Enhanced Charge Density Research Articles

Simple enhanced charge density of chitosan film by the embedded ion method for the flexible triboelectric nanogenerator

This research proposed a simple ionic embedded method to improve electrical output performance by adding surface charges of cationic chitosan (CS) biopolymer for compatible utilization of the triboelectric nanogenerator (TENG). By simply embedding cationic salts, the TENG performance was enhanced by over four times more than that with pristine CS. Moreover, by modifying roughness on the film surface, the optimized condition of R-CS/3 %CaCl2 reached the highest VOC and ISC of ~149 V and ~15 μA, respectively, thus exceeding the output from pristine R-CS TENG by four- and three times of ⁓38 V and ⁓5.1 μA. The maximum power output of 400 μW/cm2 can be observed at the 10 MΩ external load resistance. Finally, by integrating an automatic self-charge pumping (ASCP) module, the ASCP/CS-TENG provided highly efficient VOC and ISC output power by over 1.3 times more than the R-CS/3 %CaCl2 TENG and could light up 72 light emitting diodes (LEDs) easily.

Phase transition enhanced pyroelectric nanogenerators for self-powered temperature sensors

Pyroelectric materials are of interest for waste heat utilization and thermal detection. However, the low output current and inefficiency reduces their effectiveness. Here, we utilize the abrupt decrease in polarization of ferroelectric BaTiO3 materials around Curie temperature to improve the output performance of a pyroelectric nanogenerator. The variation of the polarization leads to a large change in the density of surface free charges, resulting in an increase of pyroelectric current. We have designed a temperature control and recording system to realize direct measurement of the pyroelectric output current. The pyroelectric current, power and energy conversion efficiency of the device near the Curie temperature were measured to be 15.6-fold, 18-fold and 15.8-fold higher than those acquired near room temperature. Moreover, the temperature induced current and charge density enhancement can be applied to detect temperature and temperature change. The responsivity of the self-powered temperature sensor near Tc is 120 nC/cm2∙K, which 4.8 times higher than that near room temperature (25.1 nC/cm2∙K). The results confirmed the ability to exploit a ferroelectric phase transition for pyroelectric performance enhancement.

Superhigh charge density and direct-current output in triboelectric nanogenerators via peak shifting modified charge pumping

Due to the great potentials in self-powered sensors and micro-nano power sources, triboelectric nanogenerator (TENG) has attracted numerous attentions. However, enhancing charge density and realizing direct-current (DC) are long-term significant issues for TENGs. In this work, we investigated a DC TENG with outstanding electricity generation characteristics based on quasi- synchronous double-stage self-charge pumping. The TENG works in a contact-separation mode with a four-layered parallel structure. The TENG possesses a high open-circuit voltage of 2300 V, a high short-circuit current of 3 mA, a high power of 150 mW and a superhigh transferred charge of 20 μC at 4 Hz, which are significantly enhanced from those in single-stage pumping and non pumped counterpart TENGs. The property-improving mechanism lies in that through the unidirectional self-charge pump with a slight time difference among TENGs, negative halves are moved to the adjacent positive halves, leads to the widening, higher and DC outputs at the final terminal, which employs the Plancherel theorem for peak shifting in framework of energy conservation law. The TENG can power light emitting diodes, electronic devices and an electrophoretic deposition of pigment coatings. This work provides a method for developing high-performance DC TENGs with superhigh transferred charge for various applications.

Unveiling the positive effect of mineral induced natural organic matter (NOM) on catalyst properties and catalytic dechlorination performance: An experiment and DFT study

