Increasing Mass Loading Research Articles

Triazole-enabled small TEMPO cathodes for lithium-organic batteries

The use of redox-active organic compounds to make rechargeable batteries is a promising strategy for future energy storage especially from a resource and environmental sustainability point of view. While many organic structures have been identified as potential electroactive materials, their direct application in solid-state energy storage is limited. This is due to their high solubility in common organic electrolytes, resulting in poor long-term battery performance. In this work, we overcome this significant problem by synthesizing very low soluble nitroxide radicals with theoretical capacities of 111–131 mAh g−1, equal to or higher than most commonly used nitroxide radical polymers. These new structures consist of TEMPO (i.e. 2,2,6,6-tetramethylpiperidinyl-1-oxy) radicals and triazole ring linkages synthesized by the copper-catalyzed azide-alkyne cycloaddition (CuAAC) ‘click’ reaction. Analysis of electrode morphology and electrochemical performance at increasing mass loading of the nitroxide radicals demonstrate the importance of lower solubility, preventing the shuttle effect observed for common organic electrode materials. The electrodes with the content of active materials up to 80 wt% can still maintain a good interaction with the carbon and conductivity throughout the electrode and deliver a capacity greater than 60 mAh g−1 over 200 cycles.

Ionic strength controls long-term cell-surface interactions – A QCM-D study of S. cerevisiae adhesion, retention and detachment

Understanding microbial adhesion and retention is crucial for controlling many processes, including biofilm formation, antimicrobial therapy as well as cell sorting and cell detection platforms. Cell detachment is inextricably linked to cell adhesion and retention and plays an important part in the mechanisms involved in these processes. Physico-chemical and biological forces play a crucial role in microbial adhesion interactions and altering the medium ionic strength offers a potential means for modulating these interactions. Real-time studies on the effect of ionic strength on microbial adhesion are often limited to short-term bacterial adhesion. Therefore, there is a need, not only for long-term bacterial adhesion studies, but also for similar studies focusing on eukaryotic microbes, such as yeast. Hereby, we monitored, in real-time, S. cerevisiae adhesion on gold and silica as examples of surfaces with different surface charge properties to disclose long-term adhesion, retention and detachment as a function of ionic strength using quartz crystal microbalance with dissipation monitoring. Our results show that short- and long-term cell adhesion levels in terms of mass-loading increase with increasing ionic strength, while cells dispersed in a medium of higher ionic strength experience longer retention and detachment times. The positive correlation between the cell zeta potential and ionic strength suggests that zeta potential plays a role on cell retention and detachment. These trends are similar for measurements on silica and gold, with shorter retention and detachment times for silica due to strong short-range repulsions originating from a high electron-donicity. Furthermore, the results are comparable with measurements in standard yeast culture medium, implying that the overall effect of ionic strength applies for cells in nutrient-rich and nutrient-deficient media.

Architecture Transformations of Ultrahigh Areal Capacity Air Cathodes for Lithium‐Oxygen Batteries

AbstractLithium‐oxygen (Li−O2) batteries have the highest known theoretical energy density but are still not practical for use in most applications. A key aspect that has been largely overlooked in the field is how to improve the reversible areal capacity of the air cathode to a competitive level (>5–10 mAh cm−2). For carbon‐based air cathodes, increase of areal capacity requires a corresponding increase of carbon mass loading. As a result, the electrode thickness also increases which impedes the mass transport of Li ions and O2 needed for battery reactions. It is therefore imperative to investigate not only the air cathode composition, but also its dimensional architecture, for the effective function of high areal capacity Li−O2 batteries. Herein, we present the use of several representative additives of carbon‐based nanomaterials, including carbon black, two different diameters of multi‐walled carbon nanotubes, and graphene materials from two sources, into a high mass loading (10 mg cm−2), ultrathick (∼100 μm) air cathode architectural platform matrix based on dry‐compressed holey graphene. The performances of these all‐carbon composite air cathodes differ from that of the neat holey graphene, but not by a simple addition or subtraction effect. In addition, the additive effects to full discharge and curtailed cycling experiments are significantly different. The presented results strongly suggest that the architectural volume expandability is critical for the full discharge properties. However, the cycling performance depends more upon the resilience of the air cathode architecture (“breathability”), which does not necessarily correlate with its expandability.

