Positive Charge Density Research Articles

Hyperbranched Polymer Network Based on Electrostatic Interaction for Anodes in Lithium-Ion Batteries.

Silicon is considered as one of the ideal anode materials for the new generation of lithium-ion batteries due to its extremely high theoretical specific capacity. Nevertheless, in the actual charging and discharging process, the Si electrode will lose its electrochemical performance due to the huge volume change of Si nanoparticles resulting in detachment from the surface of the fluid collector. The polymer binder can bond the Si nanoparticles together in a three-dimensional cross-linking network, which can thus effectively prevent the Si nanoparticles from falling off the surface of the fluid collector due to the drastic change of volume during the charging and discharging process. Therefore, this study developed a new polymer binder based on electrostatic interaction with hyperbranched polyethylenimine (HPEI) as the main body and water-soluble carboxylated polyethylene glycol (CPEG) as the cross-linker, where the degree of cross-linking can be easily optimized by adjusting the pH value. The results demonstrate that, when the density of positive and negative charges in the binder is relatively balanced at pH 7, the stability of the battery's charge-discharge cycle is significantly improved. After 200 cycles of constant current charge-discharge test, the specific capacity retention rate is 63.3%.

Polyamide nanofiltration membranes with rigid–flexible microstructures for high-efficiency Mg2+/Li+ separation

Lithium extraction from salt-lake brine with a high Mg2+/Li+ ratio is crucial for mitigating lithium supply shortage. Positively charged polyamide nanofiltration membranes, which are often prepared by performing interfacial polymerization (IP) using polyethyleneimine and trimesoyl chloride, are considered to be promising candidates for Mg2+/Li+ separation owing to their high energy efficiency and low environmental impact. However, the performance of these membranes is severely hindered by “useless pores” and “defects” present in the flexible polyamide layer. Herein, we provide a facile strategy for modifying flexible semi-aromatic polyamide chains by intercalating a rigid electropositive monomer, histamine, to remold the internal pores and positive charge density at a molecular level. Two routes, namely, “swelling-embedding-reacting-shrinking (SERS)” and “in-situ interposition (SIP)” were used to construct a new polyamide layer with rigid–flexible microstructures. The fabricated SERS-0.50 membrane showed a 5-fold higher water flux and 2-fold increase in the Mg2+/Li+ separation factor compared with the IP membrane. Moreover, the SIP-0.15 membrane with an enhanced positive charge density exhibited a considerably higher Mg2+/Li+ separation factor (15.38, 500 % increase compared with that of the IP membrane) for brine with a Mg2+/Li+ ratio of 20. This study provides a reference for developing nanofiltration membranes used for high-efficiency Mg2+/Li+ separation.

Effect of Cationic Modified Microcrystalline Cellulose on the Emulsifying Properties and Water/Oil Interface Behavior of Soybean Protein Isolate.

Stabilizing emulsion using complex biopolymers is a common strategy. It would be very interesting to characterize the impact of charge density on the emulsifying properties of complex polyelectrolytes carrying opposite charges. In this study, cationic modified microcrystalline celluloses (CMCC) of different charge densities were prepared and mixed with soy protein isolate (SPI) for emulsion applications. CMCC-1 to 3 with various cationic charge values were successfully prepared as characterized by zeta-potential and FTIR. The positive charge density’s effects on solubility, thermogravimetric properties, and rheological properties were studied. Complexes of SPI-CMCC with various zeta-potential values were then obtained and used to stabilize soybean oil emulsions. The results show that emulsions stabilized by complexes of SPI and CMCC-3 at a ratio of 1:3 had the best emulsification ability and stability. However, the interfacial tension-reducing ability of complexes decreased continuously with increasing cationic charge value, while the rheological results show that complexes of SPI-CMCC-3 at a ratio of 1:3 formed a stronger viscoelastic network than other complexes. Our results indicate that this SPI-CMCC complex formula showed excellent emulsification performance, which could be adjusted and promoted by changing the charge density. This complex formula is promising for fabrication of emulsion-based food and cosmetic products.