Herein, we report the significant effects of natural organic matter contained in natural zeolite (Z-NOM) on the physicochemical characteristics of a Ni/Fe@natural zeolite (NF@NZ) catalyst and its decontamination performance toward the dechlorination of trichloroethylene (TCE). Z-NOM predominantly consists of humic-like substances and has demonstrable utility in the synthesis of bimetallic catalysts. Compared to NF@NZ600C (devoid of Z-NOM), NF@NZ had increased dispersibility and mobility and showed significant enhancement in the catalytic dechlorination of TCE owing to the encapsulation of Ni0/Fe0 nanoparticles by Z-NOM. The results of corrosion experiments, spectroscopic analyses, and H2 production experiments confirmed that Ni0 acted as an efficient cocatalyst with Fe0 to enhance the dechlorination of TCE to ethane, and Z-NOM-capped Ni0 showed improved adsorption of TCE and atomic hydrogen on their reactive sites and oxidation resistance. The density functional theory (DFT) studies have substantiated the improved adsorption of TCE due to the presence of NOM (especially by COOH structure) and the enhanced charge density at the Ni site in the Ni/Fe bimetal alloy for the stronger adsorption of hydrogen atoms that ultimately enhanced the TCE reduction reaction. These findings illustrate the efficiency of NOM containing natural minerals toward the synthesis of bimetallic catalysts for practical applications.

Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor.

Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa2Cu3O6+x after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within ≈1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.

High thermoelectric figure of merit for GeS/phosphorene 2D heterostructures: A first-principles study

2D materials, such as graphene, transition metal dichalcogenides, and black phosphorus (i.e., phosphorene), have attracted wide interest as efficient thermoelectric materials. Herein, we propose GeS/phosphorene (GeS/BP) heterostructure as a promising high-performance thermoelectric material. We have investigated the electronic structure and the thermoelectrical properties of the GeS/BP 2D system using first-principles calculations combined with the semi-classical Boltzmann transport theory. We have also addressed the effect of temperature and chemical potential on its transport properties. Our calculations revealed a high thermoelectrical figure of merit (ZT) of 2.53 for the GeS/BP system. Interestingly, ultrahigh room temperature ZT values amounting to 14.01 and 33.39 could be attained through p-type doping of the GeS/BP heterostructures. We ascribe the remarkably high ZT to the increase of the Seebeck coefficient in the system and the enhanced charge density redistribution at the GeS/BP interface. These findings highlight a promising strategy to achieve high-performance thermoelectric materials through nanostructuring of 2D materials.

Superconductivity in (Ba,K)SbO3

(Ba,K)BiO3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature Tc of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO3 with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO3. The parent compound BaSbO3−δ shows a larger charge density wave gap compared to BaBiO3. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to Tc = 15 K. This value is lower than the maximum Tc of (Ba,K)BiO3, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO3 indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.

A numerical study of effects of aerosol particles on the electric activities of a thunderstorm with a 1.5D aerosol-cloud bin model

Numerical simulations are carried out to study the effects of aerosol particles acted as cloud condensation nuclei (CCN) and ice nuclei (IN) on thunderstorm properties. A two-cylinder time-dependent cloud and aerosol interaction model with the spectral bin microphysical parameterization, explicit noninductive electrification and lightning process is utilized to explore the impacts. This model not only uses the high-resolution particle size bins to describe the distributions of aerosol particles and hydrometeors, but also can be applied to study the diffusional growth of aerosol particles to cloud droplets and to track the mass of both CCN and IN in hydrometeors. The simulated cloud properties show that increased CCN concentrations result in more numerous but smaller droplets and form ice particles less efficiently, producing less numbers of graupel and less efficient conversion to raindrops. Increased IN concentrations directly enhance the heterogeneous nucleation, and then boost the subsequent microphysical processes, contributing to the production of increasingly numbers of graupel which eventually pass through the melting layer and then enhance the precipitation. As CCN concentrations increase, the charge density gained by different mass-binned ice particles and total charge density significantly decrease due to reduced large ice particles with greater diameters than 360 μm. In contrast, as IN concentrations are further increased, dramatically increased large ice particles with greater diameters than 360 μm are produced and thus, support the enhanced charge density gained by different mass-binned ice particles and total charge density. Besides, as expected, the reduced (enhanced) lightning frequency is well explained by the reduced (increased) numbers of large ice particles (diameter>360 μm).

