Slow Diffusion Rate Research Articles

Ultrahigh rate and long-life nano-LiFePO4 cathode for Li-ion batteries

LiFePO4 is one of the most promising cathode materials for Li-ion batteries. However, its low electronic conductivity and slow Li-ion diffusion rate lead to poor electrochemical performance, especially poor rate performance. The hybrid of LiFePO4/Nitrogen and Sulfur co-doped graphene is successfully synthesized via a self-assembly method. Given its Nitrogen and Sulfur co-doped graphene matrix, the hybrid exerts a significantly impact on the electron conductivity of LiFePO4, resulting in excellent electrochemical properties and power density. The LiFePO4 composite has reversible capacity of 106.1 mAhg −1 at 10 C and 94.6 mAhg−1at 15 C. Moreover, with less than 5% loss of discharge capacity after 500 cycles at 10 C, the Nitrogen and Sulfur co-doped graphene can effectively improve the electrochemical performance of LiFePO4.

SnS/SnO heterostructures embedded in porous carbon microcages by boosting charge transfer for enhanced sodium-ion storage

ABSTRACTCurrently, tin based materials are widely explored as anode materials for sodium ion batteries due to their high theoretical capacity and large reserves. However, the practical applications of these materials are always hindered by their poor conductivity, slow sodium ion diffusion rate as well as complicated preparation process. Given this, a distinctive hybrid composite consisting of SnS/SnO heterostructures embedded inside multidimensional porous carbon microcages have been successfully synthesized through a facile one-pot method. Benefiting from the fascinating properties at SnS/SnO heterointerfaces, the optimized hybrid electrode yields a remarkable capacity of 274.7 mAh g−1 at 0.5 A g−1 and a good cycling stability with 70.1% capacity retention after 200 cycles. This method can provide inspiration in further innovation of other high-performance SIBs electrodes and create more possibilities for the implementation of large-scale production.

Stability of Zircon and Its Isotopic Ratios in High-Temperature Fluids: Long-Term (4 months) Isotope Exchange Experiment at 850°C and 50 MPa

Stability of zircon in hydrothermal fluids and vanishingly slow rates of diffusion identify zircon as a reliable recorder of its formation conditions in recent and ancient rocks. Debate, however, persists on how rapidly oxygen and key trace elements (e.g., Li, B, Pb) diffuse when zircon is exposed to hot aqueous fluids. Here, we report results of a nano- to micrometer-scale investigation of isotopic exchange using natural zircon from Mesa Falls Tuff (Yellowstone) treated with quartz-saturated, isotopically (18O, D, 7Li, and 11B) labeled water with a nominal δ18O value of +450‰ over 4 months at 850°C and 50 MPa. Frontside (crystal rim inwards) δ18O depth profiling of zircon by magnetic sector SIMS shows initially high but decreasing 18O/16O over a ~130 nm non-Fickian profile, with a decay length comparable to the signal from surficial Au coating deposited onto zircon. In contrast, backside (crystal interior outwards) depth profiling on a 2-3 µm thick wafer cut and thinned from treated zircon by focused ion beam (FIB) milling lacks any significant increase in 18O/16O during penetration of the original surface layer. Near-surface time-of-flight (TOF-SIMS) frontside profiles of uncoated zircon from 4-month and 1-day-long experiments as well as untreated zircons display similar enrichments of 18O over a distance of ~20 nm. All frontside 18O profiles are here interpreted as transient surface signals from nm-thick surface enrichment or contamination unrelated to diffusion. Likewise, frontside depth profiling of H, Li, and B isotopes are similar for long- and short-duration experiments. Additionally, surface U-Pb dating of zircon from the 4-month experiment returned U-Pb ages by depth profiling with ~1 µm penetration that were identical to untreated samples. Frontside and backside depth-profiling thus demonstrate that diffusive 18O enrichment in the presence of H2O is much slower than predicted from experiments in Watson and Cherniak (1997). Instead, intracrystalline exchange of oxygen between fluid and zircon in wet experimental conditions with excess silica occurred over length-scales equivalent to those predicted for dry diffusion. Oxygen diffusion coefficients even under wet conditions and elevated temperatures (850 °C) are <1-3×10-23 m2/sec, underscoring a virtual lack of oxygen diffusion and an outstanding survivability of zircons