Understanding Effects of Deep Traps on DC Surface Flashover Characteristics of Epoxy/MWCNTs-TiO2 Nanocomposites in a Vacuum

Surface flashover is likely to be triggered when a high electric field is applied due to its voltage being much lower than the breakdown voltage of either gas or solid, which restricts the development of advanced power electrical and electronic devices. To improve dc surface flashover performances in a vacuum and further explore the effects of deep traps on surface flashover, conductive multiwall carbon nanotubes (MWCNTs) and nonconductive nano-titania (TiO2) particles were incorporated into the epoxy (EP) matrix to tailor the surface deep trap level. Surface trap parameters, surface conductivity, surface charge density, and surface flashover voltage were calculated and measured. It indicates that surface flashover voltage improves by 23.07% and 14.45% compared to pristine EP when solely introducing MWCNTs or nano-TiO2 particles into the EP matrix, while it increases by 36.04% for C0.1T2 as simultaneously introducing both particles. When adding small amounts of particles, the surface charge transport is suppressed due to the introduction of bonded layers in the interfacial region, and the surface deep trap level is improved. As the surface deep trap level increases, charge transport and electron emission processes in the solid surface layer are hindered, which reduces the surface positive charge density and the distortion of the electric field and further results in the reduction of surface conductivity and the improvement of dc surface flashover voltage in a vacuum. The explanation for the effects of surface deep traps on surface flashover is essential for further improvements of surface flashover.

Salt-modified MXene membrane for ultrafast and efficient cationic and anionic dyes removal

MXene, the two-dimensional (2D) transition metal carbides/nitrides, have gained much attention in the application as membranes since the stacking of MXene nanosheets could realize hydrophilic, nanoscale interlayer spacing with remarkable separation performance. Herein, we reported the simple modification of MXene membranes using chloride salts (NaCl, KCl, and MgCl2), which could substantially improve the performance in the separation of cationic (methylene blue, MB) and anionic (congo red, CR) dyes from aqueous solutions. The salts could reside in the membrane surface and penetrate the interlayer galleries as well as the space within the adjacent MXene nanosheets. As a result, the membrane could possess modified nanochannels and altered surface chemistry that improve water transport and dye molecules' retention. In the case of MB filtration, MXene membrane modified with KCl (MM-KCl) exhibits the highest flux (141 L m−2 h−1) and a complete rejection, attributed to the weaker interaction between the water molecules and potassium ion. On the other hand, MM-MgCl2 demonstrates the best performance (flux of 117 L m−2 h−1 and a ∼100 % rejection) in the CR filtration. This could be related to the stronger interaction of anionic dye molecules with the magnesium cation that has the highest positive charge density. All MXene membranes have high flux-recovery ratios and low reversible and irreversible fouling, showing desirable anti-fouling properties.

Influence of 1,8-naphthalimide derivatives as additives on the electrodeposition of tin from methanesulfonic acid system

A series of 1,8-naphthalimide derivatives containing different quaternary ammonium groups have been synthesized by a two-step method. Electrochemical tests and quantum chemical calculations demonstrated that 1,8-naphthalimide parent conjugate ring adsorbed to the tin surface and occupied active sites, and positive charges on aromatic ring quaternary ammonium group competed with Sn2+ for electrons. Moreover, higher positive charge density and larger conjugate area of the aromatic ring quaternary ammonium group were considered to increase cathodic polarization to inhibit the deposition rate of tin ions and hydrogen evolution. The substituted naphthalimide NI4 which had a current density suppression effect of 90% and negatively shifted tin deposition and hydrogen evolution potential by 20 mV and 0.45 V respectively was deemed to be the best performed one on this basis. In actual tin plating, compared with base electrolyte, the tin layer surface under NI4 electrolyte was smoother at any current density and had no leakage or agglomeration. SEM showed a higher nuclei density with smaller feature size, and XRD demonstrated a shift in the dominant crystalline plane from (420) to (200).