Surface acoustic wave ammonia sensor based on SiO2–SnO2 composite film operated at room temperature

Sensitive thin film layers of SnO2, SiO2 and SiO2–SnO2 were deposited on a surface acoustic wave resonator using sol-gel method and spin coating techniques. Their ammonia-sensing performance operated at room temperature was characterized and their sensing mechanisms were comprehensively studied. When exposed to ammonia, the sensors made of SnO2 and SiO2–SnO2 films exhibit positive frequency shifts, whereas the SiO2 film sensors exhibit a negative frequency shift. The positive frequency shift is related to the dehydration and condensation of hydroxyl groups, which makes the films stiffer and lighter. The negative frequency shift is mainly caused by the increase of mass loading due to the adsorption of ammonia. The gas sensor based on SiO2–SnO2 film shows a positive frequency shift of 631 Hz when it is exposed to ammonia with a low concentration of 3 ppm, and it also shows good repeatability and stability, as well as a good selectivity to ammonia compared with gases of C6H14, C2H5OH, C3H6O, CO, H2, NO2, and CH4.

Alternately Dipping Method to Prepare Graphene Fiber Electrodes for Ultra-high-Capacitance Fiber Supercapacitors.

SummaryFlexible fiber supercapacitors are promising candidate for power supply of wearable electronics. Fabrication of high-performance fibers is in progress yet challenging. The currently available graphene fibers made from wet-spinning or electro-deposition technologies are far away from practical applications due to their unsatisfactory capacitance. Here we report a facile alternately dipping (AD) method to coat graphene on wire-like substrates. The excellent mechanical properties of the substrate with greatly diverse choices can be carried over to the fiber supercapacitors. Under such guideline, the graphene fiber with a titanium core made by our AD method (AD:Ti@RGO) shows an ultra-high specific capacitance of up to 1,722.1 mF cm−2, which is ∼1,000 times that of wet-spinning- and electro-deposition-fabricated neat graphene fibers and presents the highest specific capacitance to date. With excellent mechanical properties and striking electrochemical performances, the AD:Ti@RGO-based supercapacitors light the path to the next-generation technologies for wearable devices.

Matrix-specific mechanism of Fe ion release from laser-generated 3D-printable nanoparticle-polymer composites and their protein adsorption properties

Nanocomposites have been widely applied in medical device fabrication and tissue-engineering applications. In this context, the release of metal ions as well as protein adsorption capacity are hypothesized to be two key processes directing nanocomposite-cell interactions. The objective of this study is to understand the polymer-matrix effects on ion release kinetics and their relations with protein adsorption. Laser ablation in macromolecule solutions was employed for synthesizing Au and Fe nanoparticle-loaded nanocomposites based on thermoplastic polyurethane (TPU) and alginate. Confocal microscopy revealed a three-dimensional homogeneous dispersion of laser-generated nanoparticles in the polymer. The physicochemical properties revealed a pronounced dependence upon embedding of Fe and Au nanoparticles in both polymer matrices. Interestingly, the total Fe ion concentration released from alginate gels under static conditions decreased with increasing mass loadings, a phenomenon only found in the Fe-alginate system and not in the Cu/Zn-alginate and Fe-TPU control system (where the effects were proportioonal to the nanoparticle load). A detailed mechanistic examination of iron the ion release process revealed that it is probably not the redox potential of metals and diffusion of metal ions alone, but also the solubility of nano-metal oxides and affinity of metal ions for alginate that lead to the special release behaviors of iron ions from alginate gels. The amount of adsorbed bovine serum albumin (BSA) and collagen I on the surface of both the alginate and TPU composites was significantly increased in contrast to the unloaded control polymers and could be correlated with the concentration of released Fe ions and the porosity of composites, but was independent of the global surface charge. Interestingly, these effects were already highly pronounced at minute loadings with Fe nanoparticles down to 200 ppm. Moreover, the laser-generated Fe or Au nanoparticle-loaded alginate composites were shown to be a suitable bioink for 3D printing. These findings are potentially relevant for ion-sensitive bio-responses in cell differentiation, endothelisation, vascularisation, or wound healing.

