganization energies at the graphite anode and NMC cathode are even lower than for the plating/stripping reaction. The reorganization energies could not be validated due to the lack of literature values. However, available values for LFP [5] and a value based on unpublished data for graphite [6], are also lower compared to the plating/stripping reaction.The proposed method is very promising since it can directly capture the complete nonlinear kinetics of an electrode. Due to the frequency dependence of LiBs, the separation of kinetic and diffusive effects remains as convenient as it is for EIS.If reorganization energies are considered as given, two persistent challenges in EIS analysis could be tackled: The separation of SEI resistance and charge transfer resistance since the latter is considered as nonlinear. In addition, the ionic transport resistance and charge transfer resistance could be separated for the same reason.In the future, microstructural effects should be integrated into the model. Vidaković-Koch, T.; Miličić, T.; Živković, L. A.; Chan, H. S.; Krewer, U.; Petkovska, M. Nonlinear Frequency Response Analysis: A Recent Review and Perspectives. Opin. Electrochem. 2021, 30, 100851. https://doi.org/10.1016/J.COELEC.2021.100851.Ning, G.; Popov, B. N. Cycle Life Modeling of Lithium-Ion Batteries. Electrochem. Soc. 2004, 151 (10), A1584. https://doi.org/10.1149/1.1787631/XML.Henstridge, M. C.; Laborda, E.; Rees, N. V.; Compton, R. G. Marcus–Hush–Chidsey Theory of Electron Transfer Applied to Voltammetry: A Review. Acta 2012, 84, 12–20. https://doi.org/10.1016/J.ELECTACTA.2011.10.026.Boyle, D. T.; Kong, X.; Pei, A.; Rudnicki, P. E.; Shi, F.; Huang, W.; Bao, Z.; Qin, J.; Cui, Y. Transient Voltammetry with Ultramicroelectrodes Reveals the Electron Transfer Kinetics of Lithium Metal Anodes. ACS Energy Lett. 2020, 5 (3), 701–709. https://doi.org/10.1021/acsenergylett.0c00031.Bai, P.; Bazant, M. Z. Charge Transfer Kinetics at the Solid-Solid Interface in Porous Electrodes. Commun. 2014, 5 (1), 1–7. https://doi.org/10.1038/ncomms4585.Gao, T.; Han, Y.; Fraggedakis, D.; Das, S.; Zhou, T.; Yeh, C. N.; Xu, S.; Chueh, W. C.; Li, J.; Bazant, M. Z. Interplay of Lithium Intercalation and Plating on a Single Graphite Particle. Joule 2021, 5 (2), 393–414. https://doi.org/10.1016/J.JOULE.2020.12.020. Figure 1

Synthesis and electrochemical evaluation of porous carbon derived from sanitary pad waste for high performance in symmetric supercapacitor application

In recent years, the renewable energy storage system has attracted considerable attention from both industry and academia to address the ongoing global climate change. The waste derived porous materials gained attention as excellent electrode materials due to large specific area, good electrical conductivity to enhance ion transport and charge transfer. In this study, waste sanitary pad biomass has been successfully converted into carbon material through one-step simultaneous carbonization and activation by KOH. The as-prepared activated carbon at various temperatures was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray spectroscopy (XRD), scanning electron microscopy (SEM), Raman spectroscopy and Brunauer-Emmett-Teller (BET) techniques. The prepared biomass derived activated carbon (SWAC 800) electrode, with a large surface area of 396.1 m2g−1 delivered high specific capacitance of 306 Fg−1 at 1 Ag−1 with excellent cyclic stability in a 6 M KOH aqueous electrolyte. The electrochemical performance of the SWAC 800 electrode in a symmetric supercapacitor was evaluated in 6 M KOH and 1 M Na2SO4 electrolytes. The neutral Na2SO4 electrolyte assist SWAC 800 symmetric supercapacitor device produce excellent energy density of 32.7 Wh.kg−1 in 1.6 V operating potential window. Overall the SWAC from renewable biowaste is prospective candidate for high performance electrode material for supercapacitor application.