Enhanced adsorption of inorganic arsenic by Mg-calcite under circumneutral conditions

Calcite is an important reservoir for arsenic (As) and strongly affects its mobility in various geological environments. However, the method by which bulk As is taken up by calcite needs to be better understood. To broaden our understanding, Mg-containing calcite (Mg-calcite), which is a ubiquitous form of calcite in nature, was investigated to determine its As adsorption capacity. Laboratory experiments were conducted under aerobic and anaerobic conditions using synthetic pure calcite (Ca10Mg0) and Mg-calcite (Ca9Mg1, Ca8Mg2). As speciation (determined using chromatography techniques, such as ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS)) and microscopic characterization (field-emission scanning electron microscopy coupled with energy-dispersive spectroscopy (FE-SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS)) were coupled to investigate the adsorption capacity and potential mechanisms of As adsorption by Mg-calcite. The results showed that Mg-calcite exhibited an As adsorption capacity that was several times higher than pure calcite, especially for As(III). Based on microscopic characterizations, the substitution of CO3/OH groups with As-O groups and the formation of complexes on the Mg-calcite surface are the dominant mechanisms of arsenate (As(V)) adsorption. The doping of Mg into calcite results in a lattice contraction effect that provides additional space for the substitution of larger As oxyanions for carbonate ions. In parallel, as evidenced by the potentiometric automatic titration results, the presence of Mg in calcite led to an increased density of surface positive charges, which promotes greater adsorption of negatively charged As. In addition to the substitution of CO3 groups with As-O groups, the enhanced adsorption of As(III) by Mg-calcite was also attributed to the larger amount of H-bonding yielded by the addition of Mg. To the best of our knowledge, this is the first experimental investigation to quantify the adsorption of As by Mg-calcite, and it provides new insights into the fate and transport of inorganic As by carbonates in aqueous environments.

Enabling two-electron redox chemistry of P-type organic cathode for high-capacity aluminium-ion batteries

P-type organic cathodes (p-OCs) hold great promise in aluminium-ion batteries (AIBs), however current p-OCs exhibit apparent one or less than one electron redox processes and low capacities. Herein, we report a compromised electron-donating substitution strategy to excite 1-aminopyrene (ANP), a pyrene (Pyr) derivative, to undergo two-electron transfer, achieving a high specific capacity of 212 mA g−1 and excellent rate/long cycling performances (e.g., 106 mAh g−1 at 10 A g−1 for 12,000 cycles), superior over reported organic AIB cathodes. The electronic and steric effects of substitutes in a variety of Pyr derivatives on their functionality have been revealed. The electron-donating effect of the amino group plays two different roles, one in favoring the electron removal of neutral Pyr derivatives, another in reducing the positive charge density of oxidized radical cations. Collectively, ANP with the compromised electron-donating effect exhibits the highest binding energy with AlCl4- and reasonable voltage within the electrolyte working threshold, enabling the unprecedented two-electron transfer.

Counting DNA molecules on a microchannel surface for quantitative analysis

Microscopic visualization of DNA molecules is a simple, intuitive, and powerful method. Nonetheless, DNA-molecule quantification methods that employ microscopic visualization have not been reported so far. In this study, a new quantitative approach is presented that enables the counting of individual DNA molecules that have been rendered visible by fluorescence microscopy. Toward this, a microfluidic device was employed that directed DNA molecules into microchannels and deposited the molecules onto a positively charged surface. This microfluidic device had a vertically tapered channel inlet structure that prevented the accumulation of excess DNA molecules in the channel inlet while creating a tapering flow, thereby ensuring the even distribution of the DNA molecules in the microchannels. The channel heights and the density of positive charges on the surface were optimized for analysis. The linearity of this method with respect to the determination of the concentration of DNA in solutions was subsequently determined. The limit of detection was 0.48 fg/μL, which corresponds to 64 molecules of 7.25 kbp DNA in 1 μL of sample. This quantitative approach was finally used to count two types of plasmids co-transformed in an E. coli cell; a measurement that is typically considered challenging with gel electrophoresis.