Evaporating droplets in shear turbulence

This paper investigates droplets that evaporate and cluster in shear turbulence with direct numerical simulations. The flows are statistically stationary and homogeneous, which reduces the physical complexity and simplifies the statistical analysis. The mass loadings are about 0.1, the Stokes numbers are about 1, and the Taylor-scale Reynolds numbers are about 60. The simulations show that the clusters are anisotropic and inclined toward the flow direction on large scales, but isotropic on small scales. When the mass loading increases, the clusters contain more droplets, but their size remains unchanged, and the droplets in clusters experience higher vapor mass fractions. When the Stokes number increases, the clusters contain fewer droplets and become larger, and the droplets in clusters experience lower vapor mass fractions. When the Reynolds number increases, the clusters contain more, smaller droplets and become smaller, and the inclination angles of the clusters change.

High areal capacitance of manganese oxide electrodes with cerium as rare earth modification

Manganese oxides have attracted wide attention as promising electrode materials for high-energy density supercapacitors. However, the electrochemical performance of the manganese oxide materials deteriorates considerably with the increase in mass loading due to their moderate electronic and ionic conductivities. This phenomenon leads to low areal capacitance, which limits the practical application of these materials. Herein, we perform a potentiostatic electrodeposition of manganese oxides with Ce as rare earth (RE) modification on a nickel (Ni) foam substrate to achieve high areal capacitance. Under optimum conditions, manganese oxide nanosheets are axially grown on Ni foam to form a hierarchically porous network nanostructure, which ensures facile ionic and electric transport. The Ce-modified manganese oxide with the Mn:Ce molar ratio of 1:0.1 yields an outstanding areal capacitance of 3.67 F cm–2 at 2 mA cm–2 and a good rate capability compared with the capacitance of 2.59 F cm–2 at 2 mA cm–2 of pure manganese oxide without the addition of Ce. This result verifies the importance of Ce modification to manganese oxides. Our results suggest the important role played by the RE element Ce in enhancing the electrochemical performance of high areal capacitance manganese oxide electrodes, which is essential to bringing them one step toward further practical applications.

Ultrahigh “Relative Energy Density” and Mass Loading of Carbon Cloth Anodes for K-Ion Batteries

Mass loading and potential plateau are the two most important issues of potassium (K)-ion batteries (KIBs), but they have long been ignored in previous studies. Herein, we report a simple and scala...

Effects of turbulence modulation and gravity on particle collision statistics

Dynamics of inertial particles in homogeneous isotropic turbulence is investigated by means of numerical simulations that incorporate the effect of two-way interphase momentum transfer. The continuous phase is solved in the Eulerian approach employing Direct Numerical Simulations (DNS). The dispersed phase is treated using the Lagrangian approach along with the point-particle assumption. The main focus is on computing collision statistics of inertial particles relevant to cloud droplets in typical atmospheric conditions. The vast majority of previous DNS were performed assuming one-way momentum coupling between continuous and dispersed phases. Such simplified approach is adequate only for dilute systems with relatively low mass loading. In this study we investigate the effect of two-way momentum coupling on the kinematic and dynamic collision statistics of the dispersed phase. A number of simulations have been performed at different droplet radii (inertia), mass loading, viscosity and energy dissipation rate. To assess the accuracy of numerical approach the coupling force (exerted by particles on the fluid) was computed using two different techniques, namely particle in cell and projection onto neighboring node. To address the effect of gravity, the simulations have been carried out simultaneously both with and without gravitational acceleration. It has been found that the effect of two-way coupling is significant both for droplet clustering and the radial relative velocity. It turns out that the collision kernel is more sensitive to the particle mass loading when the gravitational acceleration is considered. The collision kernel of settling droplets increases as the droplet mass loading increases. This is direct consequence of larger radial relative velocity. For non-settling droplets the effect of mass loading is opposite, namely, we observe a minor reduction of the collision kernel as the number of droplets increases.

