Volumetric Charge Density Research Articles

A high-output performance disc-shaped liquid-solid triboelectric nanogenerator for harvesting omnidirectional ultra-low-frequency natural vibration energy

Low-frequency vibrations, such as ocean waves, are widely distributed in nature and serve as a promising renewable energy source. Triboelectric nanogenerators (TENGs) have been shown to be an effective method for harvesting low-frequency vibration energy. However, most TENGs can only effectively harvest vibration energy in a single direction and a specific vibration mode. To solve the problem, we developed a disc-shaped liquid-solid triboelectric nano-generator (DLS-TENG) that can harvest vibration energy omnidirectionally. Benefiting from the high flexibility of the fluid and the ultra-high surface utilization of the disc structure, the DLS-TENG has the highest volumetric charge density and load driving capability in harvesting omnidirectional vibrational energy. Driven by seesaw vibrations with a frequency of 0.5 Hz and an amplitude of 30°, one DLS-TENG successfully lit up 544 LEDs simultaneously, with a transferred charge of 1263 nC. Considering the random, irregular, and variable characteristics of most ambient vibrations, our omnidirectional TENG is more practical. The proposed DLS-TENG can achieve long-term and efficient natural vibration energy harvesting to power an increasing number of microsensors widely distributed in the field.

Theoretical investigation of the growth of GaAs on Si(001), Si(110), Si(111), Si(113) and Si(331)

The atomic structure of the first atomic layers of GaAs over Si(hhl) substrates were studied by ab initio calculations employing the density functional theory (DFT). Layered converged Si(hhl) supercells were used to investigate the interfacial interaction with the first Ga/GaAs and As/GaAs layers. Formation energies and volumetric charge densities differences confirms the stronger tendency of the As atoms, compared to Ga atoms, to form bonds with the different Si(hhl) surfaces. We confirm the reported experimental order sequence Si(111) > Si(001) > Si(110) in internal crystal structure quality of GaAs growth via the calculation of the interfacial energy, work of adhesion and total charge transfer. From this work, we expand the sequence in internal crystal structure quality as Si(111) > Si(331) ≥ Si(001) > Si(113) ≥ Si(110).

A numerical study supplemented with theoretical analysis on streaming potential in a soft nanochannel influenced by ion partitioning and mobile surface charge-dependent wall slip

We consider the pressure-driven flow of an electrolyte in a soft channel with a hydrophobic charged surface coated with a diffuse polyelectrolyte layer (PEL) with constant volumetric charge density. The objectives are to enhance the streaming potential and electrochemical energy conversion efficiency in the modulated soft channel as well as to examine the influence of surface charge mobility-dependent slip velocity on the electrokinetics. The laterally mobile adsorbed surface charge modifies the slip velocity condition, which is coupled with the induced streaming potential. The ion partitioning effect arises due to the step change in dielectric constant between the PEL and the electrolyte that modifies the distribution of ions, which is incorporated through the Born energy difference of ions. The nonlinear coupled set of equations governing the electrokinetics in a soft channel is solved numerically through a control volume approach. A simplified model based on the Debye–Hückel approximation under certain limiting conditions is also derived, which compares well with the present numerical model for a lower range of charge density and non-overlapping Debye layers. We find that a modulation of a nanochannel by coating a PEL of lower dielectric constant on hydrophobic charged walls can significantly enhance the streaming current and energy conversion efficiency. In contrast with existing studies, we find that the mobile surface charge can have a positive impact on the electrochemical energy conversion efficiency in a soft nanochannel. The mobility of the surface charge attenuates the streaming current in a PEL-free channel and can enhance the streaming current for a suitable choice of PEL volumetric charge density.

Gas-liquid two-phase flow-based triboelectric nanogenerator with ultrahigh output power.

