Binder Distribution Research Articles

Melt granulation: A comparison of granules produced via high-shear mixing and twin-screw granulation.

Melt granules of DI-CAFOS® A12 and 15% (w/w) Kolliphor® P407 were manufactured in a twin-screw granulator (TSG) at five different conditions (screw speed and throughput varied) and compared to granules manufactured in a high-shear granulator (HSG) (rotation speed of chopper/impeller and granulation time varied). Evaluated granules characteristics were process yield, particle-size distribution (PSD), particle morphology, flowability, porosity, specific surface area (SSA), tabletability, compressibility and binder distribution. Compared to TSG, granules produced from HSG were more spherical in shape with lower porosity, smaller mean particle size and a superior flowability. Granules made by TSG showed a more elongated structure, higher porosity and larger mean particle size with smaller SSA instead. Concerning the compression process of granules, tablets made of TSG granules exhibited a higher tabletability compared to HSG granules, whereas the compressibility remained similar. In the case of the TSG granules, energy-dispersive-X-ray (EDX) measurements of the tablet surface indicated an enhanced homogenous binder distribution. Additionally, the EDX-analyses determined that more binder was available between the individual particles, resulting in a stronger bonding.

Simple Approach: Heat Treatment to Improve the Electrochemical Performance of Commonly Used Anode Electrodes for Lithium-Ion Batteries.

The lithium-ion battery (LIB) industry has been in high demand for simple and effective methods to improve the electrochemical performance of LIBs. Here, we treated three different widely studied anode electrodes (i.e., Li4Ti5O12, TiO2, and graphite) under vacuum at 250 °C, and compared their electrochemical performance with and without a 250 °C treatment. Without changing the composition of the fabricated electrodes, all of the 250 °C treated electrodes exhibited enhanced specific capacities, and the lithium-ion diffusion was improved in different degrees. By comparing the results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy of the pristine and 250 °C treated electrodes, the 250 °C treatment improved the distribution of a polyvinylidene difluoride (PVDF) binder in the electrodes, resulting in a higher porosity of the 250 °C treated electrodes. The results of X-ray photoelectron spectrometry and SEM of the cycled electrodes confirmed that a uniform distribution of the PVDF binder from the 250 °C treatment played a positive role in the formation of a solid electrolyte interphase layer, thereby delivering higher capacities and capacity retentions than those of electrodes without heat treatment. The simplicity of this modification method provides considerable potential for building high-performance LIBs at a larger scale.

Effect of binder film distribution on the fatigue characteristics of asphalt Binder/Filler composite based on image analysis method

As a composition of asphalt binder and mineral fillers, asphalt mastic plays a significant role in the fatigue resistance of asphalt mixtures. At the mastic scale, the existence of fillers may rearrange the distribution of asphalt binder and then influence the fatigue characteristics of the binder/filler composite. The effect of content and size distribution of fillers on the binder film distribution in the asphalt mastic were evaluated by a series of image acquisition and processing methods, including scan electronic microscope (SEM), laser diffusion analyzer (LDA), randomly generation algorithm and morphology analysis. A normal distribution model could be used to fit the thickness distribution curve of the binder film within the asphalt mastic perfectly. The expected value (Ebinder) and peak value (Pbinder) were proposed to quantify the average level and uniformity of the binder film thickness, respectively. The rheological and fatigue properties of the asphalt mastic were evaluated by the time–temperature sweep (TTS) test and a modified linear amplitude sweep (LAS) test. Based on the correlation results, it could be found that asphalt mastic with higher filler contents and finer filler size distribution present a thinner and more uniform binder film distribution, which may increase the fatigue life at small strain level of 0.1% and the strain sensitivity under cyclic loading. The morphology analysis provides new insight to quantify the relationship between the microstructure characteristics and fatigue performance of asphalt mastic.

