Slow Diffusion Research Articles

Diffusion of oxygen in amorphous HfO2

We carefully prepared 100-nm-thick amorphous hafnia (a-HfO2) thin films of a homogeneous structure, and measured the diffusion profile of oxygen using secondary-ion mass spectrometry with a stable isotope (18O) as a tracer. The diffusion coefficient of oxygen, D, in a-HfO2 was 3.5 × 10−24 to 7.8 × 10−20 m2 s−1 at annealing temperatures from 300 to 500 °C, which are smaller than all previously reported values. The Arrhenius plots of D showed a curvature, from which we determined the activation energy for oxygen diffusion to be 1.42 and 2.24 eV for fast and slow diffusivity, respectively. Our results suggest the atomic movement of oxygen in a-HfO2 is very sensitive to the local structure.

Fast-diffusing receptor collisions with slow-diffusing peptide ligand assemble the ternary parathyroid hormone–GPCR–arrestin complex

The assembly of a peptide ligand, its receptor, and β-arrestin (βarr) into a ternary complex within the cell membrane is a crucial aspect of G protein-coupled receptor (GPCR) signaling. We explore this assembly by attaching fluorescent moieties to the parathyroid hormone (PTH) type 1 receptor (PTH1R), using PTH as a prototypical peptide hormone, along with βarr and clathrin, and recording dual-color single-molecule imaging at the plasma membrane of live cells. Here we show that PTH1R exhibits a near-Brownian diffusion, whereas unbound hormone displays limited mobility and slow lateral diffusion at the cell surface. The formation of the PTH–PTH1R–βarr complex occurs in three sequential steps: (1) receptor and ligand collisions, (2) phosphoinositide (PIP3)-dependent recruitment and conformational change of βarr molecules at the plasma membrane, and (3) collision of most βarr molecules with the ligand-bound receptor within clathrin clusters. Our results elucidate the non-random pathway by which PTH–PTH1R–βarr complex is formed and unveil the critical role of PIP3 in regulating GPCR signaling.

Li diffusion in plagioclase crystals and glasses – implications for timescales of geological processes

Abstract. The growing interest in Li diffusion as a tool to determine timescales of short-time magmatic events, such as magma ascent during eruption, increases the necessity to better understand Li diffusion in common mineral phases. In this context, well-constrained diffusion coefficients and understanding of kinetic processes specific to mineral phases are of crucial importance. To gain further insight especially into the kinetic processes in plagioclase, we investigated the diffusion of Li between natural An61 plagioclase crystals and synthetic glasses of An80 plagioclase composition. Experiments were conducted at 200 MPa in rapid-heat/rapid-quench cold-seal pressure vessels (RH/RQ CSPVs) and internally heated pressure vessels (IHPVs) at temperatures between 606 and 1114 °C. Concentration and isotope profiles of Li were measured using femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). We adopted a multispecies diffusion model and specified boundary conditions for plagioclase of labradoritic composition. Using this model, we were able to distinguish between an interstitial (DLii) and a vacancy process (DLiA), with the interstitial process being 0.2–1 orders of magnitude faster than the vacancy process, depending on temperature. DLii=10-3.76±0.58exp⁡-180.0±12.0kJmol-1RTm2s-1DLiA=10-5.53±0.16exp⁡-151.7±3.2kJmol-1RTm2s-1 Our data indicate charge compensation of Li by Na in both the crystal and the glass. Chemical Li diffusion coefficients in An80 glass are up to 3 orders of magnitude slower compared to Li tracer diffusion in silicate and aluminosilicate glasses and melts, which is attributed to slow Na diffusion at high An content. Our results for chemical diffusion of Li in plagioclase crystals are 1.5–2 orders of magnitude slower than Li tracer diffusion in An- and Ab-rich plagioclase determined in previous studies. This indicates that earlier studies on natural intermediate plagioclase compositions have underestimated timescales by up to 2 orders of magnitude. For accurate determination of timescales from Li diffusion in plagioclase we suggest further exploring the role of Na and a possible dependence on An content.