Evaporation-assisted phase separation preparation and electrorheological effect of poly(ionic liquid) microspheres with dual and mixed counterions

We prepare poly(ionic liquid) (PIL) microspheres containing dual counterion and single counterion in a unitary unit via an evaporation-assisted phase separation method, and study the influence of the number and type of counterions on the electrorheological (ER) effect and dielectric properties of the PIL microspheres. The morphology and structure of PIL microspheres are characterized and the ER effect of PIL microspheres in insulating carrier liquid is measured under electric fields. It shows that when the type of counterions is identical, the dual-ion PIL (D-PIL) microspheres have a stronger ER effect than that of the single-ion PIL (S-PIL) microspheres. Dielectric spectra analysis indicates that D-PIL microspheres have higher interfacial polarization rate compared to S-PIL microspheres due to enhanced charge density and ion transport dynamics according to Raman spectra and activation energy analysis. This should be responsible for the stronger ER effect of D-PIL microspheres. However, when the type of counterions is different, the ER effect of D-PIL microspheres is largely reduced. This is because the mixed alkali effect of mixed counterions significantly increases the activation energy of ion transport and decreases conductivity and interfacial polarization rate of PIL microspheres containing mixed counterions. The result can provide a new understanding of structure-property relationship for PIL-based ER material design and preparation.

Covalent Organic Framework-Mediated Thin-Film Composite Polyamide Membranes toward Precise Ion Sieving.

Covalent organic frameworks (COFs) have evinced a potential solution that promises for fast and efficient molecular separation due to the presence of orderly arranged pores and regulable pore apertures. Herein, the synthesized COF (TPB-DMTP-COF) with the pore aperture matching the pore size of the nanofiltration (NF) membrane was utilized to modulate the physicochemical characters of the polyamide (PA) membranes. It is demonstrated that COFs with superior polymer affinity and hydrophilicity not only circumvent the nonselective interfacial cavities but also improve the hydrophilicity of the resultant thin-film nanocomposite (TFN) membranes. Furthermore, the predeposited COF layer is able to slow down the diffusion rate toward the reaction boundary through hydrogen bonding, which is consistent with the results of molecular dynamic (MD) and dissipative particle dynamic (DPD) simulations. In this context, COF-modulated TFN membranes show a roughened and thickened surface with bubble-shaped structures in contrast to the nodular structure of original polyamide membranes. Combined with the introduced in-plane pores of COFs, the resultant TFN membranes display a significantly elevated water permeance of 35.7 L m2 h-1 bar-1, almost 4-fold that of unmodified polyamide membranes. Furthermore, the selectivity coefficient of Cl-/SO42- for COF-modulated TFN membranes achieves a high value of 84 mainly related to the enhanced charge density, far exceeding the traditional NF membranes. This work is considered to provide a guideline of exploring hydrophilic COFs as an interlayer for constructing highly permeable membranes with precise ion-sieving ability.

Frequency Band Broadening and Charge Density Enhancement of a Vibrational Triboelectric Nanogenerator with Two Stoppers

Frequency Band Broadening and Charge Density Enhancement of a Vibrational Triboelectric Nanogenerator with Two Stoppers

Flexible Layered-Graphene Charge Modulation for Highly Stable Triboelectric Nanogenerator.

The continuous quest to enhance the output performance of triboelectric nanogenerators (TENGs) based on the surface charge density of the tribolayer has motivated researchers to harvest mechanical energy efficiently. Most of the previous work focused on the enhancement of negative triboelectric charges. The enhancement of charge density over positive tribolayer has been less investigated. In this work, we developed a layer-by-layer assembled multilayer graphene-based TENG to enhance the charge density by creatively introducing a charge trapping layer (CTL) Al2O3 in between the positive triboelectric layer and conducting electrode to construct an attractive flexible TENG. Based on the experimental results, the optimized three layers of graphene TENG (3L-Gr-TENG) with CTL showed a 30-fold enhancement in output power compared to its counterpart, 3L-Gr-TENG without CTL. This remarkably enhanced performance can be ascribed to the synergistic effect between the optimized graphene layers with high dielectric CTL. Moreover, the device exhibited outstanding stability after continuous operation of >2000 cycles. Additionally, the device was capable of powering 20 green LEDs and sufficient to power an electronic timer with rectifying circuits. This research provides a new insight to improve the charge density of Gr-TENGs as energy harvesters for next-generation flexible electronics.