Solid-liquid triboelectric nanogenerators (SL-TENGs) have shown promising prospects in energy harvesting and application from water resources. However, the low contact separation speed, small contact area, and long contacting time during solid-liquid electrification severely limit their output properties and further applications. Here, by leveraging the rheological properties of gas-liquid two-phase flow and the Venturi-like design, we circumvent these limitations and develop a previously unknown gas-liquid two-phase flow-based TENG (GL-TENG) that can achieve ultrahigh voltage and volumetric charge density of 3789 volts and 859 millicoulombs per cubic meter, respectively. With a high-power output of 143.6 kilowatts per cubic meter, a 24-watt commercial lamp can be directly lighted by a continuous-flow GL-TENG device. The high performance displayed SL-TENGs in this work provides a promising strategy for the practical application of solid-liquid TENGs in energy harvesting and sensing applications.

All‐Printed Wearable Triboelectric Nanogenerator with Ultra‐Charged Electron Accumulation Polymers Based on MXene Nanoflakes

AbstractThe multilayer triboelectric nanogenerators (TENGs) are widely developed to enhance the output performance of device. However, these TENGs consisting of electron transfer, transport, trap layers toward a large volumetric charge density should be wearable and mass‐produced for commercialization. Thus, appropriate material selection in respective layers and fabrication method are crucial for the commercialization of multilayer TENG. This study presents all‐printed, sustainable wearable TENGs based on electron accumulation polymers (EAPs) with superior charge retention capability. The EAPs consisting of polytetrafluoroethylene (PTFE), carboxyl functionalized single‐walled carbon nanotubes (SWCNTs:COOH), and Ti3C2Tx (MXene) in a fluorinated polymer matrix, are used. Compared to the reference, the EAPs not only lead to approximately six times higher output performance (300 V and 40 µA) but also four times more sustainable charge retention capability (92%) for an hour. These are attributed to the three‐step electron‐trapping mechanism with electron transfer/transport from PTFE/SWCNT and electron trapping in MXene. In addition, TENGs with EAPs exhibit excellent mechanical stability and reliability with fascinating single‐electrode demonstrations. Finally, the TENG with EAPs can efficiently operate various portable electronics and pH monitoring systems with a pH sensor and a seven‐segment display in realistic scenarios.

Integrating exceptional visible modulation, near-infrared shielding and energy storage in an all-solid-electrochromic bilayer device

A generic strategy of incorporating diverse functions in electrochromic dynamic windows is presented by sensibly choosing the individual layers of a bilayered active electrode. Here, all-solid electrochromic devices (ECD) with a remarkably high visible modulation (60–80%) and superior near-infrared (NIR) shielding performance (>90% full scale) were fabricated by simple solution-processing. The concept is demonstrated by selecting materials with identical chemical composition, i.e., porous amorphous-WO3 (a-WO3) coated on top of polycrystalline WO3·H2O nanosheets. These ECDs show four distinct voltage-selective modes in the ± 2.8 V range for enhanced privacy and energy saving. The IR modulation efficiency (IRME) of the devices stands at a record ~85%, with an outstanding solar modulation efficiency (SME) of ~63%. The initial energy storage estimations for the ECDs revealed superior volumetric stored charge density of ~400 Ccm−3@ 10 mVs−1, which is excellent for secondary energy sourcing. The fabricated EC glasses (with 50% usage) could directly save ~165 kWhm-2 yr-1 worth of energy by equating the energy-saving and generation. With reflected radiation reduction, the total saving may surpass the total energy generation from standard Si-Solar cells (~18% efficiency) of equal areal coverage.

Multi‐Mode Water‐Tube‐Based Triboelectric Nanogenerator Designed for Low‐Frequency Energy Harvesting with Ultrahigh Volumetric Charge Density

AbstractVast renewable energies are contained in mechanical motions in nature such as ocean waves. However, it is challenging to effectively harness these energy sources due to their low frequency and irregularity. Triboelectric nanogenerators (TENGs) are a promising technology for renewable energy conversion, but conventional TENGs suffer from challenges including single‐mode operation, low contact intimacy, and material abrasion. Here, by encapsulating deionized DI water into a fluorinated ethylene‐propylene tube, a versatile and high‐performance water‐tube‐based TENG (WT‐TENG) is developed. Benefiting from the high flexibility of the water, the WT‐TENG can work at various operation modes and generate power from multiple mechanical energy sources. With the intimate water/solid contact, the WT‐TENG achieves an ultrahigh volumetric output charge density of 9 mC m−3 at a frequency of 0.25 Hz, beyond all previous reports. Moreover, multiple finger‐sized WT‐TENG units can be easily integrated as one device and realize multiplied outputs. A wearable body motion energy harvester and a water wave energy harvester are demonstrated as examples of the WT‐TENG applications. The proposed WT‐TENG can be regarded as a new brick for the TENG mansion, and numerous applications could be built up based on the WT‐TENG units.