Experimental investigation on enhancing oil recovery of volcanic fractured oil reservoir by gas injection huff-n-puff considering gas diffusion

The pore structure of volcanic fractured oil reservoirs is complicated, and the traditional gas displacement and waterflooding are not ideal. In this paper, the pore structure characteristics of volcanic rock were analyzed. Then, the diffusion procedure of CO2 and natural gas in saturated oil porous media was analyzed by pressure drop method. Finally, huff-n-puff experiments of CO2 and natural gas were conducted to analyze factors on the recovery factor (RF), and the oil mobilization pattern was quantitatively characterized. By huff-n-puff, we mean injecting gas from one end and then soaking it for a period of time before producing oil, utilizing pressure-driven and physicochemical reactions to affect the oil. The results show that the pore size distribution range is large. The diffusion of CO2 and natural gas can be divided into three stages: rapid diffusion, slow diffusion and equilibrium, and the diffusion coefficient of CO2 is 10 times that of natural gas under same condition. Compared with vertical fractures and horizontal fractures, reticulate fractures have more influence on gas diffusion coefficient. After 6 cycles, the RF of CO2 is 15% higher than that of natural gas, and the contribution of the first 4 cycles to the RF is 91.38%. In addition, CO2 huff-n-puff primarily mobilizes oil in medium (0.1 μm < r < 1 μm) and large (r > 1 μm) pores. These research results can provide a good theoretical guidance for the efficient development of VFOR and CO2 sequestration.

Nanoconfinement-induced shift in photooxidative degradation pathway of polystyrene.

Polymer nanocomposites with high concentrations of nanoparticles (NPs) possess exceptional mechanical, transport, and thermal properties. To enable their widespread use in structural applications and functional coatings, it is crucial to understand how nanoconfinement and the polymer-NP interface influence polymer degradation under various environmental conditions, including prolonged UV exposure. In this study, we investigate the photooxidative degradation of polystyrene (PS)-confined in the interstices of SiO2 NP films. These nanocomposite films are prepared by the capillary rise infiltration (CaRI) of PS into interstices of SiO2 NP packings, and subsequently subjected to UV irradiation. Our investigation reveals that PS degradation progresses uniformly across the thickness, with degradation initiating from the center of the NP interstitial pores and extending towards the NP surface. We rationalize this degradation mechanism based on the disparity in the surface energies of PS and the NP surface, as well as slow oxygen diffusion through confined PS. We also demonstrate that packing smaller NPs at a given thickness or thicker packing of a specific NP size facilitates photooxidative degradation, highlighting the critical role of the number of interstitial pores in influencing degradation processes.

Holistic numerical simulation of a quenching process on a real-size multifilamentary superconducting coil

Superconductors play a crucial role in the advancement of high-field electromagnets. Unfortunately, their performance can be compromised by thermomagnetic instabilities, wherein the interplay of rapid magnetic and slow heat diffusion can result in catastrophic flux jumps, eventually leading to irreversible damage. This issue has long plagued high-Jc Nb3Sn wires at the core of high-field magnets. In this study, we introduce a large-scale GPU-optimized algorithm aimed at tackling the complex intertwined effects of electromagnetism, heating, and strain acting concomitantly during the quenching process of superconducting coils. We validate our model by conducting comparisons with magnetization measurements obtained from short multifilamentary Nb3Sn wires and further experimental tests conducted on solenoid coils while subject to ramping transport currents. Furthermore, leveraging our developed numerical algorithm, we unveil the dynamic propagation mechanisms underlying thermomagnetic instabilities (including flux jumps and quenches) within the coils. Remarkably, our findings reveal that the velocity field of flux jumps and quenches within the coil is correlated with the cumulated Joule heating over a time interval rather than solely being dependent on instantaneous Joule heating power or maximum temperature. These insights have the potential to optimize the design of next-generation superconducting magnets, thereby directly influencing a wide array of technologically relevant and multidisciplinary applications.

Prediction of cardiac remodeling and myocardial fibrosis in athletes based on IVIM-DWI images.