Growth of ZnO Nanorods on ITO Film for Piezoelectric Nanogenerators.

Piezoelectric nanogenerators (NGs) consist of zinc oxide nanorods (ZNRs), and polydimethylsiloxane (PDMS) layers were fabricated on indium tin oxide (ITO)-coated substrate for the energy harvesting system. The formation of seed layers by an optimized aqueous solution method greatly helped the growth of well-aligned ZNRs for NGs. Polyethylenimine (PEI) was added to increase the aspect ratio of ZNRs, which reached up to 24:1, showing the best energy harvesting performance of NGs. The formation of PDMS layers on the ZNRs increased the work function difference for the top Ag electrode. The thickness of PDMS layers was optimized as 80 μm, which showed the maximum work function difference, resulting in the enhancement of charge density. Piezoelectric NGs made of ZNRs of the highest aspect ratio of 24:1 with an 80-μm-thick PDMS layer achieved the highest current density of 2270.1 nA/cm2, which could be sufficient to drive low-power electronics.

Understanding charge transfer on the clinically used conical Utah electrode array: charge storage capacity, electrochemical impedance spectroscopy and effective electrode area

Objective. The Utah electrode is used for pre/clinical studies on neural recording and stimulation. Anecdotal and empirical reports on their performance have been made, resulting in variable testing methods. An in depth investigation was performed to understand the electrochemical behaviour and charge transfer mechanisms occurring on these clinically important electrodes. The impact of electrode geometry and material on performance was determined. Approach. Platinum and iridium electrodes were assessed by cyclic voltammetry and electrochemical impedance spectroscopy. The effective electrode area was measured by reduction of Ru(NH3)6 3+. Main results. Pristine Utah electrodes have little to no oxide present and the surface roughness is less than the diffusion length of Ru(NH3)6 3+ during voltammetry, which was ∼30 µm. Pristine iridium electrodes pass charge through capacitance and oxide formation. Hydride and anion adsorption occurs on the platinum electrode. Anodic current oxidises both metal surfaces, altering the charge transfer mechanisms at the electrode-solution interface. Charge storage capacity depends on measurement technique and electrode structure, this simplified number ignores more detailed information on charge transfer mechanisms that can be obtained from cyclic voltammetry. Electrode oxidation increases pseudocapacitance, reducing impedance. Charge transfer was non-homogeneous, most likely due to the electrode geometry enhancing charge density at the electrode tip and base. Oxidation of the electrode surface enhanced charge transfer inhomogeneity. The effective electrode area could be measured by reduction of Ru(NH3)6 3+ and calculated with a finite cone geometry. Significance. Increasing electrode pseudocapacitance, demonstrated by metal oxidation, reduces impedance. Increasing electrode capacitance offers a potential route to reducing thermal noise and increasing signal-to-noise ratio of neural recording. The effective electrode area of conical electrodes can be measured. The charge density of the conical electrode was greater than expected compared to a planar disc electrode, indicating modification of electrode geometry can increase an electrodes safe charge injection capacity. in vivo electrochemical measurements often do not include sufficient details to understand the electrode behaviour. Electrode oxidation most likely accounts for a significant amount of variation in previously published Utah electrode impedance data.

Cooperativity effects between regium-bonding and pnicogen-bonding interactions in ternary MF···PH3O···MF (M = Cu, Ag, Au): an ab initio study