Field-assisted conductive substrate sparks the redox kinetics of Co9S8 in Li- and Na-ion batteries

As a promising candidate electrode material in both Li- and Na-ion batteries (L/SIBs), the application of Co9S8 is being hindered by its unsatisfactory electrochemical performance caused by the sluggish ion diffusion kinetics and drastic volume expansion. Herein, a hybrid material composed of Co9S8−x, N-doped carbon foam that seeded with Co nanoparticles (Co9S8−x@Co-NC) is constructed. Particularly, theoretical and experimental results imply that a built-in electric field at the interface of Co and NC is observed due to the variation of Fermi levels, forming rich Mott-Schottky-like heterointerfaces, which can significantly enhance the charge transfer capability between the active materials of Co9S8 and conductive NC skeleton. Moreover, the sulfur defects in Co9S8−x can not only effectively lower the energy barrier of the ion diffusion and charge transfer processes, but also endow the target sample with more storage/adsorption/active sites for Li+/Na+ ions, thus improving the rate performance of the Co9S8−x@Co-NC composite. As a result, the Co9S8−x@Co-NC exhibits fast surface-controlled redox kinetics and robust cycling stability. For instance, the Co9S8−x@Co-NC displays impressive Li-storage properties in both half and full cells with a high reversible capacity of 1007.4 mA h g−1 at 0.1 A g−1 after 100 cycles and superior rate capability up to 5 A g−1. Moreover, based on these comprehensive merits, the Co9S8−x@Co-NC composite shows decent electrochemical performance (472.2 and 311.1 mA h g−1 at 0.1 and 10 A g−1, respectively) as an anode for SIBs. This work presents an effective strategy for the construction of Mott-Schottky-like heterointerfaces in Co9S8 based materials and provides specific inspiration for future works designing high-performance electrodes via interfacial engineering.

Understanding the mechanism of performance difference when substituting Al for different transition metal ions in Li-rich Mn-based cathode materials

The Al-doped modification strategy by substituting Al for different transition metal ions (TMs, TM = Mn, Ni, Co) has achieved excellent results in improving the cyclic performance of Li-rich Mn-based cathode materials (LRMs). However, the traditional explanation known as “pegging effect” is hard to distinguish how Al works in different TM substitutions. Herein, the electrochemical performances of Li1.2Mn0.52Ni0.13Co0.13Al0.02O2 (LRM-Mn), Li1.2Mn0.54Ni0.11Co0.13Al0.02O2 (LRM-Ni) and Li1.2Mn0.54Ni0.13Co0.11Al0.02O2 (LRM-Co) are studied, and LRM-Mn shows the superior long-term cycling stability, especially at the high temperature of 55 °C. Density functional theory (DFT) reveals that LRM-Mn crystal structure has higher thermodynamic stability than any other sample, which is advantageous for inhibiting the transition of LRMs to low-energy stable phases during cycling (e.g., spinel phase and rock salt phase). Combined with density of states and Bader charge analyses, we think that the increased thermodynamic stability of LRM-Mn results from the reduction of the charge transfer of Mn and Co ions in a single delithiation process, which lowers the reactivity of TMs, alleviates the Li/TM mixing and inhibits the irreversible oxygen release. In addition, the biggest volume change during the delithiation process was observed when Al was substituted for Co, which results in the materials’ premature production of fatigue stresses and intergranular cracking. This work comprehensively explains the modification mechanism of Al-doped in LRMs. It demonstrates practical significance for both the rational design of materials and the electrode electrochemical performance prediction.

Charge-state effects on charge transfer of helium ions in gold nanosheet

We investigate the charge-state effects on charge transfer of helium ions in gold nanosheet using the time-dependent density functional theory non-adiabatically coupled to the molecular dynamics. In order to characterize and extract the charge-state information of incident particles inside the nanosheet, we develop two novel computational methods. It is found that the charge transfer behavior of He ion in gold nanosheet is sensitive to its charge state at the time of incident. Analysis of these results allows us to gain new insights in the interaction between He ions and gold nanosheet. This work validates the ability of current methodology in dealing with ion collisions in materials.