Myocardial microcirculation in athletes and its relationship with cardiac remodeling (CR) and myocardial fibrosis (MF) are not fully understood. We prospectively enrolled 174 athletes and 54 healthy sedentary controls for intravoxel incoherent motion (IVIM) diffusion-weighted imaging of cardiac magnetic resonance imaging. Athletes exhibited significantly lower fast apparent diffusion coefficient (ADCfast) and perfusion fraction (f)in 16 myocardial segments and each blood supply area compared to controls (p<0.05). Athletes with CR and/or MF had lower myocardial slow apparent diffusion coefficient (ADCslow) values than those without (p<0.05). A gradient boosting machine (GBM) effectively predicted CR and/or MF based on these hypoperfusion parameters, with an area under the receiver operating characteristic curve of 0.947 in the training set and 0.841 in the test set. The GBM model, leveraging IVIM parameters, could predict the occurrence of CR and/or MF, offering a potential tool for monitoring and managing the athletes' health.

Microstructural design opportunities and phase stability in the spray-formed AlCoCr0.75Cu0.5FeNi high entropy alloy

Designing a microstructure with controlled morphology is one of the determining factors for the optimum performance of a material. High entropy alloys (HEAs) have gained significant attention due to their enhanced mechanical and functional properties compared to conventional alloys, particularly based on opportunities for microstructural design. In this fast-developing field, varied thermal treatments can be applied to engineer a material as per the requirements. In the present work, we have studied the effect of thermal treatment on the microstructural modifications in the spray-formed AlCoCr0.75Cu0.5FeNi HEA. The alloy was characterized by using a light microscope, scanning electron microscope equipped with EDS detector and electron probe micro analyzer (EPMA). The elemental distribution and microstructural evolution of the alloy were studied by giving the heat treatments at different time-temperature spaces. The evolution of phases and their composition were correlated with the CALPHAD predicted property diagram and phase composition. It is observed that at a higher temperature of 1300°C, the alloy shows the simple solid solution phases to be more stable due to the high entropy effect, which brings down the Gibbs free energy of the system. The formation of the disordered BCC, FCC and their derivatives along with the sigma phase were observed in the temperature range of 600-1000°C. This work also draws attention to why understanding the microstructural evolution and solidification behaviour is important in designing the HEAs to meet the industrial promises and the role of entropy, enthalpy and slow diffusion kinetics are discussed.

Turbulent Transport Characteristics of the Particles within Pulsar Wind Nebulae 3C58 and G54.1+0.3

Turbulent transport characteristics of the particles within two Crab-like pulsar wind nebulae (PWNe), 3C58 and G54.1+0.3, are investigated in the framework of a time-dependent turbulent diffusion model. The model takes the gyroresonant interactions between the particles and turbulent waves into account, which enables us to self-consistently determine the energy and spatial coefficients of particles within the nebula via the distributions of turbulent waves. Our application of the model to the multiband emission from 3C58 and G54.1+0.3 reveals the following. (1) The energy and spatial diffusion coefficients seem to follow quasi-linear distributions in the Kolmogorov-type turbulence, but consistent with nonlinear distributions at low energies in the Kraichnan-type turbulence due to the effects of the turbulent scattering. (2) The stochastic acceleration and spatial diffusion processes may play a role in modifying the electron spectrum in the Kolmogorov-type turbulence, whereas in the Kraichnan-type turbulence the energy exchange between the turbulent waves and particles is more efficient, resulting in more significant effects of the stochastic acceleration and spatial diffusion processes on the electron spectrum at the low energies of E e ≲ 1 TeV. (3) At the high energies of E e ≳ 1 TeV, the diffusion transport appears to be less effective for the evolution of the particles within 3C58 and G54.1+0.3 because the synchrotron radiative cooling process dominates over the particle transport. These two Crab-like PWNe are expected to be electron PeVatrons in the Galaxy, with a common slow diffusion escape occurring in both 3C58 and G54.1+0.3.