Study on Prediction of Binder Distribution in the Drying Process of the Coated Web of Positive Electrode for Lithium ion Battery

The slow and high energy consumption of drying process of the coated web of positive electrode for automotive lithium ion battery have become the bottleneck in the manufacturing process of cathode coating. However, high drying rate of solvent (commonly N-Methyl-2-pyrrolidone (NMP)) result in higher concentration of binder (commonly polyvinylidene fluoride (PVDF)) at the evaporating surface than at the bottom. The uneven distribution of binder between coating layers will lead to the decrease of adhesion between active layer and substrate, and even an increase in internal resistance and the associated deteriorated rate capability, thus seriously damaging the mechanical and electrochemical properties of the electrode. In order to improve the drying efficiency of the coated web, and regulate the concentration distribution of binder, this study mainly calculate the evaporation rate under different drying parameters. and determine the binder distribution at the different evaporation rates.

Fluorescence Microscopy for Determining Diffusion Coefficient Between Virgin and Aged Asphalt Binders

Diffusion between virgin and aged asphalt plays a critical role in ensuring a final uniform asphalt binder in mixtures containing recycled asphalt pavement (RAP). Understanding the diffusion phenomenon and determining the diffusion coefficient have a significant effect on asphalt mix design and asphalt mixture performance. In this study, a new method was proposed to utilize fluorescence microscopy to determine the diffusion coefficient of aged RAP binder in recycled mixtures. First, Fick’s second law was applied to quantify the diffusion process in a two-layered virgin-aged binder model and to obtain the analytical solution to the distribution of virgin and aged binders. Then, fluorescence microscopy was used in the laboratory to differentiate between virgin and aged binders and to back-calculate their concentrations from fluorescence image. The diffusion coefficient was determined by fitting the analytical solution to the laboratory concentration measurements. Comparison of the diffusion coefficient by the proposed method and that using the dynamic shear rheometer (DSR) method from the literature shows that the diffusion coefficient determined by fluorescence microscopy was of the same magnitude to, but slightly lower than, that by DSR method. The diffusion coefficient was also predicted using another theoretical method – free volume theory. Parameters describing the asphaltic model in the free volume theory were determined from analysis of the chemical structure of asphalt, viscoelastic relaxation properties, and glass transition temperature of asphalt as well as from the diffusion coefficient measured from laboratory experiments. Diffusion coefficient predicted by the free volume theory shows that diffusion coefficients of asphalt were closely dependent on temperature and asphalt type. A diffusion simulation was performed on plant mixtures using the diffusion coefficient obtained from fluorescence microscopy. The results showed that an almost complete diffusion was achieved within five minutes in a hot-mix asphalt mixture resulting in a uniform asphalt film.

The role of the screw profile on granular structure and mixing efficiency of a high-dose hydrophobic drug formulation during twin screw wet granulation.

This study aimed at systematically investigating the role of distributive comb mixing element (GLC) and neutral dispersive mixing kneading block element (K90) on the structure and physical properties of granules containing high-dose of poorly water-soluble drug. Albendazole was used as the model drug at 50wt% drug loading. Lactose monohydrate and microcrystalline cellulose were used as diluent, and 3 w/v% hydroxypropyl cellulose aqueous solution was used as binder liquid. It was found that the use of GLC element resulted in formation of granules with higher internal porosity, more homogeneous binder distribution, smaller particle size, superior compaction properties and tabletability while K90 kneading element produced relatively larger and denser granules with less homogeneous binder distribution where binder was mainly concentrated in larger granules. The use of downstream GLC element was shown to result in an approximately 8% and 57% reduction in the D50 for 0.2 and 0.3 liquid-to-solid ratios, demonstrating a significantly higher sensitivity of granule size to screw profile at higher liquid-to-solid ratios. The axial mixing efficiency was assessed by measuring the residence time distribution of the granulation process with screw profiles containing K90 and GLC elements. It was found that granules had longer mean residence time and broader residence time distribution within GLC element due to enhanced backmixing and axial dispersion processes. The continuous "fragmentation-reagglomeration" cycle was proposed to be the main advantage of distributive GLC element in granulation of hydrophobic powders.