Asymmetric PEDOT:PSS Trilayers as Actuating and Sensing Linear Artificial Muscles

AbstractSoft ionic actuators and sensors have been intensively studied over the last 20 years. The bending trilayer configuration has been considered a standard architecture, allowing the development of new materials and their optimization. However, bending deformation remains low in force output and presents limited integration capabilities in fast emerging fields like humanoid robotics and actuating textiles. A generalizable architecture of asymmetric supercapacitor‐like trilayers is presented to develop open‐air linear artificial muscles that actuate and sense. First, tuning of electromechanical properties of asymmetric electrodes is performed separately by combining poly(3,4‐ethyl‐enedioxythiophene):poly(styrene sulfonate) with a polyethylene oxide network and 1‐ethyl‐3methylimidazolium bis(trifluoromethanesulfonyl)imide as additives. By varying their content, electronic conductivity can be tuned between 20 and 457 S cm−1, Young's modulus from 1.5 to 0.27 GPa, and volumetric charge density increased by 36%. Asymmetric trilayers are then fabricated using a simple layer stacking process by selecting the optimal combination of materials according to an electromechanical model. Linear strain of 0.5% is obtained in 30 s under ±2 V with 70% of the deformation within 5 s and blocking stress as high as 0.3 MPa. When mechanically stimulated, these asymmetric trilayers demonstrate linear sensing as well, with a sensitivity of 0.38 mV %−1.

Electro-interpenetration as tool for high strain trilayer conducting polymer actuator

Electrochemical actuators based on electronic conducting polymers can convert electrical energy into mechanical work. The amplitude of the electromechanical response is related on volumetric charge density of conducting polymer electrodes and strain-to-charge ratio, an empiric electromechanical coupling parameter. In this work we describe the elaboration of high performance trilayer bending actuators by the electro-interpenetration of a conducting polymer, i.e. poly(3,4-ethylenedioxythiophene) (PEDOT), within a host membrane. The host membrane is first elaborated as an interpenetrating polymer networks combining nitrile butadiene rubber network and poly(ethylene oxide) network. An oxidative chemical prepolymerization of EDOT allows turning the host membrane into conductive substrate suitable for subsequent electropolymerization. The electropolymerization of EDOT from the chemically polymerized layer allows controlled interpenetration of PEDOT underneath the surface. A significant increase of local concentration of PEDOT in the electrodes, compared to those obtained from oxidative polymerization lead to a significant increase of the charge density. The polymerization conditions do not have significant impact on sign and absolute value of strain-to-charge ratio, but it can be improved by the nature of the electrolyte. The combination of these two effects leads to an actuator with up to 15% of strain difference.

A physico-chemical study of the interaction of ethanolic extracts of propolis with bacterial cells

In the present study, an effort has been made to understand the interaction mode of propolis, a natural substance produced by honey bees, with gram-positive and gram-negative bacterial cells by measuring alterations in cell surface physico-chemical properties following the incubation of the cells with different sub-inhibitory concentrations of this antimicrobial agent. Electrophoretic mobility and surface hydrophobicity measurements revealed for the first time that propolis induced substantial changes in the volumetric charge density, electrophoretic softness and degree of hydrophobicity characterizing the outermost surface layer of cells. These changes, which appear to be dose-dependent, seem to be consistent with the increasing accumulation and penetration of the propolis antimicrobial components through the cells extracellular layer. Moreover, electron microscopy observation and the determination of the cell constituents’ release demonstrated that propolis at sub-bactericidal concentrations already provoked (at least localized) cell wall damage and/or perturbations. These findings thus suggest that the initial mechanism of action of propolis is most likely structural, resulting from sufficient interaction between the different propolis components and bacterial cell wall structures.