Investigation of the Horizontal Motion of Particle-Laden Jets

Particle-laden jet flows can be observed in many industrial applications. In this investigation, the horizontal motion of particle laden jets is simulated using the Eulerian–Lagrangian framework. The two-way coupling is applied to the model to simulate the interaction between discrete and continuum phase. In order to track the continuum phase, a passive scalar equation is added to the solver. Eddy Life Time (ELT) is employed as a dispersion model. The influences of different non-dimensional parameters, such as Stokes number, Jet Reynolds number and mass loading ratio on the flow characteristics, are studied. The results of the simulations are verified with the available experimental data. It is revealed that more gravitational force is exerted on the jet as a result of the increase in mass loading, which deflects it more. Moreover, with an increase in the Reynolds number, the speed of the jet rises, and consequently, the gravitational force becomes less capable of deviating the jet. In addition, it is observed that by increasing the Stokes number, the particles leave the jet at higher speed, which causes a lower deviation of the jet.

Similar “relay race” capacitance behaviors of folded graphene films based high-performance supercapacitors

Graphene film has a great planar electron transport characteristic, yet its vertical electron transport efficiency is limited due to the two-dimensional stacked structure, which restricts the wide implementation of graphene-based films in energy storage field, such as supercapacitors (SCs). Herein, we present a novel folding strategy to tackle this issue and enable preparation of high mass loading graphene film possessing high-performance. Folded reduced graphene oxide (F-rGO) films via low-temperature thermal reduction show the folded paper-like structure and an interesting electrochemical law. Briefly, by combining the capacitance performance of different fold films, the resulting films exhibit a capacitance retention behavior of similar “relay race”, rendering that their gravimetric capacitance always maintain high level value (>180 F g−1) at the range of 2–9 mg cm−2, and the volumetric capacitance can achieve ~232 F cm−3 even at 11.3 mg cm−2. Meanwhile, their areal capacitance also exhibits a relay-like and linear growth with increasing mass loading and eventually achieve ~3400 mF cm−2 at 17 mg cm−2. In addition, flexible all-solid state SCs assembled by the F-rGO films also present excellent electrochemical and structural stability under bending states. Therefore, we believe that folding technique is a meaningful way to produce high-performance graphene based electrodes.

Non-monotonic effect of mass loading on turbulence modulations in particle-laden channel flow

The effect of mass loading on turbulence modulation in channel flows is investigated in two-way coupled direct numerical simulations with the Lagrangian point-particle method. We carried out the simulations of turbulent channel flows at Reτ = 180, and the particle mass loading ranges from 0 to 0.96 with a fixed Stokes number St = 30. The statistics show that the intensity of the streamwise velocity fluctuation augmented non-monotonically with the increase in mass loading. The maximum enhancement of the streamwise turbulence intensity observed at a mass-loading of ϕm = 0.75 is 60% greater than that of the unladen flow. However, the velocity fluctuations in the spanwise and wall-normal direction as well as the Reynolds shear stress are attenuated monotonically with mass loading. To better interpret the non-monotonic effect of mass loading on the streamwise turbulence intensity, we further examined the near-wall vortices and streaks and proposed two competitive mechanisms. First, we found that the near-wall vortices become fewer and weaker and the spacing between streaks become wider as ϕm increases, which results in the damping effect on the fluctuation of the streamwise velocity. Second, the vortex structures and the streaks become more organized and straightly aligned in the streamwise direction with an increase in the streak strength, which enhances the streamwise velocity fluctuations. In addition, we observed a non-monotonic change in turbulent kinetic energy transfer between particle and fluid phases. The statistics of energy budgets show that particles extract energy from the fluid phase at ϕm < 0.6 but transfers energy back to the fluid phase at ϕm > 0.75 in the stream-wise direction.

Electrode Design for High-Performance Sodium-Ion Batteries: Coupling Nanorod-Assembled Na3V2(PO4)3@C Microspheres with a 3D Conductive Charge Transport Network.