Molecular weight distribution of asphalt binders from Laser Desorption Mass Spectroscopy (LDMS) technique and its relationship to linear viscoelastic relaxation spectra

Asphalt binder is a complex viscoelastic hydrocarbon, whose performance depends upon interaction between its physical and chemical properties, both of which are equally important to the successful understanding of the material. In this research effort, a physico-chemical relationship is developed by utilizing the technique of Laser Desorption Mass Spectroscopy (LDMS) to relate the molecular structure of asphalt binders to its viscoelastic properties. The molecular weight distribution (MWD) data obtained from the LDMS technique is used to develop a relationship between number average molecular weight and width of relaxation spectrum of asphalt binders obtained from linear viscoelastic characterization using dynamic shear rheometer. The relationship shows that as the molecular weight of asphalt binders increase, they require more time to relax the developed stresses. Also, the shape descriptors of the molecular weight distribution suggest that asphalt binders possessing greater asymmetry and kurtosis require more time to relax the developed stresses.

Direct Observation of Carboxymethyl Cellulose and Styrene-Butadiene Rubber Binder Distribution in Practical Graphite Anodes for Li-Ion Batteries.

Despite the important role of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) binders in graphite electrodes for Li-ion batteries, the direct analysis of these binders remains challenging, particularly at very low concentrations as in practical graphite anodes. In this paper, we report the systematic investigation of the physiochemical behavior of the CMC and SBR binders and direct observations of their distributions in practical graphite electrodes. The key to this unprecedented capability is combining the advantages of several analytic techniques, including laser-ablation laser-induced break-down spectroscopy, time of flight secondary ion mass spectrometry, and a surface and interfacial cutting analysis system. By correlating the vertical distribution with the adsorption behaviors of the CMC, our study reveals that the CMC migration toward the surface during the drying process depends on the degree of cross-linked binder-graphite network generation, which is determined by the surface property of graphite and CMC materials. The suggested analytical techniques enable the independent tracing of CMC and SBR, disclosing the different vertical distribution of SBR from that of the CMC binder in our practical graphite anodes. This achievement provides additional opportunity to analyze the correlation between the binder distribution and mechanical properties of the electrodes.

Composites with graphene as reinforcement

In this paper, the developments in the area of graphene-reinforced composite have been reviewed. It also depicts the work guided by the author. In the work, WC powder with 6% cobalt (Co) and graphene (0.2%) in the form of graphene nanoplatelets (GPLs) was prepared by high energy rate ball milling and ultrasonification. The mixture was sintered using spark plasma sintering at 1250ºC for 10 min. To study the effects of graphene reinforcement, the sample was analyzed for the physical (density), magnetic (coercivity, and magnetic saturation), microstructural (porosity) and mechanical properties (hardness, fracture toughness). Under Visual Inspection of the Spark Plasma Sintered (SPS) sample, the top surface showed more homogeneous distribution of the constituents than the bottom surface. The results of the surface measurements showed that the top and bottom surfaces have almost the same roughness. It was found that the SPS sample exceeded liquid phase sintered (LPS) specimens with respect to hardness and fracture toughness values. The coercive force was found to be higher for the LPS sample whereas the saturation magnetization value was found to be higher for the SPS sintered specimen. The density value is higher for the LPS sintered specimen. The presence of pores is seen in the back scattered electron (BSE) image. There was certain amount carbon pick up from the graphite die used in SPS. There was uniform distribution of the cobalt binder. The x-ray diffraction pattern for the SPS sintered sample indicates the presence of WC, Co and GNP.