Analysis of Mg2+/Li+ separation mechanism by charged nanofiltration membranes: visual simulation

The mechanism of the nanofiltration (NF) membrane separation of Mg2+ and Li+ needs to be further investigated, but some commonly used model theories are abstract, which makes them difficult to understand. More importantly, the relationship between the membrane charge and separation performance of Mg2+ and Li+ cannot be quantitatively analyzed. It is worth studying these challenges and providing a performance boost for Mg2+/Li+ filtration applications of NF membranes. Here, various NF membranes, with the membrane volumetric charge density increasing from −4.69 to 7.02 mol · m−3, were fabricated via interfacial polymerization. For these membranes, the separation factor S Mg,Li was decreased from 0.41 to 0.20. Importantly, the visual simulation results were consistent with the experimental results as a whole. The separation factor S Mg,Li decreased with the increase of volumetric charge density, and the minimum separation factor S Mg,Li of the NF membranes was 0.20 (experiment) and 0.17 (simulation), respectively. This meant that the performance of the positively charged NF membrane was not fully developed. Furthermore, we analyzed the relationship between the membrane charge and separation performance, and visualized the simulation of the NF membrane filtration and separation.

On the permselectivity of cation-exchange membranes bearing an ion selective coating

Monovalent ion selective membranes are permeable for monovalent ions while rejecting divalent ions to some extent. Different processes and applications like electrodialysis, microbial fuel cells, and flow batteries utilize such selective properties. Industrial membranes have a specific coating of equal charge to reject the bivalent counter ions. It has been suggested in the past that the current density regime at which such composite ion exchange membranes are operated can strongly influence their ion selectivity towards monovalent ions. Here, we now confirm this observation for a commercial CMS membrane as well as for a novel microgel modified membrane. The higher the applied current density is, the more acute the drop in selectivity becomes as opposed to the unmodified reference membrane where bivalent ions are transported preferentially. This work focuses on the relationship between selectivity and current density regime using (1) a conventional commercial membrane, (2) a commercial monovalent ion selective membranes as well as (3) a tailor-made selective membrane, the latter being surface-modified with quaternized Poly (2-vinylpyridine) (qP2VP) microgels. Experimental electrodialysis results in combination with (a) direct numerical simulations of mixed ion transport through the composite architecture and (b) a swelling analysis of the microgels by ellipsometry reveal that layer responsiveness and structural change of the modification layer is responsible for the decrease in permselectictivity upon an increased current density. The swelling reduces the charge density of the modification and therewith the rejection of divalent ions. It would be highly desirable to synthesize modification layers that have a low ion transport resistance while maintaining its volumetric charge density independent of the current density applied.

Standardizing the Scattering Process in Experimental Gas Electron Diffractometry

A solution is sought for problems in experimental gas electron diffractometry. An experiment is performed that meets the requirements of the International Organization for Standardization for measuring processes and equipment. The scattering process is expressed through the densities of volumetric charge density fluxes transferred through the irradiated volume. The advantages of a molecular beam as a target for fast electrons of the probe are demonstrated. It is proposed that the ratio of attained results to used resources be used for quantitative estimates of the efficiency of a measuring system. The efficiencies of an electron source of an electron diffractometer, a target, and an instrument background manufactured at the laboratory of Moscow State University are estimated as $${{\sigma }_{{1(S = 28{{{\AA}}^{{ - 1}}})}}}$$ = 6.36 × 10−18, $${{\sigma }_{{2(S = 28{{{\AA}}^{{ - 1}}})}}}$$ = 2.24 × 10−11, and $${{\sigma }_{{0(S = 28{{{\AA}}^{{ - 1}}}){\text{back}}}}}$$ = 1.06 × 10−20, respectively. It is established that the detection of a useful signal at S = 28 A−1 requires the transfer of a probe charge of 2.2 × 105 C through the irradiated volume at a target charge of 6.25 × 10−2 C and a signal/noise ratio of 870 at S = 28 A−1.