The Coordination of Titanium Ions and the Electrocrystallization Mechanism in Molten Chloride-Fluoride Salts

In electrochemical process, electrolyte composition is one of the key factors that determine the electrochemical behavior of elements. In this work, the nucleation mechanism and deposition process of titanium ions after the introduction of fluoride ions into molten salt were analyzed in detail by electrochemical technology, and the coordination behavior between fluorine ions and titanium was explored by molecular dynamics simulation, revealing the relationship between the electrocrystallization mechanism of titanium and its coordination properties. It can be found that the electrocrystallization mechanism of titanium ions is related to its coordination structure. Under our experimental conditions, the Ti-Cl bond in the system was gradually replaced by the Ti-F bond. This will lead to the change of charge transfer and ion diffusion of titanium ions, which will have an important effect on the electrocrystallization processes. This work has an important guiding significance for further study on the influence of different molten salt systems on the electrocrystallization mechanism of molten salt electrolytic titanium.

Carbon Nanosheets-Based Supercapacitor Materials: Recent Advances and Prospects.

The need for inexpensive and ecologically sustainable energy storage technologies is rising rapidly along with the severity of the world's environmental challenges as well as with the rising demand for portable electronics and hybrid vehicles. Supercapacitors have drawn a lot of attentions lately in this regard because of their ultrahigh power density, outstanding electrochemical stability, and environmental friendliness. Due to various advantages, carbon materials are the choice of designer for developing commercial electrodes for various applications including devising supercapacitors. Two-dimensional (2D) carbon nanosheets (CNSs) with a large surface area and excellent electronic transport properties have fired up the interest of researchers due to their unique properties and potential applications in energy storage. Such engineered 2D porous CNS may significantly improve the energy storage performance of supercapacitor by enabling fast ion transport and charge transfer kinetics. This article summarizes the most recent and significant advances in the area of activated, porous, graphene-based various CNSs and their composites with a special focus on their use as supercapacitor electrodes. A succinct overview about their syntheses and key characterizations regarding their different structural aspects have been discussed. The present challenges and prospects in using CNS in supercapacitor applications are highlighted.

Long-term stability electrochromic electrodes based on porous tungsten trioxide and nickel oxide films via a facile triple pulse electrodeposition

Herein, a facile triple pulse electrodeposition was used to fabricate porous films such as tungsten trioxide (WO3) and nickel oxide (NiO) on indium tin oxide (ITO) substrates. These porous films outperformed corresponding compact films formed by continuous electrodeposition in terms of long-term stability. The maximum transmittance modulation of P-WO3 and P–NiO films were 57.0% and 52.1%, respectively, and changed insignificantly after 10,000 cycles, whereas C-WO3 and C–NiO films were degraded after 2500 and 1000 cycles, respectively. Not only does the porous morphology increases the electrochemical active surface area, but it also provides an efficient pathway for ion diffusion and charge transfer, resulting in fast kinetics, low resistance, high electro-activity, and excellent ion reversibility. This work will hopefully inspire more researchers to improve electrodeposition film fabrication and promote electrochromic device industrialization.

Thermally Driven Multilevel Non-Volatile Memory with Monolayer MoS2 for Brain-Inspired Artificial Learning.

The demands of modern electronic components require advanced computing platforms for efficient information processing to realize in-memory operations with a high density of data storage capabilities toward developing alternatives to von Neumann architectures. Herein, we demonstrate the multifunctionality of monolayer MoS2 memtransistors, which can be used as a high-geared intrinsic transistor at room temperature; however, at a high temperature (>350 K), they exhibit synaptic multilevel memory operations. The temperature-dependent memory mechanism is governed by interfacial physics, which solely depends on the gate field modulated ion dynamics and charge transfer at the MoS2/dielectric interface. We have proposed a non-volatile memory application using a single Field Effect Transistor (FET) device where thermal energy can be ventured to aid the memory functions with multilevel (3-bit) storage capabilities. Furthermore, our devices exhibit linear and symmetry in conductance weight updates when subjected to electrical potentiation and depression. This feature has enabled us to attain a high classification accuracy while training and testing the Modified National Institute of Standards and Technology datasets through artificial neural network simulation. This work paves the way toward reliable data processing and storage using 2D semiconductors with high-packing density arrays for brain-inspired artificial learning.