Drying Process Research on High Energy Density LiNi1/3Co1/3Mn1/3O2 Electrode in Li-Ion Batteries

The most essential parameters in batteries are energy density, cost and safety. The cell energy density depends on the cell chemistry and geometry. In previous research, we made ultra-thick electrodes with optimum energy and power density for electric vehicles (EVs) and hybrid EVs (HEVs). Currently we developed a methodology such that the temperature of the laminates reached the temperature of the drying oven within a minute and drying of thick laminates at rates approaching industry (< 10 min). We examined the role of drying conditions of coated slurries on electrode morphology, binder distribution, binder crystallinity and in turn on the electrode’s mechanical and electrochemical properties. In our research, drying temperature has an impact on the components distribution in the electrode. The crystallinity of binder (poly vinylidene fluoride, PVDF) in the electrode is also dependent on drying temperature. From room temperature to 180 °C, the crystalline phase of PVDF membrane switched from β-phase to α-phase. The ionic conductivity is different in the two phases, which leads to different electrochemical performance of electrodes. Figure 1

A Study on the Influence of Ionization Method on Single Cell Initial Performance: Electrospray Method

Various catalysts showing high ORR activity have been developed over the past several years, and the results of evaluating actual fuel cells prepared using highly ORR-active catalysts have been reported. However, in contrast to rotating disk electrode (RDE) results showing high ORR activity, it is difficult to implement the high activity in actual fuel cell testinghen using the same catalysts. The most significant difference compared to the RDE is that there is an interface between the electrolyte and the surface of the catalyst in a membrane electrode assembly (MEA). In order to improve the coating properties of the electrolyte binder on the surface of the catalyst and the distribution of the electrolyte binder in the catalyst layer, various slurry[1] and catalyst layer preparation methods have been studied[2,3,4]. In this study, the catalyst layers were prepared using the electrospray (ES) method, and two different ionization methods (positive, negative) were used, based on surface charge analysis of the electrolyte binder (-35 mV) and electrolyte binder-coated catalysts (-43 mV). Structural differences in the catalyst layer were observed for the different ionization methods used. Mainly, it was observed that greater than 1 μm diameter pores were formed in the catalyst layer prepared by the positive ionization method. In contrast, with the negative ionization method, relatively uniform pores were formed in the catalyst layer. The initial performance of the MEAs prepared by the negative ionization method revealed improved initial performance over that of the positive ionization method: at 0.85 V, O2 supply, positive: 0.074, negative: 0.091 A/mgPt; at 0.65 V, air supply, positive: 1.26, negative: 2.10 A/mgPt; and O2 supply, positive: 3.86, negative 6.31 A/mgPt). The initial performance difference according to the ionization method can be understood through a structural difference in the catalyst layer analyzed by STEM and TEM, and through electrochemical analysis: i) different electrolyte binder morphology. ii) structural differences in the catalyst layer, and iii) proton transport resistance in the catalyst layer. Therefore, it was confirmed that, when the catalyst layer was prepared by the electrospray method using the same electrolyte binder content, the negative ionization method yielded around 1.5 times better initial performance, regardless of the single cell operating conditions. Acknowledgement This work was partially supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell (SPer-FC) Project" from the New Energy and Industrial Technology Development Organization (NEDO) and the "Yamanashi Frontier for Innovation and Ecosystem Project" from Regional Innovation Ecosystems of the Ministry of Education, Culture, Sports, Science and Technology.

(Invited) Process Development and Quality Control for Manufacturing of Lithium-Ion-Batteries