Evaluating the role of salts on emulsion properties during water-based enhanced oil recovery: Ion type, concentration, and water content

Potential determining ions (SO42−, Mg2+, Na, and Ca2+) positively affect oil recovery. These ions can cause changes in the oil and water system due to their ionic radius and proper charge density. Besides the type of ions, the concentration of these ions is also important. In order to maximize oil recovery, the concentration of these active ions should be at a level that pulls the polar components of the oil towards the oil–water interface and causes the interfacial tension to decrease, resulting in a decrease in capillary force and an increase in oil recovery. In some cases, the presence of various ions in the formation water or injection water provides the conditions for the formation and stability of the emulsion. Emulsion formation sometimes reduces production and sometimes improves production from oil reservoirs. Therefore, it is imperative to study the effects of ions on the formation, stability, and viscosity of emulsions. Regarding the emulsion stability in the presence of different ions, there are high uncertainties, and there is no uniform opinion on this matter. In this study, MgCl2, CaCl2, NaCl, and Na2SO4 were used to investigate emulsion properties. Droplet size and viscosity were measured using an optical microscope and a rolling ball viscometer, respectively, in order to determine emulsion stability. The results have shown that salts with higher positive charge density, such as MgCl2 and CaCl2 can significantly reduce the size of emulsion droplets and increase emulsion stability. Moreover, the presence of divalent anions such as sulfate reduces the amount of asphaltene at the interface between oil and water, thereby reducing the stability of the emulsion. In the order of MgCl2 > CaCl2 > Na2SO4 > NaCl, salts decreased the droplet size and increased the emulsion stability. The viscosity of the emulsion also showed a similar trend, as the average particle size decreases, the viscosity of the emulsion increases. Based on the results, the size of the emulsion droplets decreases up to a certain concentration and then increases. In the case of all salts, this concentration was equal to 10,000 ppm. The viscosity of the emulsion shows an increasing trend up to the concentration of 10,000 ppm, and after this concentration, it shows a decreasing trend. Salt-in and salt-out effects are responsible for the reduction and increase in droplet size. This study can provide insight into the effect of different ions on the stability and viscosity of the emulsion, as well as the design of the injection fluid for the enhanced oil recovery process.

Impact of hydroxyl aluminum speciation on dewaterability and pollutants release of dredged sludge using polymeric aluminum chloride

Flocculation conditioning is a common pretreatment step for dredged sludge dewatering, while various pollutants in sludge might release into the residual water during flocculation conditioning and dewatering process, leading to secondary pollution. In this study, polymeric aluminum chloride (PAC) with different alkalinity was used as conditioners to enhance the dewaterability of dredged sludge in Baiyangdian Lake, and effects of hydroxyl aluminum speciation on dewatering performance and release of pollutants of dredged sludge were investigated. The results showed that the surface positive charge density of the mediumly polymeric hydroxyl aluminum (Alb) and highly polymeric hydroxyl aluminum (Alc) was higher, and the produced flocs were more compact, the abundant pore structure in flocs enhanced the water transport capacity and dewatering performance. Correlation analysis results showed that the release of heavy metals in residual water was mainly related to Ala, and the release of high molecular weight organic matter (aromatic protein), nitrogen and phosphorus was related to Alb, while Alc helped reduce pollutions in residual water. Alc showed better performance in improving dredged sludge dewaterability, and reduce the release of pollutants. This study provides an optimized strategy of flocculants for dredged sludge treatment based on aluminum speciation control.

Effect of Substituents on the Homopolymerization Activity of Methyl Alkyl Diallyl Ammonium Chloride.