Stress-charge coupling coefficient for thin-film polypyrrole actuators – Investigation of capacitive ion exchange in the oxidized state

This work quantifies the actuation behavior of thin electrodeposited polypyrrole films on rigid substrates. During in situ cantilever bending experiments in aqueous perchloric acid, the films remain clamped to their substrate and the film stress is inferred from a small bending of the cantilever. The potential range under study is 0.4–0.8 V versus the standard hydrogen electrode. Within this potential region, the film is in the oxidized state and the actuation arises from capacitive electrode processes. For the volumetric capacitance, c*, we find 0.24±0.01F/mm3. The stress-charge coupling coefficient, ξ, which is defined as the stress variation per volumetric charge density, emerges as −153±11mV. The results are robust, reproducible and independent of the film thickness or the potential scan rate. The experimental value of ξ is supported by an independent estimate, based on a micromechanical model in combination with literature data for the partial molar volume of solvated perchlorate anions and the elastic constants of polypyrrole.

Electrohydrodynamic formation of single and double emulsions for low interfacial tension multiphase systems within microfluidics

The feasibility of droplet formation from the dispersion of one viscous fluid within another immiscible viscous fluid with low interfacial tension is shown to be very limited. In this work, the process of emulsion formation for low interfacial tension multiphase systems (e.g. aqueous two-phase systems (ATPSs)) was simulated, where the liquids were exposed to an electric field within a microfluidic device. For the first time, the formation of double emulsion via electrohydrodynamic (EHD) force within microfluidics was investigated. A three dimensional (3D) numerical model was developed based on finite-volume discretization of the governing equations to simulate the EHD-based single and double emulsion formation for ATPSs within microfluidics. The dispersed viscous phase moving toward the active electrode is subjected to shear stress, producing instability on the two-phase interface and causing the formation of a necking area. Upon removal of the electric pulse, the dispersed phase moves in the opposite direction resulting in the formation of the droplet. The volume-of-fluid numerical method was applied to trace the two-phase interface, and a height function was imposed to deal with the 3D contact angles. The effect of capillary number and permittivity ratio of the phases on the size and shape of the droplets was assessed and compared with experimental data. Through controlling the interface between the phases, pressure contours, and volumetric charge density contours, it is possible to generate EHD-based single and double emulsions from viscous fluids within microfluidics with applications in drug delivery, tissue engineering and chemical and biological processes.

Perfect relativistic magnetohydrodynamics around black holes in horizon penetrating coordinates

Plasma accreting processes on black holes represent a central problem for relativistic astrophysics. In this context, here we specifically revisit the classical Ruffini-Wilson work developed for analytically modeling via geodesic equations the accretion of perfect magnetized plasma on a rotating Kerr black hole. Introducing the horizon penetrating coordinates found by Doran 25 years later, we revisit the entire approach studying Maxwell invariants, electric and magnetic fields, volumetric charge density and electromagnetic total energy. We finally discuss the physical implications of this analysis.

Ultrathin electrochemically driven conducting polymer actuators: fabrication and electrochemomechanical characterization

Electronic conducting polymer based-actuators have attracted lots of interest as alternative materials to traditional piezoelectric and electrostatic actuators. Their specific characteristics such as their low operating voltages and large strains should allow them to adapt better to soft microstructures. Recently, poly (3,4-ethylenedioxythiophene) (PEDOT) – based ionic actuators have overcome some initial stumbling blocks to widespread applications in the microfabricated devices field. These trilayer bending microactuators were fabricated (i) by sequential stacking, using a layer by layer polymerization (LbL) of conducting polymer electrodes and a solid polymer electrolyte and (ii) by micro-patterning, using standard microsystems processes. While microfabrication processing of a trilayer actuator, involving no manual handling has been demonstrated, their bending performances remain limited for practical applications. Moreover, the complete characterization of their electrical, electrochemical, and mechanical properties has never been investigated. This paper describes the optimization of PEDOT electroactive electrodes synthesized with a vapor phase polymerization process. Influence of synthesis parameters on thickness, electronic conductivity and volumetric charge density were studied to determine the guidelines for synthesizing highly efficient electrodes. Afterwards, these parameters are used to guide the LbL synthesis process of ultrathin trilayer actuators. Electrochemical and mechanical properties of the resulting microactuators have been thoroughly characterized. Bending deformation and output force generation have been measured and reached 0.5% and 11 μN respectively. This constitutes the first characterization of ionic PEDOT-based microactuators operating in air of such a thin thickness (11 μm dry and 18.3 μm swelled in 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImTFSI)). These actuators and their actuation properties are promising for future soft microsystem devices where the use of polymer actuators should be essential.