The development of efficient and sustainable low cost manufacturing techniques for the next generation lithium-ion cells with improved energy density is a key technology for industrial success. There is a strong need for further development of energy-efficient, resource and time saving electrode and cell manufacturing processes, which includes the identification of bottleneck factors along the whole production chain and the replacement of environmentally harmful intermediate steps (e.g. replacement of NMP for the cathode processing). One promising approach to increase both energy density of the cell and process efficiency is the reduction of passive materials in the cell by increasing the mass loading of active material on the electrodes. These thicker electrodes, however, suffer from some drawbacks like lower rate capability, lower mechanical flexibility and reduced adhesion to the current collector. In addition, the mixing and coating process parameters have to be adapted to avoid inhomogeneous binder distribution and mechanical disintegration of particles. The electrochemical and mechanical properties of the electrodes are strongly dependent on the 3D microstructure of the electrode (distribution of carbon black, porosity, distribution of the binder network). Both the mixing strategy during slurry preparation as well as the drying conditions during coating have a strong influence on the mechanical and electrochemical properties of the electrodes, which will be discussed in detail in the presentation. Another approach to optimize electrodes with high areal capacity is the preparation of 3D structured electrodes (e.g. gradient electrodes). We studied the addition of various pore forming additives and the preparation of multilayer electrodes via coating with a dual slot die system. On the anode side silicon based materials are quite attractive due to high specific capacity and energy. However, practical use of silicon is still limited to low amounts of silicon < 5wt% in commercial cells. Anodes with higher silicon content suffer from low cycling life due to high volume change and electrode swelling. A promising approach to improve the cycling life of silicon based electrodes is the use of alternative 3D structured current collectors in combination with adapted binder systems. In general, the cell manufacturing of Li-ion batteries requires precision and accuracy and includes a complex process chain with numerous process parameters. Optimized parameters for critical manufacturing steps during cell assembly as drying, slitting, electrolyte filling and formation will be presented and discussed in more detail.

Improvement of tabletability via twin-screw melt granulation: Focus on binder distribution.

In this study, the impact of binder distribution on the tabletability and compactibility of granules produced by twin-screw melt granulation was investigated. To this end, two grades of dicalcium phosphate anhydrous (fine and coarse) were used as model substances (filler) in combination with two grades of poloxamer (fine and coarse) as melt binder at three concentrations. For the fine filler, granule forming followed the immersion mechanism, whereas a distribution mechanism was observed in case of the coarse filler. Compared to the granules prepared with the coarse filler, the tabletability of granules prepared with the fine filler increased more pronouncedly compared to the corresponding physical mixtures (PM). In general, tabletability, compressibility and compactibility depended predominantly on the distribution of the binder in the tablet, and the homogeneity of distribution correlated with increased tensile strength. Binder distribution was analysed using scanning electron microscopy combined with energy-dispersive X-ray analysis (SEM/EDX) and quantified by image-analysis of the tablet surface. PMs in general varied in tabletability. However, even at tabletability similar to the granules, all PMs suffered from poor flow and/or segregation.

Evaluation of aggregate packing based on thickness distribution of asphalt binder, mastic and mortar within asphalt mixtures using multiscale methods

Aggregate packing is a key factor controlling the durability of asphalt mixtures. Considering the complex system of the aggregate structures, multiscale method was utilized by dividing asphalt mixtures into four scales, including asphalt binder, mastic, mortar and asphalt mixtures. Six asphalt mixtures with different gradation types and nominal maximum aggregate size (NMAS) were prepared and the corresponding mastics or mortars were also designed. Comprehensive image analysis methods, including high-resolution scanning, Scanning Electron Microscope (SEM), and Laser Diffraction Analyzer (LDA), were utilized to obtain the 2D images of asphalt mixtures, mortars and mastics. Then, the distribution curves of the binder within mastics, mastic within mortars, and mortar within asphalt mixtures were calculated and compared. New packing indexes were proposed, such as: expected value (Ebinder) and peak value (Pbinder) of the binder distribution at mastic scale, expected value (Emastic) and peak value (Pmastic) of the mastic distribution at mortar scale, expected value (Emortar) and peak value (Pmortar) of the mortar distribution at mixture scale. By comparing with volumetric parameters, it was found that Ebinder and Pbinder could correlate well with the volume ratio of filler to mastic. Emastic could correlate with the volume fraction of fine aggregate within the mortar, but the Pmastic may also influence by the fine aggregate gradation. The void filled with asphalt (VFA) has weak correlation with both packing indexes, Emortar and Pmortar, which indicates that VFA has limitation for evaluation of the packing properties of asphalt mixtures, and more indexes from the internal structure need to be considered.