Natural End Member Samples of Pyrope and Grossular: A Cathodoluminescence-Microscopy and -Spectra Case Study

Garnet is one of the most significant minerals in metamorphic rocks, that provides key information on prograde, peak-metamorphic and retrograde parts of the pressure-temperature (PT) path. Such results require a detailed knowledge of its different growth domains. For iron-poor compositions, the cathodoluminescence (CL) microscopy is an important and often overlooked method and allows to identify the internal structures of all garnet grains in one thin section within only a few seconds. The advantage of the CL-microscope is to deliver low magnification images in true color, not only of garnet but also, for instance, of other rock forming silicates, carbonates, sulfates, etc., of metamorphic, but also of sedimentary and magmatic origin, using polished thin sections. Internal structures of grossular from Mexico and pyrope from the Italian Alps were characterized and visualized by CL-microscopy. The different growth domains were additionally studied using CL-spectra and electron microprobe (EMP) analysis. Grossular shows a patchy zonation in its core while in mantle and rim zones oscillatory zoning is observed. It contains zones of anomalous birefringence, zones of orange and bluish luminescence and zones lacking luminescence. Different but low amounts of the activator elements Mn2+ and Eu2+ are responsible for the orange and bluish luminescent domains. Pyrope is also characterized by oscillatory growth zones, shows a dull luminescent core with a change of crystal morphology during growth, and displays an increase of brightness from core towards rim—the outermost rim, however, is lacking luminescence. The different luminescent zones are characterized by different amounts of Dy3+, Tb3+, Sm3+ and Sm2+ as activator elements. Because of slow diffusion rates of activators such as the REEs Sm, Dy and Tb, it can be still possible to visualize possible prograde and/or peak pressure stage growth domains of garnet, even if later high temperature events may have homogenized the major element profiles. Such domains may help to identify respective assemblages of mineral inclusions, and hence these results can represent an integral part of a detailed PT path. Thus the CL-information can be used as an important pathfinder prior to supplementary investigations, as for instance EMP, ion probe, mineral or fluid inclusion studies.

Tailoring the Kinetics of Sn Anodes for High Power Energy Storage Devices

Alkali ion batteries, such as Li-ion batteries (LIBs) and Na-ion batteries (NIBs), have recently drawn much attention due to their high energy densities, high Coulombic efficiencies and low self-discharge rates, making them useful in electronics, electric vehicles and grid-scale energy storage. One of the major obstacles to widespread applications of these rechargeable batteries, however, is their poor electrochemical performance under high power densities. The obstacle is attributed to the sluggish electrochemical kinetics, including slow diffusion rate of alkali ions in solid electrodes, low electrical conductivity and undesired phase transformation. Sn-based anodes having both high gravimetric and volumetric capacities are considered a promising candidate for next-generation LIBs and NIBs, but they also face the same challenge. Herein, we demonstrate that the electrochemical kinetics of Sn-based anodes, such as SnO2 and SnS2, can be largely enhanced by amorphization, doping of heteroatoms and facilitating the pseudocapacitive charge storage. The mechanistic insight of the enhanced kinetics is revealed by combining the electrochemical measurements with in situ TEM characterization and the first-principles calculations. Thanks to the new findings, we successfully fabricate Sb-doped SnO2/graphene-CNT aerogel anodes which deliver a high areal capacity of 2.6 mAh cm-2 at a high current density of 8 mA cm-2 in LIBs. The Na hybrid capacitor consisting of an activated carbon cathode and a SnS2/graphene-CNT aerogel anode is further developed for applications requiring high power densities and low costs. The as-assembled hybrid capacitor delivers an exceptional energy density of 26.9 Wh kg−1 at an ultrahigh power density of 6053 W kg−1. The implications of these discoveries for both fundamental understanding and practical applications are discussed.