Cooperativity effects between a regium-bonding and a pnicogen-bonding interactions in a series of MF···PH3O···MF (M = Cu, Ag, Au) ternary complexes are investigated using theoretical calculations at the MP2/aug-cc-pVTZ(-PP) level. Except for the AuF···PH3O···AuF complex, a pnicogen bond and a regium bond can coexist in each ternary complex. The calculated cooperativity energies are all negative, which demonstrates a positive cooperativity between the pnicogen- and regium-bonding interaction. For each series of ternary complexes, the effect of a regium-bonding interaction on a pnicogen bond is more pronounced than that of a pnicogen bond on a regium bond. Quantum theory of atoms in molecules (QTAIM), electron density difference (EDD) and natural bond orbital (NBO) analyses are extremely useful to understand the mechanism of the cooperativity effects of pnicogen- and regium-bonding interactions. These calculations indicate enhanced charge density values, charge transfer values and second-order perturbation energies for both pnicogen- and regium-bonding interactions in the ternary complex as compared to the isolated binary systems. The cooperative mechanism of both interactions is mainly electrostatic.

Interfacial electric field enhanced charge density for robust triboelectric nanogenerators by tailoring metal/perovskite Schottky junction

Regulating the dynamic behavior of triboelectric charges between dielectric layer and metallic electrode is a promising solution to suppress charge screen effect and to improve the output performances of triboelectric nanogenerators (TENGs). Herein, the cutting-edge inorganic CsPbBr 3 perovskite is used as a dielectric material to tailor metal/perovskite Schottky junction for robust TENG applications. Arising from the induced electric field, the electron transfer from perovskite to metallic nanoparticle significantly promotes the charge accumulation at the bottom electrode, which in turn increases the overall power output of TENGs. After precisely regulating the barrier height of Schottky junction by means of optimizing noble metals (Ag, Au, and Pt) and fabricating the bulk Schottky junction, the electron drift-diffusion processes and the triboelectric charge storage behavior have been carefully optimized, achieving an enhanced power density of 3.31 W m −2 with an open-circuit voltage up to 240 V and a short-circuit current density of 4.13 μA cm −2 . This work may give new insights into the dynamic behavior of triboelectric charges for advanced TENG platforms. A metal/perovskite Schottky junction is fabricated to increase the charge density for triboelectric nanogenerators (TENGs), significantly promoting the output performance to 3.31 W m −2 with voltage up to 240 V. • All-inorganic CsPbBr 3 perovskite film is employed as a triboelectric layer in TENG. • A metal/perovskite Schottky junction is fabricated at the FTO/CsPbBr 3 interface. • The charge drift and diffusion processes have been significantly suppressed. • A nearly 61% improvement in current density has been obtained. • The optimized TENG achieves an enhanced power density of 3.31 W m −2 with a V oc of 240 V.

Relative Efficacy of Co−X4 Embedded Graphene (X=N, S, B, and P) Electrocatalysts towards Hydrogen Evolution Reaction: Is Nitrogen Really the Best Choice?

AbstractWe perform first‐principles calculations to investigate whether or not nitrogen is the best dopant in system of Co−X4 embedded graphene (X=N, S, B, and P) electrocatalysts towards hydrogen evolution reaction(HER). Our theoretical results reveal that N, S, B, and P‐doped graphene can enhance the catalytic activity toward HER compared with the pristine graphene, and S doped graphene exhibits more favorable performance than N doped graphene, consistent with the experimental results. For the Co−X4 embedded graphene (X=N, S, B, and P), we predict that S may be a promising dopant in graphene supported single atom Co. The rather low hydrogen adsorption free energy (−0.07 eV) and activation energy barrier (0.78 eV) for the rate‐determining step, the downshift of the d band center, the enhanced charge density of dz2 orbital as well as the reduced work function are responsible for the unexpected activity of Co‐S4 embedded graphene for HER. Overall, Co‐S4 embedded graphene catalyst could be a good candidate for hydrogen evolution reaction.