As one of the most promising cathodes for sodium-ion batteries, the polyanionic compounds still suffer from unsatisfactory capacity and rate performance resulting from poor electron conductivity. Furthermore, the charge-transfer kinetics, especially for Na+, becomes limiting as the mass loading increases. Herein, a robust free-standing electrode coupling optimal porous Na3V2(PO4)3@C microspheres with a bicontinuous charge transport network is designed and prepared by a simple casting method. In the design, the optimal porous carbon-coated microspheres, composed of some continuous nanorods, along with interwoven carbon nanofiber networks offer efficient electron transport and facile ion diffusion. Such an elaborate design enables impressive electron/ion conductivity, contributing to remarkable rate performance (116.1 mA h g-1 at 0.2 C; 96 mA h g-1 at 30 C) and outstanding cycling stability (90% capacity retention in 500 cycles at 1 C; 80% capacity retention in 5000 cycles at 10 C), which has surpassed other similar Na3V2(PO4)3-based free-standing electrodes as reported. More importantly, when mass loading extends to 8 mg cm-2, an excellent capacity retention of 75% at 10 C can be obtained. The research offers a new avenue into the rational design of porous microspheres electrode with high conductive charge transport network, indicating its superiority in practical applications.

Efficient 3D Printed Pseudocapacitive Electrodes with Ultrahigh MnO2 Loading

Retaining sound electrochemical performance of electrodes at high mass loading holds significant importance to energy storage. Pseudocapacitive materials such as manganese oxide (MnO2) deposited on current collectors have achieved outstanding gravimetric capacitances, sometimes even close to their theoretical values. Yet, this is only achievable with very small mass loading of active material typically less than 1 mg cm-2. Increasing mass loading often leads to drastic decay of capacitive performance due to sluggish ion diffusion in bulk material. In this talk, I will demonstrate a 3D printed macroporous graphene aerogel electrode with MnO2 loading of 182.2 mg cm-2, which achieves a record-high areal capacitance of 44.13 F cm-2. The engineered porous structure allows efficient ion diffusion and therefore enables the ultrahigh mass loading of pseudocapacitive materials without sacrificing their gravimetric and volumetric capacitive performance. Most importantly, this 3D printed graphene aerogel/MnO2 electrode can simultaneously achieve excellent capacitance normalized to area, gravimetry, and volume, which is the trade-off for most electrodes. This work successfully validates the feasibility of printing practical pseudocapacitive electrodes, which might innovate the conventional layer-by-layer stacking fabrication process of commercial supercapacitors. Figure 1

Bucky-Si-Bucky Sandwiched Structured Anode for Li-Ion Battery

Silicon anodes have been of great interest due to their higher theoretical capacity (4200 mAh/g) compared to traditional graphite electrodes (~372 mAh/g). Although Si has a higher capacity, its full potential has not yet been realized due to pulverization of Si anode upon lithiation. Conventionally, Si anodes are made by casting a slurry consisting of Si powder, conductive carbon additives, and a binder on a Cu foil. In such anodes, pulverization of Si particles leads to film delamination from Cu foil ensuing in battery failure. To overcome this challenge, we developed a new sandwich-structured anode by encapsulating ~100 nm Si nanoparticles in between two porous carbon nanotube buckypapers. The buckypaper is a conductive porous structure, which can incorporate active material better than Cu foil facilitating increased mass loading. More importantly, this sandwich-structured anode provides improved electrical contact even under repeated pulverization of Si nanoparticles leading to higher cyclability. We were able to achieve capacities as high as ~700-1200 mAh/g with a stable performance for >100 cycles.

CuO nanorods growth on folded Cu foil as integrated electrodes with high areal capacity for flexible Li-ion batteries

Although the conventional slurry-coated electrodes are successful in various batteries, they do not suit for flexible electrodes based energy storage because the active materials tend to detach from the current collector during bending. Besides, the electrochemical performance of slurry-coated electrodes always declines dramatically with increasing mass loading, resulting in limited areal capacity (∼3.5 mA h cm−2 or less). Herein, we develop a series of CuO nanorods/folded Cu foil integrated electrodes with high mass loading and areal capacity for flexible energy storage. CuO nanorods grow directly on Cu foil, not only restraining the exfoliation of CuO from Cu substrate under bending but also facilitating electron transport. By using a folding design, the integrated electrode (four folds) can reach CuO loading of 15.2 mg cm−2 and deliver a high areal capacity of 13.95 mA h cm−2 at the first discharge. Using these CuO/Cu integrated electrodes as anodes, we construct flexible Li-ion full cells, exhibiting excellent electrochemical performance and superior mechanical strength of anodes.