Determination of diffusion coefficients of supercritical CO2 under tight oil reservoir conditions with pressure-decay method

A generalized methodology has been developed to determine the diffusion coefficients of supercritical CO2 under tight oil reservoir conditions considering the oil swelling effect. Experimentally, a diffusion cell has been used to perform diffusion tests for CO2 in tight formation cores, saturated with crude oil, under different pressure and temperature values. The dynamic pressure-decay curves of CO2 in the annular space of the diffusion cell were monitored and recorded during the measurements. Theoretically, the Peng–Robinson equation of state (PR EOS) with a modified α function has been incorporated to develop a one-dimensional radial diffusion model for the CO2–tight formation core systems. Also, the crude oil sample has been characterized as three pseudo-components for the accurate prediction of phase behavior of the CO2 and crude oil system. The CO2 diffusion coefficients, under different pressure and temperature values, were determined once the discrepancy between the measured and the calculated times, under the same pressure decrease of the diffusion process was minimized. According to the CO2 concentration profiles in the cores, the diffusion process is divided into two distinct parts, i.e., the early stage, characterized by the fast diffusion rate, and the later stage with the slow diffusion rate. While the pressure and the temperature increase, the CO2 diffusion coefficient initially increases quickly and then reaches a plateau. Lower viscosity of crude oil, higher temperature, and higher pressure facilitate the diffusion of CO2 into the crude oil, under tight formation conditions.

Dynamic Globularization Behavior of O-phase Lamellae in Ti-22Al-25Nb (at%) Alloy during Deformation at Elevated Temperatures

Abstract To clarify the globularization mechanism and model of the O-phase lamellae of Ti2AlNb-based alloys during deformation at elevated temperatures, the hot deformation behavior and microstructure evolution of Ti-22Al-25Nb (at%) alloy during hot compression deformation in (α2+O+B2) region were investigated. The results show that the flow softening is relevant to the dynamic globularization of O-phase lamellae and the flow instability including 45° shear deformation, 45° shear cracking and micro-cracks. The deformation constitutive model based on the exponential law was established and the deformation activation energy was calculated to be 831 kJ·mol−1. The globularization of O-phase lamellae is hard to occur at low temperatures or at high strain rates due to slow diffusion rate or insufficient diffusion time. The main globularization mechanism is the kink and shear of the O-phase lamellae, which is confirmed to be a dynamic recrystallization behavior. The dynamic globularization kinetics was also studied, which is sensitive to deformation conditions including deformation temperatures and strain rates and follows an Avrami type sigmoid equation.

High-Temperature Electrochemical Performance of FeF3/C Nanocomposite as a Cathode Material for Lithium-Ion Batteries

Iron trifluoride has been studied as a cathode material due to its cost-effectiveness, low toxicity, and high theoretical capacities of 712 mA h g−1. However, FeF3 has serious shortcomings of poor electronic conductivity and a slow diffusion rate of lithium ions, leading to a lower reversible specific capacity. In this work, FeF3/C nanocomposite has been synthesized successfully via a high-energy ball-milling method, and acetylene black is used as the conductive agent to improve the conductivity of FeF3. The FeF3/C nanocomposite shows a high initial discharge capacity of 346.25 and 161.58 mA h g−1 after 40th cycle at 50 mA g−1. It exhibits good cycle performance and rate performance. The high-temperature discharge capacities decreased with increase in the temperature. The initial high-temperature discharge capacities are found to be 254.17, 300.01, 281.25 and 125.16, and 216.875, 156, 141.67, 150, and 64.98 mA h g−1 at 20th cycles at the 40, 50, 60, and 70 °C, respectively.

Pharmacological Issues in Hearing Rehabilitation.