Among nitrogen-containing cationic electrolytes, diallyl quaternary ammonium salt is a typical monomer with the highest positive charge density, which has attracted the most attention, especially in the research on homopolymers and copolymers of dimethyl diallyl ammonium chloride (DMDAAC), which occupy a very unique and important position. In order to improve the lipophilicity of substituted diallyl ammonium chloride monomers under the premise of high cationic charge density, the simplest, most direct, and most efficient structure design strategy was selected in this paper. Only one of the substituents on DMDAAC quaternary ammonium nitrogen was modified by alkyl; the substituents were propyl and amyl groups, and their corresponding monomers were methyl propyl diallyl ammonium chloride (MPDAAC) and methyl amyl diallyl ammonium chloride (MADAAC), respectively. The effect of substituent structure on the homopolymerization activity of methyl alkyl diallyl ammonium chloride was illustrated by quantum chemical calculation and homopolymerization rate determination experiments via ammonium persulfate (APS) as the initiator system. The results of quantum chemistry simulation showed that, with the finite increase in substituted alkyl chain length, the numerical values of the bond length and the charge distribution of methyl alkyl diallyl ammonium chloride monomer changed little, with the activation energy of the reactions in the following order: DMDAAC < MPDAAC < MADAAC. The polymerization activities measured by the dilatometer method were in the order DMDAAC > MPDAAC > MADAAC. The activation energies Ea of homopolymerization were 96.70 kJ/mol, 97.25 kJ/mol, and 100.23 kJ/mol, and the rate equation of homopolymerization of each monomer was obtained. After analyzing and comparing these results, it could be easily found that the electronic effect of substituent was not obvious, whereas the effect of the steric hindrance was dominant. The above studies have laid a good foundation for an understanding of the polymerization activity of methyl alkyl diallyl ammonium chloride monomers and the possibility of preparation and application of these polymers with high molecular weight.

Quaternary ammonium engineered polyamide membrane with high positive charge density for efficient Li+/Mg2+separation

The efficient separation of Li+/Mg2+ is the key to lithium extraction from salt lake brine. Herein, a multi-amino quaternary ammonium salt (3,5-dimethylhydrazide-benzyl trimethyl ammonium bromide, DHTAB) was designed and synthesized to modify pristine polyamide (PA) nanofiltration membranes. DHTAB was grafted on the surface of the PA nanofiltration membrane to construct a positively selective layer for Li+/Mg2+ separation. The introduction of DHTAB increased the membrane surface charge density to +5.16 mC m−2, which was nearly three times that of the pristine PA membrane. The increased charge density of the modified membrane led to a stronger Donnan exclusion for Mg2+, and accordingly a high MgCl2 rejection of 99.2%. The modified membranes exhibited a high Li+/Mg2+ separation factor of up to 60.1, when applied for MgCl2 and LiCl binary solution, which exceeded all known PA-based nanofiltration membranes.

Radio Emission of Pulsars. I. Slow Tearing of a Quantizing Magnetic Field

The pulsed radio emission of rotating neutron stars is connected to slow tearing instabilities feeding off an inhomogeneous twist profile within the open circuit. This paper considers the stability of a weakly sheared, quantizing magnetic field in which the current is supported by a relativistic particle flow. The electromagnetic field is almost perfectly force free, and particles are confined to the lowest Landau state, experiencing no appreciable curvature drift. In a charge-neutral plasma, we find multiple branches of slowly growing tearing modes, relativistic analogs of the double-tearing mode, with peak growth rate . Here, B z is the strong (nearly potential) guide magnetic field, J z the field-aligned current density, and is the mode wavenumber normalized by the current gradient scale. These modes are overstable when the plasma carries a net charge, with the real frequency proportional to the imbalance in the densities of positive and negative charges. An isolated current sheet thinner than the skin depth supports localized tearing modes with growth rate scaling as (sheet thickness/skin depth)−1/2. In a pulsar, the peak growth rate is comparable to the angular frequency of rotation, , slow compared with the longitudinal oscillations of particles and fields in a polar gap. The tearing modes experience azimuthal drift reminiscent of subpulse drift and are a promising driver of pulse-to-pulse flux variations. A companion paper demonstrates a Cerenkov-like instability of current-carrying Alfvén waves in thin current sheets with relativistic particle flow and proposes coherent curvature emission by these waves as a source of pulsar radio emission.