A comparative study on Arc- and vacuum induction-melting for Ti16.6Zr16.6Hf16.6Co10Ni20Cu20 high entropy shape memory Alloy Production

Arc-melting (AM) as a primary method for casting high entropy alloys (HEAs) ensures rapid alloy screening with minimal material input, high cost-effectiveness, and high cooling rates. However, the limitations of AM on a laboratory scale, particularly its constrained sample size and the necessity for remelting steps to ensure homogeneity, hampers thorough mechanical and functional testing of bulk materials. Therefore, this study features a comparative analysis between AM and vacuum induction-melting (VIM) techniques for High Entropy Shape Memory Alloys (HE-SMAs) production, focusing on the senary alloy Ti16.6Zr16.6Hf16.6Co10Ni20Cu20, known for its potential functional applications and high sensitivity to material inhomogeneity. The alloy’s composition, including high-melting point elements like Hf, Ti and Zr, makes it a well-suited candidate for assessing the capabilities of VIM in producing homogeneous bulk materials. The employment of binary pre-alloys in both AM and VIM processes reduced the necessity for remelting steps and ensured better initial quality for subsequent heat treatments. A homogenization treatment at 900 °C for 100 h of an AM-produced senary alloy showed only slight improvements compared to the same alloy produced via VIM, largely due to the slow diffusion of the larger Hf and Zr atoms from the dendrites into the solid solution. This suggests that VIM can achieve comparable levels of homogenization in substantially less time than required for AM-treated samples. The findings finally indicate that by using VIM, when combined with binary pre-alloys, one achieves more homogeneous alloys with reduced heat-treatment time, making it a viable method for HE-SMA production.

Highly Efficient and Long-Lasting Chemiluminescence-Functionalized Nanohydrogel for Imaging-Guided Precise Piperlongumine Chemotherapy.

A major challenge for imaging-guided precise chemotherapy remains the ability to track the in situ real-time variation of the reactive oxygen species (ROS) level during treatment with prooxidation antitumor drugs. Chemiluminescence (CL) is widely used as an in vivo imaging tool with an excellent signal-to-noise ratio and high biological safety. However, suffering from flash-type and poor water solubility, most of the reported CL probes for ROS detection are unsuitable for in vivo long-term tracking. Herein, we designed a water-soluble CL nanohydrogel (L-012/Co2+@NGs) by cross-linking of vinyl-derived β-cyclodextrin monomer (MAH-β-CD) and loaded with luminol analog L-012 and cobalt ions (Co2+). In vitro studies reveal that L-012/Co2+@NGs exhibit long-lasting CL emission (up to 4 h) due to the slow diffusion of hydrogen peroxide in the nanohydrogel. High catalytic efficiency from the accelerated reduction of Co3+ to Co2+ through Tris and chelation of Co2+, as well as protection of the β-CD cavity against the active intermediate of L-012, enables L-012/Co2+@NGs to exhibit a 722-fold CL signal turn-on ratio and a nanomolar limit of detection (8.9 nmol/L). Piperlongumine (PL) was selected as a model of prooxidation drugs. The long-term and highly efficient CL strategy was designed for monitoring the local dynamic changes of ROS in PL-treated tumor-bearing mice for 150 min. The CL signal increased over time until reaching its maximum with a ∼6-fold increase at 15 min and then decreased slowly. The CL-functionalized nanohydrogel platform with good biocompatibility offers a great opportunity for imaging-guided precise tumor chemotherapy of PL and other prooxidation antitumor drugs.

The effects of maternal flow on placental diffusion-weighted MRI and intravoxel incoherent motion parameters.

To investigate and explain observed features of the placental DWI signal in healthy and compromised pregnancies using a mathematical model of maternal blood flow. Thirteen healthy and nine compromised third trimester pregnancies underwent pulse gradient spin echo DWI MRI, with the results compared to MRI data simulated from a 2D mathematical model of maternal blood flow through the placenta. Both sets of data were fitted to an intravoxel incoherent motion (IVIM) model, and a rebound model (defined within text), which described voxels that did not decay monotonically. Both the in vivo and simulated placentas were split into regions of interest (ROIs) to analyze how the signal varies and how IVIM and rebounding parameters change across the placental width. There was good agreement between the in vivo MRI data, and the data simulated from the mathematical model. Both sets of data included voxels showing a rebounding signal and voxels showing fast signal decay focused near the maternal side of the placenta. In vivo we found higher in the uterine wall and near the maternal side of the placenta, with the slow diffusion coefficient reduced in all ROIs in compromised pregnancy. A simulation based entirely on maternal blood explains key features observed in placental DWI, indicating the importance of maternal blood flow in interpreting placental MRI data, and providing potential new metrics for understanding changes in compromised placentas.