Surgery aimed at hearing rehabilitation risks damaging residual inner ear function, especially cochlear implant surgery. Pharmacological intervention to reduce this risk has shown great promise in animal models. The challenge is to deliver medication to the appropriate part of the inner ear in appropriate concentrations for long enough to be effective. Barriers to achieving these goals include: the blood/labyrinth barrier, limiting systemic drug delivery to the inner ear, slow rates of diffusion from the base of the cochlea to the apex, limiting intratympanic delivery from the middle ear to the cochlear apex, delayed intracochlear fibrosis, requiring extended medication delivery postoperatively. Intracochlear drug delivery via a drug-eluting cochlear implantation (CI) electrode may solve many of these pharmacologic issues. It is likely that more than one medication will be necessary to maximize inner ear protection and this may include steroids and appropriate growth factors. Such protection may also be helpful for otologic surgical procedures other than CI that have lower risks to hearing.

C-547, a 6-methyluracil derivative with long-lasting binding and rebinding on acetylcholinesterase: Pharmacokinetic and pharmacodynamic studies

C-547, a potent slow-binding inhibitor of acetylcholinesterase (AChE) was intravenously administered to rat (0.05 mg/kg). Pharmacokinetic profiles were determined in blood and different organs: extensor digitorum longus muscle, heart, liver, lungs and kidneys as a function of time. Pharmacokinetics (PK) was studied using non-compartmental and compartmental analyses. A 3-compartment model describes PK in blood. Most of injected C-547 binds to albumin in the bloodstream. The steady-state volume of distribution (3800 ml/kg) is 15 times larger than the distribution volume, indicating a good tissue distribution. C-547 is slowly eliminated (kel = 0.17 h−1; T1/2 = 4 h) from the bloodstream.Effect of C-547 on animal model of myasthenia gravis persists for more than 72 h, even though the drug is not analytically detectable in the blood. A PK/PD model was built to account for such a pharmacodynamical (PD) effect. Long-lasting effect results from micro-PD mechanisms: the slow-binding nature of inhibition, high affinity for AChE and long residence time on target at neuromuscular junction (NMJ). In addition, NMJ spatial constraints i.e. high concentration of AChE in a small volume, and slow diffusion rate of free C-547 out of NMJ, make possible effective rebinding of ligand. Thus, compared to other cholinesterase inhibitors used for palliative treatment of myasthenia gravis, C-547 is the most selective drug, displays a slow pharmacokinetics, and has the longest duration of action. This makes C-547 a promising drug leader for treatment of myasthenia gravis, and a template for development of other drugs against neurological diseases and for neuroprotection.

Two-Step Nanoscale Approach for Well-Defined Complex Alkanethiol Films on Au Surfaces.

Controlling the molecular organization of organic self-assembled monolayers (SAM) is of utmost importance in nanotechnology, molecular electronics, and surface science. Here we propose two well-differentiated approaches, double printing based on microcontact printing (μ-cp) and molecular backfilling adsorption, to produce complex alkanethiol films. The resulting films on model Au surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Double printing alkanethiols results in clear coexisting regions where no molecular displacement is observed, highlighting the slow diffusion rates of long alkanethiols and large attractive interaction between long alkyl chains. Exposing a single-print μ-cp Au substrate to an additional alkanethiol solution yields the formation of differently ordered domain boundaries with different thickness and micrometer lateral size. The high order is a result of enhanced molecular mobility and restructuring during solution backfilling. The formed molecular assemblies constitute an excellent testing ground for nanoscale phenomena that strongly depend on the nanoscale geometrical and chemical features of the surface such as designed functionality or corrosion initiation and inhibition.

Physical-chemical mechanisms of pattern formation during gastrulation.