Enhanced rate and specific capacity in nanorod-like core-shell crystalline NiMoO4@amorphous cobalt boride materials enabled by Mott-Schottky heterostructure as positive electrode for hybrid supercapacitors

The supercapacitor electrode materials suffer from structure pulverization and sluggish electrode kinetics under high current rates. Herein, a unique NiMoO4@Co-B heterostructure composed of highly conductive Co-B nanoflakes and a semiconductive NiMoO4 nanorod is designed as an electrode material to exert the energy storage effect on supercapacitors. The formed Mott-Schottky heterostructure is helpful to overcome the ion diffusion barrier and charge transfer resistance during charging and discharging. Moreover, this crystalline-amorphous heterogeneous phase could provide additional ion storage sites and better strain adaptability. Remarkably, the optimized NiMoO4@Co-B hierarchical nanorods (the mass ratio of NiMoO4/Co-B is 3:1) present greatly enhanced electrochemical characteristics compared with other components, and show superior specific capacity of 236.2 mA h g−1 at the current density of 0.5 A g−1, as well as remarked rate capability. The present work broadens the horizons of advanced electrode design with distinct heterogeneous interface in other energy storage and conversion field.

Mechanochemistry toward Organic "Salt" via Integer-Charge-Transfer Cocrystal Strategy for Rapid, Efficient, and Scalable Near-Infrared Photothermal Conversion.

Inspired by the concept of ionic charge-transfer complexes for the Mott insulator, integer-charge-transfer (integer-CT) cocrystals are designed for NIR photo-thermal conversion (PTC). With amino-styryl-pyridinium dyes and F4TCNQ (7,7',8,8'-Tetracyano-2,3,5,6-tetrafluoroquinodimethane) serving as donor/acceptor (D/A) units, integer-CT cocrystals, including amorphous stacking "salt" and segregated stacking "ionic crystal", are synthesized by mechanochemistry and solution method, respectively. Surprisingly, the integer-CT cocrystals are self-assembled only through multiple D-A hydrogen bonds (C-H⋅⋅⋅X (X=N, F)). Strong charge-transfer interactions in cocrystals contribute to the strong light-harvesting ability at 200-1500 nm. Under 808 nm laser illumination, both the "salt" and "ionic crystal" display excellent PTC efficiency beneficial from ultrafast (∼2 ps) nonradiative decay of excited states. Thus integer-CT cocrystals are potential candidates for rapid, efficient, and scalable PTC platforms. Especially amorphous "salt" with good photo/thermal stability is highly desirable in practical large-scale solar-harvesting/conversion applications in water environment. This work verifies the validity of the integer-CT cocrystal strategy, and charts a promising path to synthesize amorphous PTC materials by mechanochemical method in one-step.

A Comparative Study on Gemological Characteristics and Color Formation Mechanism of Moqi Agate, Inner Mongolia Province, China

Agate attracts the attention of gem mineralogists because of its variable colors. The color of agate is closely related to its naming and classification, so it is necessary to study the color and mineral origin of agate. In this paper, the mineralogical characteristics and color origin of red, yellow and green Moqi agates from Inner Mongolia were systematically studied by means of Fourier transform infrared spectrometer, Raman spectrometer, X-ray powder diffractometer, electron probe microanalyzer and ultraviolet–visible spectrophotometer. It is found that the color of Moqi agate is related to the minerals and trace elements contained in it, and is associated with the electron transition or charge transfer of Fe ions in the contained minerals. Green agate has the highest Fe content, and its color is caused by celadonite inclusions. The red and yellow color in Moqi agate is mainly caused by hematite and goethite, while red agate contains more Fe than yellow agate. Raman spectroscopy and X-ray diffraction analysis show that the content of moganite in Moqi agate is 0–30%. It is calculated that the crystallinity of Moqi agate is 1.5–3.5. This work provides a theoretical basis for future research on the identification of Moqi agate.