The nexus of overnight trend and asset prices in China

Leveraging the systematic variations in investor clientele within a day, we validate an adapted version of the Hong and Stein (1999) model that addresses the consequences of slow information diffusion in China. The model predicts that overnight returns, rather than total returns, strongly forecast future returns, as informed overnight clientele underreact to value-relevant signals. Empirically, we establish a consistent overnight trend phenomenon: Firms with a strong overnight trend reliably outperform those with a weak overnight trend in the subsequent month. The phenomenon is more pronounced among stocks with higher levels of information asymmetry, valuation uncertainty, and relative mispricing. Furthermore, the overnight trend predicts positively firm fundamentals in the cross section.

Explaining the Voltage Hysteresis and Slow Relaxation of Silicon Nanoparticles with a Chemo-Mechanical Particle-SEI Model

Silicon is widely considered to be a promising next-generation anode material, primarily due to its remarkably high theoretical capacity. Furthermore, silicon is an abundant, cheap, and widely spread material. However, a major challenge for the commercialization of silicon anodes is the significant voltage hysteresis reducing efficiency and leading to detrimental heat generation during fast-charging. Additionally, the hysteresis causes an unclear state-of-charge (SOC) to voltage relation impeding precise SOC estimation.The voltage hysteresis behavior of silicon anodes is addressed in literature with three different arguments: phase transformations, plastic flow of silicon, and slow diffusion. These approaches can interpret the voltage hysteresis of crystalline silicon, thin films, and large anode particles, respectively. Nevertheless, we show that they cannot explain the hysteresis observed for silicon anodes consisting of amorphous nanoparticles, the relevant material for next-generation lithium-ion batteries.Our investigation highlights the chemo-mechanical interplay between the silicon nanoparticle and the covering Solid-Electrolyte Interphase (SEI) as the underlying cause for the significant voltage hysteresis. The SEI, a thin passivating layer, forms on negative electrode particles due to electrolyte decomposition [1]. In the case of silicon particles, the volume changes during lithiation and delithiation result in massive strains and plastic deformation occurring within the SEI [2]. Our chemo-mechanical particle-SEI description successfully replicates the observed open-circuit voltage hysteresis in experiments and aligns with the Plett model [3]. Moreover, our visco-elastoplastic SEI model reproduces the voltage difference between slow cycling and the relaxed open-circuit voltage. In our recent work, we show that a sophisticated mechanical model explains the slow voltage relaxation observed for silicon nanoparticles as well as the observed C rate dependence [4].To conclude, we explain the voltage hysteresis and the slow voltage relaxation of silicon nanoparticles with a visco-elastoplastic particle-SEI model and discuss options to mitigate the size of the voltage hysteresis. This detailed physical understanding can improve the performance of all-silicon anodes and contribute to their commercialization.[1] Köbbing, L.; Latz, A.; Horstmann, B. J. Power Sources 2023, DOI: 10.1016/j.jpowsour.2023.232651.[2] Kolzenberg, L.; Latz, A.; Horstmann, B. Batter. Supercaps 2022, DOI: 10.1002/batt.202100216.[3] Köbbing, L.; Latz, A.; Horstmann, B. Adv. Funct. Mater. 2024, DOI: 10.1002/adfm.202308818.[4] Köbbing, L.; Latz, A.; Horstmann, B. (in preparation). Figure 1

(Invited) Local Environments on Cu Electrode Surface for Selective CO2 Electrolysis