Gastrulation is a fundamental phase during the biological development of most animals when a single layer of identical embryo cells is transformed into a three-layer structure, from which the organs start to develop. Despite a remarkable progress in quantifying the gastrulation processes, molecular mechanisms of these processes remain not well understood. Here we theoretically investigate early spatial patterning in a geometrically confined colony of embryonic stem cells. Using a reaction-diffusion model, a role of Bone-Morphogenetic Protein 4 (BMP4) signaling pathway in gastrulation is specifically analyzed. Our results show that for slow diffusion rates of BMP4 molecules, a new length scale appears, which is independent of the size of the system. This length scale separates the central region of the colony with uniform low concentrations of BMP molecules from the region near the colony edge where the concentration of signaling molecules is elevated. The roles of different components of the signaling pathway are also explained. Theoretical results are consistent with recent in vitro experiments, providing microscopic explanations for some features of early embryonic spatial patterning. Physical-chemical mechanisms of these processes are discussed.

Enhancement of mixing inside ionic liquid droplets through various micro-channels design

Ionic liquid (IL, [C4mim][BF4]) was introduced into micro-channels to form IL droplets and mixing performance inside the droplets was investigated via micro-LIF (laser induced fluorescence) technique. Experiments showed that mixing inside IL droplets generated in a simple cross-junction straight channel was very poor, due to the high viscosity and small diffusion coefficient of IL. To enhance the mixing inside IL droplets, two methods were then proposed. One was to change the way of droplet formation, which was achieved in T-junction and Y-inlet channels. The other was to change the way of droplet movement along the channel, which was achieved in meandering channel and deforming channel. Combing these two methods led to the design of Y-deforming channel, which resulted in excellent mixing inside IL droplets. Because of the extremely slow diffusion rate in IL, the circulation patterns and mixing characteristics within IL droplets were observed clearly in each type of micro-channels. Besides, mixing efficiency was defined and calculated, and its dependence on flow rates and droplet size were discussed in according channels. Based on the qualitative and quantitative analyses, mechanism of the mixing intensification brought by each micro-channel was clarified, and the core was to break the symmetrical circulation pattern inside IL droplets and introduce new vortices to enhance mixing.

The Neonatal Fc Receptor and Complement Fixation Facilitate Prophylactic Vaccine-Mediated Humoral Protection against Viral Infection in the Ocular Mucosa.

The capacity of licensed vaccines to protect the ocular surface against infection is limited. Common ocular pathogens, such as HSV-1, are increasingly recognized as major contributors to visual morbidity worldwide. Humoral immunity is an essential correlate of protection against HSV-1 pathogenesis and ocular pathology, yet the ability of Ab to protect against HSV-1 is deemed limited due to the slow IgG diffusion rate in the healthy cornea. We show that a live-attenuated HSV-1 vaccine elicits humoral immune responses that are unparalleled by a glycoprotein subunit vaccine vis-à-vis Ab persistence and host protection. The live-attenuated vaccine was used to assess the impact of the immunization route on vaccine efficacy. The hierarchical rankings of primary immunization route with respect to efficacy were s.c. ≥ mucosal > i.m. Prime-boost vaccination via sequential s.c. and i.m. administration yielded greater efficacy than any other primary immunization route alone. Moreover, our data support a role for complement in prophylactic protection, as evidenced by intracellular deposition of C3d in the corneal epithelium of vaccinated animals following challenge and delayed viral clearance in C3-deficient mice. We also identify that the neonatal Fc receptor (FcRn) is upregulated in the cornea following infection or injury concomitant with increased Ab perfusion. Lastly, selective small interfering RNA-mediated knockdown of FcRn in the cornea impeded protection against ocular HSV-1 challenge in vaccinated mice. Collectively, these findings establish a novel mechanism of humoral protection in the eye involving FcRn and may facilitate vaccine and therapeutic development for other ocular surface diseases.

Mechanisms of carbon dioxide acquisition and CO2 sensing in marine diatoms: a gateway to carbon metabolism.