Antimicrobial activity of lactoferrin-chitosan-gellan nanoparticles and their influence on strawberry preservation

Lactoferrin (L), chitosan (C) and gellan (G) nanoparticles were produced by electrostatic complexation, aiming to enhance the antimicrobial characteristics of these compounds. Binary complexes (lactoferrin-gellan and chitosan-gellan) and ternary complexes (lactoferrin-chitosan-gellan) were studied in eight different proportions of biopolymers. The antimicrobial activity of nanoparticles against S. aureus was compared with that of pure biopolymers and related to nanoparticle size, charge density and morphology. Those with a 4.5L:4.5C:1G ratio presented the highest positive charge density (+57.90 ± 1.50) mV and smaller hydrodynamic diameter (53.53 ± 2.06) nm, which resulted in the highest antimicrobial action (minimum inhibitory concentration of 0.0117 mg/ml). When applied to a coating of fresh strawberries, the nanoparticles were effective in preserving their physicochemical properties, especially in the presence of carboxymethylcellulose that enhanced the adhesion of particles to the fruits. In this study, the antimicrobial action of nanoparticles was better than that of lactoferrin and pure chitosan alone, proving that the antimicrobial properties of such biopolymers were enhanced due to aggregation at the nanoscale. The nanoparticles produced have outstanding application potential as natural food preservers.

Investigation of transport properties of perovskite single crystals by pulsed and DC bias transient current technique

Time-of-flight (ToF) transient current method is an important technique to study the transport characteristics of semiconductors. Here, both the direct current (DC) and pulsed bias ToF transient current method are employed to investigate the transport properties and electric field distribution inside the MAPbI3 single crystal detector. Owing to the almost homogeneous electric field built inside the detector during pulsed bias ToF measurement, the free hole mobility can be directly calculated to be about 22 cm2⋅V−1⋅s−1, and the hole lifetime is around 6.5 μs–17.5 μs. Hence, the mobility-lifetime product can be derived to be 1.4 × 10−4 cm2⋅V−1–3.9 × 10−4 cm2⋅V−1. The transit time measured under the DC bias deviates with increasing voltage compared with that under the pulsed bias, which arises mainly from the inhomogeneous electric field distribution inside the perovskite. The positive space charge density can then be deduced to increase from 3.1 × 1010 cm−3 to 6.89 × 1010 cm−3 in a bias range of 50 V–150 V. The ToF measurement can provide us with a facile way to accurately measure the transport properties of the perovskite single crystals, and is also helpful in obtaining a rough picture of the internal electric field distribution.

Potential risk resulting from the influence of static magnetic field upon living organisms. Numerically simulated effects of the static magnetic field upon simple alkanols

Background: Recognising effects of static magnetic field (SMF) of varying flux density on flora and fauna is attempted. For this purpose, the influence of static magnetic field upon molecules of lower alkanols i.e. methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, S-butan-2-ol, isobutanol and tert-butanol is studied. Methods: Computations of the effect of real SMF 0.0, 0.1, 1, 10 and 100 AFU (Arbitrary Field Unit; here 1AFU &amp;gt; 1000 T) flux density were performed in silico (computer vacuum), involving advanced computational methods. Results: SMF polarises molecules depending on applied flux density, but it neither ionises nor breaks valence bonds. Some irregularities in the changes of positive and negative charge densities and bond lengths provide evidence that molecules slightly change their initially fixed positions with respect to the force lines of the magnetic field. Length of some bonds and bond angles change with an increase in the applied flux density, providing, in some cases, polar interactions between atoms through space. Conclusions: Since SMF produced and increase in the negative charge density at the oxygen atom of the hydroxyl group and elongated the –O-H bond length, these results show that SMF facilitates metabolism of the alkanols.