Application of ATR-FTIR mapping to identification and distribution of pigments, binders and degradation products in a 17th century painting

Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and optical microscopy were applied to identify pigments, binders, fillers and degradation products in the 17th century painting 'The Coronation and Assumption of the Blessed Virgin Mary’. This piece of art is located in the Convent of the Sisters of St. Catherine in Orneta (Poland). The main important aspect is the non-destructive character of the examination and the small amount of sample necessary for analysis. Individual layers of five micro-samples cross-sections and powder samples taken from discrete and representative areas of the painting were studied. The combination of a linear array detector with a micro-ATR imaging accessory provides the possibility to overcome the diffraction limit and deliver a spatial resolution of about 5 microns (pixel size at the sample equal to 6.25 μm). Noteworthy, a rich palette of white, blue, red, and black pigments was characterized in the analyzed areas. Additionally, the mapping mode provided information about the distribution of individual components in the paint cross-sections. The analysis made it possible to identify binding media, such as proteins, triglycerides, fatty acids or resin acids, and degradation products, including whewellite, moolooite, and lead soaps.

In-Depth Analysis of Binder Distribution within Lithium-Ion Battery Electrode Using SAICAS

Microstructure and mechanical properties of lithium-ion battery (LIB) electrodes become more important as their loading levels increase highly for acheiving high energy density. In this point of view, we should control polymeric binder materials as well as nano-sized conductive materials within LIB electrodes. However, due to the limitation of appropriate analysis tools, it remains one of the challenging issues in LIBs. Fortunately, we have started using a new analysis tool, surface and interfacial cutting analysis system (SAICAS, Daipla Witnes, Japan), to measure adhesion properties of LIB composite electrodes as a function of depths. Based on the general principle, the adhesion strength is approximately propotional to the binder content, the polymeric binder distribution within the electrodes can be unveiled with a SAICAS. In this study, we prepared two LiCoO2 electrodes dried at totally different temperatures, 130 and 230oC, and used to confirm the feasibility to figure out the polymeric binder distribution in the electrode by using SAICAS. First, the adhesion strengths of those electrodes were deliberately measured at every 10 μm depth from the electrode surface as shown in Figure. Simultaneously, not only surface and cross-sectional SEM images but also corresponding EDS atomic mapping were checked to find correlation with adhesion strength. The electrochemical properties such as DC-IR, rate capability, and cycle life at room and high temperatures were also investigated.

Value-Added Application of Waste Rubber and Waste Plastic in Asphalt Binder as a Multifunctional Additive.

The feasibility and effectivity of recycling waste rubber and waste plastic (WRP) into asphalt binder as a waste treatment approach has been documented. However, directly blending WRP with asphalt binder brings secondary environmental pollution. Recent research has shown that the addition of WRP into asphalt binder may potentially improve the workability of asphalt binder without significantly compromising its mechanical properties. This study evaluates the feasibility of using the additives derived from WRP as a multifunctional additive which improves both the workability and mechanical properties of asphalt binder. For this purpose, WRP-derived additives were prepared in laboratory. Then, three empirical characteristics—viscosity, rutting factor, fatigue life were analyzed. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were employed to evaluate the effect of WRP-derived additive on the workability and chemical and mechanical properties of base binder. The dispersity of WRP-derived additive inside asphalt binder was also characterized using fluorescence microscope (FM). Results from this study showed that adding WRP-derived additive increases the workability of base binder. The WRP-derived additive appears positive on the high- and low- temperature performance as well as the fatigue life of base binder. The distribution of the WRP-derived additive inside base binder was uniform. In addition, the modification mechanism of WRP-derived additive was also proposed in this paper.

Study on the Distribution of Polymeric Binder in Lib Composite Electrodes By Measuring Adhesion at Different Depths

As the loading level or thickness of LIB composite electrodes increases, it becomes more difficult to uniformly distribute all components within the electrode. Because electric conductors are very small and light, they tend to rise upwards during drying process. Especially, to speed up the electrode fabrication process, not only drying temperature but also coating speed is maximized for reducing production costs. In this harsh condition, the polymeric binder tends to be unevenly distributed depending on the depth of electrode. Nevertheless, due to limited analysis tools, it had been left as research area to explore. Meanwhile, since a new tool, surface and interfacial cutting analysis system (SAICAS), was developed, the adhesion properties of the composite electrodes could be measured deliberately while changing the depth. Herein, we attempted to unveil the polymeric binder distribution by measuring the adhesion strength at different depths. In order to increase the reliability of the analytical results, composite electrode samples having different binder compositions and distributions were prepared and used for this study. At the same time, the compositional analysis with x-ray photoelectron spectroscopy were also conducted to confirm the binder distribution as a function of electrode depth. Finally, we investigated the effect of binder distribution on the electrochemical properties as well.