Electrochemical CO2 reduction (eCO2R) attracts much attention as a technology for carbon circulation on the earth and the selective eCO2R for the production of high value-added chemicals is increasingly demanded. Hydroxide-derived copper (OH/Cu) electrodes exhibit excellent performance for eCO2R. However, the role of OH remains controversial and therefore the origin for the selectivity enhancement emerging on HO/Cu has not been fully understood. We the quantitatively evaluated surface OH by electroadsorption for the first time and established a direct correlation between the OH amount and selectivity for the production of CH4 and C2+ on OH/Cu with the help of computational investigations concerning work functions of the surface. Based on these findings, we demonstrated valuable selectivities using OH/Cu electrodes having a controlled OH amount; three OH/Cu electrodes realized their distinct selectivity such as Faradaic efficiency (FE) for the production of CH4 of 78%, FE of 71% for C2+, and the ratio of C2+-to-CH4 >355.[1] The proposed simple strategy for the selectivity control would contribute to further quantity synthesis of value added chemicals using eCO2R.The eCO2R in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO2 diffusion due to the absence of OH that facilitates the CO2 diffusion in an acidic environment. Here, we designed an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The eCO2R in acidic electrolytes exhibits a Faradaic efficiency of 87% for C2+ products.Direct air capture (DAC) and utilization of the captured CO2 (DAC-U) is a promising carbon neutral strategy to achieve an efficient carbon circulation on earth. DAC using membrane separation (m-DAC) is attracting much attention due to its lower energy consumption and its scalability. However, a higher energy input is still required to produce pure CO2. Given the preferred scalability of m-DAC, its combination with eCO2R may be suitable for on-site applications. Currently, high concentration and high purity CO2 gas is used in eCO2R studies, but, if low concentration and impure CO2 mixed gas becomes available, the cost of DAC-U using m-DAC can be significantly reduced. To date, only a few studies have evaluated eCO2R of CO2 feeds containing O2. Therefore, the development of systems that enable efficient eCO2R in the presence of O2, is critical to the establishment of DAC-U technology. Recently, we achieved eCO2R by direct introduction of 60% air containing CO2 using a porous Cu network formed on a hydrophobic gas diffusion layer. Even in the presence of 12% O2, Faradaic efficiency for the C2+ production reached 85% at a partial current density of 132 mA cm-2. Reference [1] M. Sun, A. Staykov, M. Yamauchi, ACS Catal.,12, 14856-14863 (2022). [2] M. Sun, J. Cheng, M. Yamauchi, Nat. Comm., 15, 491 (2024). [3] A. Anzai, M. Higashi, M. Yamauchi, Chem. Comm. , 59, 11188-11191 (2023).

Mechanism of Charge Transfer Via Dielectric Interfaces in Li Ion Battery

Lithium-ion batteries (LIBs) are utilized into the power source of the electric vehicles (EVs) due to their relatively high energy density (~200 Whkg-1), originating from high theoretical capacity of the bulk oxide electrodes. In order to deliver both excellent acceleration and better fuel efficiency, LIBs is required to achieve a good balance between high power density (low cell resistance) and high electric capacity. The high-rate capability of LIBs is generally limited by the slow charge transfer at the electrolyte–electrode interface. In particular, the slow Li diffusion through the solid electrolyte interfaces (SEIs), namely an undesirable byproduct, attributing to the electrolyte decomposition during cycling, severely increase the charge transfer resistance (R ct) of the cell. Oxide-layer decoration of the active material, e.g., Al2O3, can act as barrier layers to prevent undesirable side reactions at the electrolyte–active material interface, thus preventing the evolution of mentioned native SEIs [1]. Nanoscale coating of such protection layers, regarded as an artificial SEI, also allows a faster Li transfer at the electrolyte–cathode interface, rather than the Li diffusion via native SEIs, resulting in better high-rate characteristics. We have been proposing the partial surface decoration onto the active materials by dielectric nanoparticles as an artificial SEI, which enables faster charge transfer architecture via the surface Li diffusion of the dielectric layer [2]. For instance, incorporating BaTiO3 (BTO) nanoparticles into the surface of LiCoO2 (LCO) led to drastically enhanced high-rate capabilities. A series of experimental results and calculations utilizing density functional theory and molecular dynamics (DFT-MD) implied the improved activity at interfacial charge transfer is responsible for the faster Li adsorption and subsequent desolvation process at the dielectric surfaces. In this study, the dominant factors determining the adsorption and desolvation activities, which are strongly affecting high rate capability, were elucidated. The cell evaluations of the cathodes modified with various metal oxides SEIs, in addition to the conventional BTO based compounds, were performed as a function of the local chemical structure as well as the surface polarization between cation and neighborhood anions.[1] L. Daheron, R. Dedryvere, H. Martinez, D. Flahaut, M. Menetrier, C. Delmas, and D. Gonbeau, Chem. Mater, 21, (2009), 5607–5616.[2] T. Teranishi, K. Kozai, S. Yasuhara, S. Yasui, N. Ishida, K. Ishida, M. Nakayama, A. Kishimoto, Journal of Power Sources, 494, (2021) 229710.