A new guard ring for ionizing radiation tolerance enhancement in single-photon avalanche diodes

A new guard ring is studied to improve radiation tolerance of single-photon avalanche diodes (SPAD) designed in 180 nm high voltage Complementary Metal-Oxide-Semiconductor (CMOS) technology. The radiation tolerance enhancement is obtained due to the reduction of the electric field inside Shallow Trench Isolation (STI), which reduces radiation-induced positive oxide charge density inside the STI by almost one order of magnitude. TCAD simulations show that, after 1 Mrad (SiO2) of X-ray radiation with a cathode voltage of 24.4 V, the increase in dark count rate at room temperature compared to pre-irradiation is 1438 counts per second (cps) and 311 cps for the conventional structure and new structure respectively, which shows a 78.3 % decrease in DCR increment for the new structure as compared to the conventional one. Moreover, the fill factor and photon detection probability of the new structure decreases by 0.3 % and 6 % compared to the conventional structure, which is negligible.

Effect of ion partitioning on an oscillatory electro-osmotic flow on solute transport process of fractional Jeffrey fluid through polyelectrolyte-coated nanopore with reversible wall reaction

The ion-partitioning effects on solute transport phenomena of time-periodic electro-osmotic flow in fractional Jeffrey fluid are investigated through a polyelectrolyte layer (PEL)-coated conical nanopore within a reactive wall whose ends are connected with two large reservoirs. By considering the ion-partitioning effects, analytical solutions for the induced potential and the axial velocity are presented, respectively, from the modified Poisson–Boltzmann equation and the Cauchy momentum equation with the proper constitutive equation of the fractional Jeffrey fluid model in the exterior and interior of the PEL. The analytic solution of the convection–diffusion for solute transport is established in the entire domain. The influence of the oscillating Reynolds number Rew, permittivity ratio εr between two mediums, relaxation time λ1ω, retardation time λ2ω, phase partitioning coefficient σp, PEL fixed charge density qfix, Debye–Hückel parameter κa, and softness parameter λs are investigated in this study. Asymptotic solution for the axial velocity was also presented for low-oscillating Reynolds numbers and validated. The maximum axial velocity occurs when the permittivity between the PEL and electrolyte is the same for all models. The volumetric flow rate decreases with the increase in the PEL thickness, positive PEL charge density, and softness parameter in our study. The volume flow rate of the Newtonian fluid increased 24.07% for Maxwell fluid (λ1ω=5, α = 1) and 11.56% for Jeffrey fluid (λ1ω=5, λ1ω=1, α = 1, and β=0.5), when κa=25, Rew = 10, qfix = 5, d = 0.2, εr=0.6, and λs=1.0. The mass transport rate increases with relaxation time, tidal displacement, and permittivity ratio between these layers.

Uniform cobalt nanoparticles embedded in nitrogen-doped graphene with abundant defects as high-performance bifunctional electrocatalyst in overall water splitting

Co nanoparticles with uniform size (about 5 nm) embedded in N-doped graphene (Co-NG) were explored in this work. The introduction of a second carbon source of citric acid during synthesis prevented the Co atoms from growing up, thus regulating the size of the cobalt nanoparticles. N atoms in N-doped graphene had more lone-pair electrons, making it easier to capture electrons from hydrated ions, and facilitating the dynamics procedure of HER. Furthermore, N dopant rendered larger positive charge density on the adjacent carbon atoms, which was conducive to OER and HER. At 10 mA cm−2 of the current density, the Co-NG/CC catalyst's overvoltage of HER was 78 mV, approaching that of 20% Pt/C (59 mV), an efficient precious metal electrocatalyst for HER, while its overvoltage of OER was about 225 mV, 12.5% lower than that of RuO2 (257 mV, a common precious metal oxide OER electrocatalyst). In addition, this Co-NG/CC composite bifunctional catalyst displayed good electrochemical stability in alkali solution and might be designed as a dual-function catalyst in the application of overall water splitting. The cell voltage of Co-NG/CC//Co-NG/CC was only 1.66 V, approaching to that of full precious metal cell of Pt/C//RuO2 (1.52 V), and revealing the good commercial application prospects of this composite bifunctional catalyst.