Nanofiber Fuel Cell MEAs with a PtCo/C Cathode

PtCo/C and Pt/C catalyst powders were incorporated into electrospun nanofiber and conventional sprayed cathode membrane-electrode-assemblies (MEAs) at a fixed electrode loading of 0.1 mgPt/cm2. The binder for PtCo/C nanofiber cathodes and Pt/C nanofiber anodes was a mixture of Nafion and poly(acrylic acid) (PAA), whereas the sprayed electrode MEAs utilized a neat Nafion binder. The structure of electrospun fibers was analyzed by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), which showed that the fibers were ∼30% porous with a uniform distribution of catalyst and binder in the axial and radial fiber directions. The initial performance of nanofiber MEAs at 80°C was 20% better than the sprayed electrode MEA (a maximum power density of 1,045 mW/cm2 vs. 869 mW/cm2). The benefit of the nanofiber electrode morphology was most evident at end-of-test (after a metal dissolution accelerated stress test), where power densities dropped by only 8%, after 30,000 square wave voltage cycles (0.6 V to 0.95 V), as compared to a 35% drop in the maximum power for the sprayed electrode MEA. The use of a recovery protocol improved the initial performance of a nanofiber MEA by ∼13%, to 1,070 mW/cm2 at 0.65 V, and increased the power after a metal dissolution stress test by 5–10% (e.g. 840 mW/cm2 at 0.65 V after 30,000 voltage cycles). At rated power, the nanofiber MEA generated more than 1,000 mW/cm2 at 99°C and a pressure of 250 kPaabs. The high performance and durability of PtCo/C nanofiber cathode MEAs is due to the combined effects of a highly active cathode catalyst and the unique nanofiber electrode morphology, where there is a uniform distribution of catalyst and binder (no agglomeration) and short transport pathways across the submicron diameter fibers (which lowers gas transfer resistance and facilitates water removal from the cathode).

Physico-chemo-rheological characterization of neat and polymer-modified asphalt binders

The physico-chemo-rheological properties of asphalt binder are critical for the long-term performance of asphalt pavement infrastructures. The objectives of this study are to characterize the physico-rheological properties of unmodified neat and polymer-modified asphalt binders with newly developed rheological performance tests, and further investigate the binder chemical properties as well as the possible performance relationship from macroscale to microscale perspective. Three neat asphalt binders and two styrene–butadiene–styrene (SBS) modified asphalt binders are selected in this study. The physical properties of asphalt binder include traditional penetration, softening point and ductility. The saturates, aromatics, resins and asphaltenes (SARA) fractionation test, gel permeation chromatography (GPC) and fourier transform infrared spectroscopy (FTIR) tests are respectively conducted to quantify the chemical composition, molecular weight distribution and structure properties of asphalt binders. The rheological rutting and fatigue resistance are evaluated through the multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and DSR-based elastic recovery (DSR-ER) tests. Experimental results indicate that the physical properties are only effective to distinguish the rheological performance of neat asphalt binders. The lower aromatics contents improve the binder rutting resistance and an unified relationship between aromatic contents and binder rutting performance is obtained for both neat and modified binders. In addition, increasing the amount of small asphalt molecules decrease the resistance to permanent deformation respectively for neat and modified binders. However, the small asphalt molecule is favorable for improving the binder fatigue performance. The large molecular size (LMS) parameter from GPC test is demonstrated a unified correlation to the fatigue life of both neat and modified binders.