Fast-Charging Li4Ti5O12 Anode Driven By Light

The development of fast-charging lithium-ion batteries (LIBs) is crucial for achieving significant market adoption of electric vehicles (EVs). The successful achievement of fast-charging LIBs depends on efficient charge transfer and the diffusivity of lithium ions. The photo-assisted battery system exhibits promising fast-charging properties. Previous research has shown that direct exposure to white light can induce a more oxidized center in a spinel LiMn2O4 (LMO) cathode, accelerating its charging rate.[ 1] Recently, our group found that illumination with red light on an operating LMO cathode induces an Mn d-d electron excitation, simultaneously shrinks the Mn-Mn lattice, and facilitates faster delithiation of the LMO cathode.[ 2] Consequently, the charging time of the battery decreases. This encourages us to consider whether the photon energy from a specific wavelength of light can also enhance the lithiation process on the anode side. Spinel Li4Ti5O12 (LTO) is a promising material for faster-charging anodes due to its small volume charge and high-rate capability in lithium intercalation. However, the system displays slow lithium diffusivity due to poor bulk ionic conductivity. To examine the photon effect of light on these anodes, we demonstrate the photo-accelerated fast-charging (lithiation process) mechanism with an LTO spinel anode.The thin film LTO's energy band gap (Eg), approximately 3.4 eV, was determined through intense UV-visible (UV-Vis) absorption spectrum analysis, assessed in a transmission mode employing Tauc’s Law. This indicates that an LED light with photon energy around 3.4 eV might trigger rapid charging by exciting electron transfer to the T-t2g band. To explore the impact of light on the fast-charging behavior of the LTO electrode, current was measured while applying a constant voltage of 1.2 V. During the 20-minute chronoamperometry experiment, utilizing the 3.4 eV UV LED to illuminate the cell resulted in a progressive increase in current. This current increase peaked at approximately 200s, leading to a maximum average capacity increase of 13 mA h g-1. This suggests that UV illumination accelerates the lithiation process compared to the dark state, particularly favoring the early lithiation stage. Subsequently, a red LED emitting 2 eV photon energy was used to illuminate the same cell, resulting in no discernible change in current levels compared to the dark state. Electrochemical impedance spectroscopy (EIS) further revealed a significant reduction in charge transfer resistance of the window cell when illuminated with UV light compared to both the dark state and red illumination. This alteration in electrode reaction kinetics at the interface suggests a distinct influence of different light wavelengths on the charging process.In addition to assessing charge transfer at the electrode interface, galvanostatic intermittent titration technique (GITT) analysis was conducted at a 2 C rate to further elucidate diffusion within the LTO electrode. The GITT curves reveal that the diffusion of Li+ ions was approximately 1.3 times faster when the cell was illuminated by UV light compared to dark conditions. Consequently, we deduce that photo-accelerated fast charging can also occur during the lithiation process (reduction reaction) of anode materials, driven by optical forces.To delve into the underlying mechanisms, we conducted first-principles density functional theory (DFT) calculations. The outcomes revealed that the generation of additional electrons in LTO results in a reduction in the bandgap and shifts the Fermi level above the conduction band minimum, effectively transforming LTO into an active conductor of electricity. These calculations indicate that UV light illumination has the capability to surmount the bandgap of LTO, generating electron-hole pairs and thereby facilitating charge transfer and lithium-ion diffusion.In conclusion, our study showcased that UV light illumination on the LTO anode can lead to a faster charging speed of approximately 17% compared to dark conditions. We posit that the observed phenomenon of photo-accelerated fast charging in LTO is linked to the formation of electron-hole pairs in intrinsically wide-bandgap insulators or semiconducting materials. This discovery holds considerable implications for the advancement of fast charging technologies for lithium-ion batteries, potentially mitigating range anxiety concerns and facilitating the widespread adoption of electric vehicles.Acknowledgments: This work was supported by funding from Royal Dutch Shell plc. Argonne National Laboratory operates under contract no. DE-AC02-06CH11357 with the U.S. Department of Energy Office of Science. We gratefully acknowledge use of the Bebop or Swing or Blues cluster in the Laboratory Computing Resource Center at Argonne National Laboratory and supported by the U.S. Department of Energy Office of Science.Reference[1] A. Lee et al., Nat. Commun., 10, 4946 (2019).[2] J. Lipton et al., Cell Reports Physical Science, 3, 101051 (2022).