Preparation and Characterization of Asphalt Pitch-Derived Activated Carbons with Enhanced Electrochemical Performance as EDLC Electrode Materials

This study used a physical activation method to prepare asphalt-pitch-derived activated carbon (Pitch AC) for an electric double-layer capacitor (EDLC) electrode. X-ray diffraction analysis and Raman spectroscopy were used to estimate the change in the crystal structure of Pitch AC with activation time. In addition, the textural properties of Pitch AC were studied by Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR) and non-localized density functional theory (NLDFT) equations with N2/77K isotherm adsorption-desorption curves. The electrochemical performance of the Pitch AC was analyzed using a coin-type EDLC with 1 M SBPBF4/PC via galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area and total pore volume were 990–2040 m2/g and 0.42–1.51 cm3/g, respectively. The pore characteristics of the Pitch AC varied according to the activation time and changed from a microporous structure to a micro-mesoporous structure as the activation time increased. The electrochemical performance analysis also found that the specific capacity was increased from 43.6 F/g to 84.5 F/g at 0.1 A/g as activation time increased. In particular, Pitch AC-9 exhibited the best electrochemical performance (rectangular CV curve, reversible GCD, lowest ion charge transfer resistance and Warburg impedance). In addition, Pitch AC-9 was confirmed to have a specific capacitance similar to commercial activated carbon for EDLC (YP-50F). Therefore, it was considered that Pitch AC could replace commercial activated carbon for EDLC because it has excellent pore characteristics and electrochemical performance despite being manufactured through a very low-cost precursor and a simple process (physical activation method).

A robust strategy for crafting LiTiOPO4/CeO2 composites towards high rate lithium ion battery

LiTiOPO4/CeO2 composites as high-performance anodes for lithium-ion batteries (LIBs) were synthesized by a simple hydrothermal and high-temperature solid-phase method. X-ray diffraction (XRD) analysis results showed that CeO2-motified LiTiOPO4 was successfully prepared. Electron microscopy observation of the structural and morphological analysis data of the prepared materials further showed that CeO2 was coated on the surface of LiTiOPO4. X-ray photoelectron spectroscopy (XPS) showed different valence states of Ce4+/Ce3+ exist in LiTiOPO4/CeO2. The Ce3+-doped LiTiOPO4 with CeO2 surface modification was used to enhance lithium-ion storage performance by mediating voltage from 0.01 to 3.0 V. The rate capacity of the LiTiOPO4/CeO2 was maintained at 295.5 mAh g−1. The specific discharge capacity was maintained at 206.5 mAh g−1 after 1000 cycles, at 5 A g−1. The CeO2 not only significantly enhances ion diffusion and charge transfer, but also reduces polarization, promotes transport of Li+ to more storage sites in LiTiOPO4.

High-efficiency and selective removal of Hg(Ⅱ) and Pb(Ⅱ) ions from aquatic system by 1T/2H mixed-phase MoSe2 nanoflowers: Performance and mechanism

High-efficiency and selective removal of heavy metal ions from aquatic system is urgently needed and remains a major challenge. Endowed with rich Se atoms and unique 2D structure, MoSe2 should be promising for the removal of heavy metal ions. However, it remains challenging to balance the efficient exposure of active sites and the stability of materials, and the potential mechanism of the interactions between heavy metal ions and the interface of MoSe2 with different crystal phases and structures has yet to be comprehensively explored. Herein, mixed-phase 1T/2H MoSe2 nanoflowers featured with ultrathin nanosheets, high ratio of 1T phase, enlarged interlayer spacing, and defect-rich structure have been synthesized and demonstrated excellent performance for removing Hg(II) and Pb(II) ions from aquatic system, including high capacity (952.4 mg·g−1 for Hg(II); 217.9 mg·g−1 for Pb(II)), rapid kinetics, superior selectivity, and anti-interference ability. The ultrathin nanosheets and enlarged interlayer spacing ensured efficient exposure of Se atoms; the high ratio of 1T phase was beneficial for the binding of heavy metal ions (as confirmed by DFT calculations). The defect-rich structure not only provided additional channels for ions diffusion, but also produced more active sites for ion binding and charge transfer. Benefiting from these structural characteristics, 1T/2H MoSe2 could effectively and selectively remove Hg(II) and Pb(II) ions under the coexistence of various cations in practical water environment, the corresponding separation factors were greater than 170. Moreover, the interaction mechanism between two target ions and MoSe2 was elucidated byexperimentandDFT calculation. The present work not only explored advanced materials for the purification of heavy metal ions polluted water, but also may promote the exploration of MoSe2 in environmental remediation.