Diatoms are one of the most successful marine eukaryotic algal groups, responsible for up to 20% of the annual global CO2 fixation. The evolution of a CO2-concentrating mechanism (CCM) allowed diatoms to overcome a number of serious constraints on photosynthesis in the marine environment, particularly low [CO2]aq in seawater relative to concentrations required by the CO2 fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), which is partly due to the slow diffusion rate of CO2 in water and a limited CO2 formation rate from [Formula: see text] in seawater. Diatoms use two alternative strategies to take up dissolved inorganic carbon (DIC) from the environment: one primarily relies on the direct uptake of [Formula: see text] through plasma-membrane type solute carrier (SLC) 4 family [Formula: see text] transporters and the other is more reliant on passive diffusion of CO2 formed by an external carbonic anhydrase (CA). Bicarbonate taken up into the cytoplasm is most likely then actively transported into the chloroplast stroma by SLC4-type transporters on the chloroplast membrane system. Bicarbonate in the stroma is converted into CO2 only in close proximity to RubisCO preventing unnecessary CO2 leakage. CAs play significant roles in mobilizing DIC as it is progressively moved towards the site of fixation. However, the evolutionary types and subcellular locations of CAs are not conserved between different diatoms, strongly suggesting that this DIC mobilization strategy likely evolved multiple times with different origins. By contrast, the recent discovery of the thylakoid luminal θ-CA indicates that the strategy to supply CO2 to RubisCO in the pyrenoid may be very similar to that of green algae, and strongly suggests convergent coevolution in CCM function of the thylakoid lumen not only among diatoms but among eukaryotic algae in general. In this review, both experimental and corresponding theoretical models of the diatom CCMs are discussed.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'.

Origin of the abnormal diffusion of transition metal atoms in rutile

Diffusion of dopants in rutile is the fundamental process that determines the performance of many devices in which rutile is used. The diffusion behavior is known to be highly sample-dependent, but the reasons for this are less well understood. Here, rutile is studied by using first-principles calculations, in order to unravel the microscopic origins of the diverse diffusion behaviors for different doping elements. Anomalous diffusion behavior in the open channel along [001] direction is found: larger atoms include Sc and Zr have lower energy barrier for diffusion via interstitial mechanism, apparently contradicting their known slow diffusion rate. To resolve this, we present an alternate model for the overall diffusion rate of the large-size dopants in rutile, showing that parallel to the [001] channel, it is limited by the formation of the interstitial states, whereas in the direction perpendicular to [001], it proceeds via a kick-out mechanism. By contrast, Co and Ni, prefer to stay in the interstitial site of rutile, and have conventional diffusion with a very small migration barrier in the [001] channel. This leads to highly anisotropic and fast diffusion. The diffusion mechanisms found in the present study can explain the diffusion data measured by experiments, and these findings provide novel understanding for the classic diffusion topic.

Carbon lock-in: an obstacle in higher education’s decarbonization pathways

Carbon lock-in describes a force that perpetuates the fossil fuel energy system despite known risks and cost-effective alternatives, a consequence of which is the slow rate of diffusion of low-carbon technologies. Hundreds of higher education institutions publicly commit to carbon neutrality goals, pledging to reduce energy consumption, to invest in renewable energy, and to offset unavoidable carbon emissions, but these conversations sometimes insufficiently address carbon lock-in effects and their associated future costs. To our knowledge, researchers have not applied the concept of carbon lock-in to higher education institutions and their climate commitments. We hypothesize that carbon lock-in effects will present a major obstacle to achieving carbon neutrality and expose these institutions to significant carbon liability, even with aggressive emissions mitigation efforts. Examples of fossil fuel-consuming infrastructure on our own campus and scenario analysis of emissions from eight higher education institutions in Ohio support this hypothesis. We find that carbon offset purchases to eliminate lock-in emissions could cost these institutions tens to hundreds of millions of dollars. Future regulatory penalties could impose similar costs, even on campuses without climate commitments. As a result, campus operations management should carefully consider further investment in carbon-emitting infrastructure, especially at institutions committing to carbon neutrality.