S-doping coupled with pore-structure modulation to conducting carbon black: Toward high mass loading electrical double-layer capacitor

The conductive carbon black (CB) was modified by the pore-structure modulation and S doping in the presence of pore-modulation agent and S dopant via the one-step calcination methodology, resulting in the S-doped and pore-structure modified CB (labeled as SPCB). The conductivity and contact angle tests prove that the function of S doping can not only increase the electrical conductivity but also enhance the hydrophilicity. As electrode materials for symmetric electrical double-layer capacitor (EDLC), the influence of different mass loading of the electrode on the capacitive behavior is investigated. The areal mass loading of active materials for each electrode in the symmetric EDLC can reach up to 10 mg cm−2, comparable to the values of commercial devices. Without obvious sacrifice of the gravimetric capacitance is observed with the increase of mass loading, illustrating the small electrolyte ion transport resistance in electrode material and quick charge transfer property as well as the great compatibility for the gravimetric, areal and total capacitances. Additionally, the symmetric EDLC configured with SPCB affords the larger capacitance, better rate capability and higher capacitance retention as compared to the commercial activated carbon.

Study of erosion prediction of turbulent gas-solid flow in plugged tees via CFD-DEM

In many industrial applications, sand erosion wear is the main cause of equipment failure, particularly in the transferring pipeline fittings. In order to reduce the adverse consequences of erosion in bends, in this study the potential usage of plugged tees instead of standard elbows under a wide range of flow conditions is examined. A computational fluid dynamics (CFD) model coupled with discrete element method (DEM) was used and the particle-laden flows with different fluid velocities in the corresponding geometries carrying various entrained particle mass loadings were simulated. The reliability of selected turbulence models as well as rebound and erosion models were verified by comparing the model predictions with the available experimental data. The final simulation model included the E/CRC erosion model, and the Grant and Tabakoff rebound model. The DEM used in the computational model includes the effects of particles rotation and collisions between the particles. The study also considered the effect of modifications of the plugged length of the tee geometries. The simulation results indicated that, as the particle mass loading increases, the effectiveness of plugged tee compared to the standard elbow increases. Moreover, although increasing the plugged length will generally reduce the erosion rate due to the cushioning effect, the rate of reduction depends on mass loading.

Mass-loading independent electrocatalyst with high performance for oxygen reduction reaction and Zn-air battery based on Co-N-codoped carbon nanotube assembled microspheres

Although carbon materials have shown large potential as efficient electrocatalysts for oxygen reduction reaction (ORR), their practical performance with high energy density and power density is difficult to maintain under high mass-loading due to the compact restacking that seriously hinders mass/charge diffusion. To overcome this issue, we demonstrate the design and synthesis of hierarchical Co-N-codoped carbon nanotube hollow microspheres (CNT HMSs) with high disperse, large surface area and uniform mesopores, which effectively guarantees the high electrochemical activity and stability towards ORR even under high mass-loading. As a result, the power density of Zn-air battery based on CNT HMS gradually enhances from 52.8 to 183.8 mW cm−2 with a good linear relationship when the mass-loading increases from 1.5 (traditional used for most reported works) to 6.0 mg cm−2, indicating a well-preserved catalytic activity with high mass-loading. In addition, the long-term stability (10 h) test illustrates that monodisperse morphology and uniform size distribution of CNT HMS have been well maintained, while the referent carbon particles show serious agglomeration and obvious increased particle size. This suggests a much enhanced stability of CNT HMS compared with traditional particles, which offers large opportunity for the practical applications in metal-air batteries or fuel cells.