Adsorption and Thermal Decomposition of Electrolytes on Nanometer Magnesium Oxide: An in Situ 13C MAS NMR Study

Mg batteries have been proposed as potential alternatives to lithium-ion batteries because of their lower cost, higher safety, and enhanced charge density. However, the Mg metal readily oxidizes when exposed to an oxidizer to form a thin MgO passivation surface layer that blocks the transport of Mg2+ across the solid electrode-electrolyte interface (SEI). In this work, the adsorption and thermal decomposition of diglyme (G2) and electrolytes containing Mg(TFSI)2 in G2 on 10 nm-sized MgO particles are evaluated by a combination of in situ 13C single-pulse, surface-sensitive 1H-13C cross-polarization (CP) magic-angle spinning (MAS) nuclear magnetic resonance, and quantum chemistry calculations. At 180 °C, neat G2 decomposes on MgO to form surface-adsorbed -OCH3 groups that are captured as a distinctive peak located at about 50 ppm in the CP/MAS spectrum. At low Mg(TFSI)2 salt concentration, the main solvation structure in this electrolyte is solvent-separated ion pairs without extensive Mg-TFSI contact ion pairs. G2, likely including a small amount of G2-solvated Mg2+, adsorbs onto the MgO surface. At high Mg(TFSI)2 salt concentrations, contact ion pairs between Mg and TFSI are formed extensively in the solution with the first solvation shell containing one pair of Mg-TFSI and two G2 molecules and the second solvation shell containing up to six G2 molecules, namely, MgTFSI(G2)2(G2)6+. In the presence of MgO, MgTFSI(G2)2(G2)6+ adsorbs onto the MgO surface. At 180 °C, the MgO surface stimulates a desolvation process converting MgTFSI(G2)2(G2)6+ to MgTFSI(G2)2+ and releasing G2 molecules from the second solvation shell of the MgTFSI(G2)2(G2)6+ cluster into the solution. MgTFSI(G2)2+ and MgTFSI(G2)2(G2)6+ tightly adsorb onto the MgO surface and are observed by 1H-13C CP/MAS experiments. The results contained herein show that electrolyte composition has a directing role in the species present on the electrode surface, which has implications on the structures and constituents of the solid-electrolyte interface on working electrodes and can be used to better understand its formation and the failure modes of batteries.

Coexistence of Superconductivity with Enhanced Charge Density Wave Order in the Two-Dimensional Limit of TaSe2.

Bulk 2H-TaSe2 is a model charge density wave (CDW) metal with superconductivity emerging at extremely low temperature (Tc = 0.1 K). Here, by first-principles calculations including the explicit calculation of the screened Coulomb interaction, we demonstrate enhanced superconductivity in the CDW state of monolayer 1H-TaSe2 observed in recent experiments. Its ground-state 3 × 3 CDW phase features triangular clustering of Ta atoms and possesses a large electron-phonon coupling of λ = 0.74, yielding an order of magnitude higher superconducting Tc compared to the bulk. Upon lowering the thickness from bulk to monolayer TaSe2, the CDW intensifies with slightly decreased Fermi-level density of states, while superconductivity gets boosted via a largely increased intrinsic electron-phonon coupling strength, which overcomes both the CDW effect and naturally reinforced Coulomb repulsion. These results uncover the simultaneously enhanced CDW and superconducting orders in the two-dimensional limit for the first time and have key implications for other CDW metals like 2H-TaS2.

Polysaccharide Hydrogel Incorporated Carbon Nanofiber Microelectrode for Designing Neural Interfaces

Bionic devices are an integral part of human life, and continuous innovations in their design and functions with the help of nanotechnology has revolutionized the area of neuroscience and technology. Bio-interfaces play a key role in bionic devices such as neural implants for efficient transfer of the signal to smart prosthetics. We report here on the design of a new microelectrode, comprising Carbon Nanofiber (CNF) and a biopolymer, namely carboxymethyl xyloglucan (CMX) hydrogel inside the CNF, which enhances the current density across the interface. Microelectrode was prepared by in-situ cross-linking of CMX inside CNF, with optimized CMX: CNF ratio, resulting in continuous ionic channels confined within the hollow core of CNF. Electron microscopy images of microelectrodes illustrate the formation of CMX hydrogel network inside the CNF hollow core without wrapping its surface. The presence of hydrogel in the CNF was confirmed by Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). The electrochemical studies indicate the enhancement in charge density as well as the active surface area of the microelectrodes due to the presence of CMX hydrogel network. These microelectrodes have great potential as neural interfaces for designing smart prosthetics with voluntary control.