(Invited) Improving Low-Temperature Lithium-Ion Battery Performance through 3D Structure-Controlled Anodes with Optimized Charge Storage Mechanisms

The performance of lithium (Li)-ion batteries (LIBs) significantly decreases at low temperatures, primarily due to the slow diffusion of Li ions within the graphite anode. This issue often necessitates the use of complex thermal control systems to safeguard the batteries, enhancing their cost, mass, and volume, especially under extreme conditions. Here, we introduce both structure-controlled graphene and graphite composite anodes, which employ controlled charge storage mechanisms to accelerate Li-ion charge storage kinetics and maintain structural stability under low-temperature conditions. [1-3] By transitioning from layered graphite to crumpled graphene or expanded graphite (composite), we effectively utilize diffusion- and surface-controlled charge storage mechanisms. These structure-controlled anodes exhibit superior rate capability and exceptional performance at temperatures as low as -50 °C. Through comprehensive low-temperature analyses, this research provides a detailed understanding of the relationships between anode structure, charge storage mechanisms, and performance under low-temperature conditions. Our findings offer valuable insights for the development of advanced energy storage devices optimized for low-temperature operation.

Finding the ideal solvent for the analysis of polar analytes using supercritical fluid chromatography.

The analysis of polar analytes with the help of hydrophilic interaction liquid chromatography (HILIC) using classic methods of high-performance liquid chromatography is not without its downsides. In these applications, acetonitrile is prevalent as main eluent and sample diluent. This results not only in slow diffusion processes during the separation, but also in often unstable sample solutions where polar analytes are concerned. Furthermore, there are ecological concerns. With the use of supercritical fluid chromatography (SFC) which uses supercritical carbon dioxide as eluent, and other green solvents as alternative for the sample preparation, the separation of polar analytes could be vastly improved with this technique. Fast diffusion within carbon dioxide led to shorter analysis times and higher plate numbers. Regarding sample diluents, small alcohols such as ethanol and 2-propanol, as well as acetone, yielded promising results while analytes showed higher solubility and stability within these solvents compared to acetonitrile. Other green solvents such as dihydrolevoglucosenone (Cyrene) and dimethyl carbonate were found to be unsuitable sample diluents for applications in SFC.

Highly selective recognition of l-tyrosine by perceiving huge luminescence turn-on of a cobalt (II) based metal-organic compound at physiological pH

Abnormal concentration of tyrosine in the human body is associated with many fatal diseases. Several medicinal supplements contain tyrosine, overuse of which can cause serious side effects. Therefore, accurate and selective detection and determination of tyrosine concentration is very crucial. Here we present a Co(II) based metal–organic compound (MOC) as a potential sensor for l-tyrosine that can be utilized in physiological pH. The MOC [Co(pzca)2(H2O)2], RT-1 has been synthesized by using Pyrazine-2-carboxylic acid (Hpzca) as organic ligand by employing a slow layer diffusion method at room temperature, which crystalizes in monoclinic crystal system with P21/c space group and is characterized by distorted octahedral geometry around the Co centre. The RT-1 upon excitation at 310 nm exhibited an emission band at 385 nm which showed a 42-fold turn-on along with a 20 nm red shift in the presence of l-tyrosine. It was found to be very selective to the l-tyrosine among the other amino acids and the limit of detection (LOD) was determined to be 0.68 µM or 123 ppb. Detailed investigations have also been conducted to establish that the luminescence behavior of RT-1 is not pH-sensitive in the physiological pH range. Hence the luminescence turn-on of the RT-1 in the presence of l-tyrosine is not attributed to alterations in the pH of the medium. The luminescence lifetime and quantum yield measurements revealed that due to the decrease in the non-radiative decay rates, the turn-on of the luminescence intensity occurred. The luminescence turn-on is the manifestation of the increased structural rigidity that has been achieved by the formation of an H-bonding network between one l-tyrosine and three units of RT-1.