Intergranular diffusion rates from the analysis of garnet surfaces: Implications for metamorphic equilibration

ABSTRACTNovel approaches to garnet analysis have been used to assess rates of intergranular diffusion between different matrix phases and garnet porphyroblasts in a regionally metamorphosed staurolite‐mica‐schist from the Barrovian‐type area in Scotland. X‐ray maps and chemical traverses of planar porphyroblast surfaces reveal chemical heterogeneity of the garnet grain boundary linked to the nature of the adjacent matrix phase. The garnet preserves evidence of low temperature retrograde exchange with matrix minerals and diffusion profiles documenting cation movement along the garnet boundaries. Garnet–quartz and garnet–plagioclase boundaries preserve evidence of sluggish Mg, Mn and Fe diffusion at comparable rates to volume diffusion in garnet, whereas diffusion along garnet–biotite interfaces is much more effective. Evidence of particularly slow Al transport, probably coupled to Fe3+ exchange, is locally preserved on garnet surfaces adjacent to Fe‐oxide phases. The Ca distribution on the garnet surface shows the most complex behaviour, with long‐wavelength heterogeneities apparently unrelated to the matrix grain boundaries. This implies that the Ca content of garnet is controlled by local availability and is thought likely to reflect disequilibrium established during garnet growth. Geochemical anomalies on the garnet surfaces are also linked to the location of triple junctions between the porphyroblasts and the matrix phases, and imply enhanced transport along these channels. The slow rates of intergranular diffusion and the characteristics of different boundary types may explain many features associated with the prograde growth of garnet porphyroblasts. Thus, minerals such as quartz, Fe‐oxides and plagioclase whose boundaries with garnet are characterized by slow intergranular diffusion rates appear to be preferentially trapped as inclusions within porphyroblasts. As such grain boundary diffusion rates may be a significant kinetic impediment to metamorphic equilibrium and garnet may struggle to maintain chemical and textural equilibrium during growth in pelites.

Vertically Oriented Graphene Nanoribbon Fibers for High-Volumetric Energy Density All-Solid-State Asymmetric Supercapacitors.

Graphene fiber based micro-supercapacitors (GF micro-SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π-π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined-hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as-obtained fiber shows high length specific capacitance of 3.2 mF cm-1 and volumetric capacitance of 234.8 F cm-3 at 2 mV s-1 , as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all-solid-state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO2 coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm-3 and 5.7 mWh cm-3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro-SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.

A REE-in-plagioclase–clinopyroxene thermometer for crustal rocks

A REE-in-plagioclase-clinopyroxene thermometer has been developed on the basis of the temperature- and composition-dependent rare-earth element (REE) partitioning between coexisting plagioclase and clinopyroxene. This two-mineral exchange thermobarometer is constructed using parameters from lattice strain models for REE + Y partitioning in plagioclase and in clinopyroxene that were independently calibrated against experimentally determined mineral-melt partitioning data. An important advantage of this REE-based thermometer is that it can provide accurate temperatures through linear least-squares analysis of REE + Y as a group. Applications of the REE-in-plagioclase-clinopyroxene thermometer to volcanic and cumulate rocks show that temperatures derived from the new thermometer agree well with independently constrained magma crystallization temperatures, which adds confidence to applications of the REE-exchange thermometer to natural rocks with a wide spectrum of composition (i.e., from basalt to rhyolite). However, systematic temperature differences appear between the REE- and Mg-exchange thermometers for the volcanic and cumulate rocks. Through numerical simulations of diffusion in plagioclase-clinopyroxene systems, we demonstrate that (1) due to their slower diffusion rates, REE in minerals preferentially records crystallization or near-crystallization temperatures of the rock, and that (2) Mg is readily rest to lower temperatures for rocks from intermediately or slowly cooled magma bodies but records the initial crystallization temperatures of rocks from rapidly cooled magmas. Given their distinct diffusive responses to temperature changes, REE and Mg closure temperatures recorded by the two thermometers can be used in concert to study thermal and magmatic histories of plagioclase- and clinopyroxene-bearing rocks.