Electrochemical Formation and Characterization of Surface Blocking Layers on Gold and Platinum by Oxygen Reduction in Mg(ClO4)2 in DMSO

Metal-oxygen batteries employing non-aqueous electrolytes are a promising alternative to conventional lithium-ion batteries due to their high specific energies. One of the most appealing metals in such an application is magnesium, considering its price and its volumetric charge density. While previous reports already indicated the formation of a blocking layer on the oxygen-electrode surface during oxygen reduction, associated with a low reversibility, the reasons for this behavior are not yet understood. This work focuses on elucidating the composition as well as the electrochemical behavior of this blocking layer employing X-ray photoelectron spectroscopy, infrared spectroscopy and measurements with a rotating ring-disc electrode setup. The electrochemical measurements indicate that the blocking layer exhibits an effect similar to the valve effect, which is known from the oxidation of aluminum for example. Combining potentiodynamic and –static measurements, it could be shown that there is a current flow at cathodic potentials due to migration of ions within the layer. A further outcome of the electrochemical measurements is that the anodization of this surface layer proceeds in a self-accelerating manner. The spectroscopic analysis of the surface layer suggests the formation of magnesium peroxide on the surface as well as the presence of some sulfur and chloride containing compounds which must arise from the decomposition of the electrolyte.

Counter-ion transport number and membrane potential in working membrane systems

In this work we use the general space-charge (SC) theory for a combined transport model of fluid and ion through cylindrical nanopores to derive equations for the membrane potential and counter-ion transport numbers. We discuss this approach for ion exchange membranes assuming aqueous domains as interconnected network of cylindrical pores. The transport number calculations from the SC theory are compared with the corresponding ones from the uniform potential (UP) and Teorell-Meyer-Sievers (TMS) models in the case of both zero and non-zero concentration gradient across the membrane and with an applied current density. By using this approach we suggest the optimal conditions for performing membrane potential experiments (i.e. choice of electrolyte and concentration difference) depending on an easily accessible membrane property, namely the volumetric charge density. We also theoretically describe a novel dynamic method to determine in a single experiment the membrane potential and membrane conductivity. To exemplify the use of the dynamic method we report the calculations based on typical operating conditions of the reverse electrodialysis process. The numerical results are presented in terms of the electrical potential difference versus the average pore radius and charge density. The resulting map is a useful tool for a rational design of an effective membrane morphology for a specific electrochemical application.

Electrophoresis of soft particles with charged rigid core coated with pH-regulated polyelectrolyte layer

We present a theoretical study on the electrophoresis of a soft particle with a dielectric charged rigid core grafted with a charge-regulated polyelectrolyte layer. The polyelectrolyte layer possesses either an acidic or a basic functional group and the charge dissociation depends on the local pH and ionic concentration of the electrolyte. The dielectric rigid core is considered to possess a uniform volumetric charge density. The electric potential distribution is determined by computing the Poisson-Boltzmann equation outside the core coupled with a Poisson equation inside the impermeable core along with suitable matching conditions at the core-shell interface. The computed electric field is used to determine the mobility of the particle through an existing analytic expression based on the Debye-Huckel approximation. Our results are found to be in good agreement with the existing solutions for the limiting cases. The influence of the core charge density, ionic concentration, and pH of the electrolyte on the particle mobility is studied for different choice of hydrodynamic penetration length of the polyelectrolyte and dissociation constant of the functional group. The critical value of the pH required to achieve zero mobility is estimated. We find that in a monovalent electrolyte solution, the soft particle with a net negative (positive) charge can have positive (negative) mobility.