Ion Depletion Research Articles

Potassium sulphate production from an aqueous sodium sulphate from lead‐acid battery recycling: Impact of feedstock impurities on products yields

AbstractThe increasing demand for renewable energy highlights the need for efficient energy storage solutions. Despite various available technologies, lead‐acid batteries remain preferred for many industrial applications due to their inherent advantages. However, their expanded use necessitates proper waste management and recycling practices. During lead‐acid battery recycling, Na₂SO₄ is generated as a waste product, which cannot be directly sold due to quality concerns and limited market demand. Consequently, advanced waste management techniques are required to comply with government regulations on industrial waste disposal. Despite these challenges, Na2SO4 serves as a vital precursor for producing K2SO4, a valuable fertilizer. Prior research on the glaserite process for converting Na2SO4 to K2SO4 has assumed Na2SO4 to be pure—without traces of impurities. However, Na2SO4 recovered from battery recycling contains various contaminants. To address this, HSC Chemistry software was used to model K2SO4 and NaCl production from impure Na2SO4 and KCl, considering feed impurities. Under ideal conditions—a 1 bar pressure, 25°C feed temperature, and 40°C reactor temperature—over 90% yield of K2SO4 and NaCl was achieved in the absence of impurities. However, the addition of impurities resulted in a reduction in yields. Notably, impurity levels ranging from 1% to 4% by weight still allowed for yields exceeding 90%. Furthermore, a review of reactor compositions revealed a significant depletion of potassium and chlorine ions which are crucial for K2SO4 and NaCl production as impurity levels varied from 0% to 10%. These findings emphasize the negative impact of impurities on K2SO4 and NaCl yields.

Rational design of ZnO-SnO2 Janus nanofibers for highly sensitive triethylamine detection

Herein, ZnO-SnO2 Janus nanofibers (NFs) were synthesized by a parallel electrospinning method and its sensing performances were tested. Considering the compositions of the two metal oxide semiconductors in Janus structure, different ratios of ZnO and SnO2 were designed and controlled. The optimum ratios of ZnO and SnO2 was 1:2 by analyzing their sensing performances to triethylamine (TEA) gas. Gas sensors based on ZS-12 Janus NFs exhibited a high response to TEA (45.2) and an excellent sensing response/recovery reproducibility. In order to investigate the sensing mechanism of Janus structure, ZnO NFs and SnO2 NFs were synthesized and used as controlled experiment. The results indicated that the heterostructures in Janus NFs is the key factor for the enhanced TEA sensing performances. The electrons flowed in the ZnO-SnO2 Janus structure leading to the variation of ionic oxygen species and electron depletion layer. These phenomena improved the reaction of TEA gas molecules with ionic oxygen species so that the TEA sensing performances were enhanced. Based on the Janus structures, a satisfactory gas sensor for detecting TEA gas were developed. Significantly, this work investigated the sensing mechanism of Janus structures and provided an efficient strategy for the gas sensing materials.

Atomic-scale probing of ion migration dynamics in Na3Ni2SbO6 cathode for sodium ion batteries

Honeycomb-layered phases like Na3Ni2SbO6 have been extensively researched as high-voltage and high-rate capability cathode materials for sodium-ion batteries. However, our understanding of the structural stability and dynamic reaction mechanisms of Na3Ni2SbO6 cathode during cycling, especially at atomic-scale, remains limited. Here, we track the microstructure evolution during extraction of Na+ ions in Na3Ni2SbO6 cathode at atomic scale in an aberration-corrected transmission electron microscope. The electron beam irradiation that can provide a driving force for the Na+ ion migration, allows us to mimic the battery charge process. By controlling the electron beam dose, we study the structure evolution behavior to obtain insights into understanding the work principle and failure mechanism of Na3Ni2SbO6 cathode under different charge rate conditions. We find that the real-time structural evolution and ion migration pathways of Na3Ni2SbO6 cathode are distinct under different electron beam doses. High-dose irradiation reveals Na ion depletion, surface cracks, and phase transformations, mimicking rapid capacity decay. In contrast, low-dose irradiation shows slower ion migration, ordered Na vacancy formation, and maintaining structural integrity, which more closely resembles the electrochemical process of actual battery. This study provides an atomistic understanding of the structural stability and Na ions deintercalation mechanism in Na3Ni2SbO6 cathodes, offering new insights into optimizing electrode materials.

Propensity of hydroxide and hydronium ions for the air-water and graphene-water interfaces from abinitio and force field simulations.

Understanding acids and bases at interfaces is relevant for a range of applications from environmental chemistry to energy storage. We present combined abinitio and force-field molecular dynamics simulations of hydrochloric acid and sodium hydroxide highly concentrated electrolytes at the interface with air and graphene. In agreement with surface tension measurements at the air-water interface, we find that HCl presents an ionic surface excess, while NaOH displays an ionic surface depletion, for both interfaces. We further show that graphene becomes less hydrophilic as the water ions concentration increases, with a transition to being hydrophobic for highly basic solutions. For HCl, we observe that hydronium adsorbs to both interfaces and orients strongly toward the water phase, due to the hydrogen bonding behavior of hydronium ions, which donate three hydrogen bonds to bulk water molecules when adsorbed at the interface. For NaOH, we observe density peaks of strongly oriented hydroxide ions at the interface with air and graphene. To extrapolate our results from concentrated electrolytes to dilute solutions, we perform single ion-pair abinitio simulations, as well as develop force-field parameters for ions and graphene that reproduce the density profiles at high concentrations. We find the behavior of hydronium ions to be rather independent of concentration. For NaOH electrolytes, the force-field simulations of dilute NaOH solutions suggest no hydroxide adsorption but some adsorption at high concentrations. For both interfaces, we predict that the surface potential is positive for HCl and close to neutral for NaOH.

Reimei Satellite Observations of Alfvénic Interaction Modulating Inverted‐V Electrons and Filamentary Auroral Forms at the Poleward Edge of a Discrete Arc

AbstractWe present an event based on Reimei satellite observations in the low‐altitude midnight auroral region, showing that intense and clear energy‐dispersed electron precipitations, repetitively generated by field‐aligned accelerations due to dispersive Alfvén waves, were modulating inverted‐V electrons. These Alfvénic electrons had peak energies equal to or slightly larger than those of the inverted‐Vs and were associated with the filamentary auroral forms rapidly streaming at the poleward edge of a broad discrete arc. This arc was caused by the inverted‐V accompanied by ion depletions produced by quasi‐electrostatic parallel potential drop. Assuming instantaneous electron accelerations over a wide energy range in a single location and a simple time‐of‐flight effect for the energy‐time dispersions, the Alfvénic source distances were estimated 1,500 ± 500 km above the satellite altitude of ∼676 km, a lower bound since the interaction locations are realistically distributed in altitudinally extended regions. The electron characteristics in detailed energy‐pitch angle distributions obtained at high time resolution can be categorized into: (a) original inverted‐V fluxes energized by quasi‐electrostatic upward electric field, (b) accelerated and decelerated/reduced inverted‐V fluxes, (c) field‐aligned energy‐dispersed precipitations accelerated by dispersive Alfvén waves, and (d) upwelling secondary components effectively produced by the field‐aligned precipitations particularly at energies of a few tens of eV. This event is useful to reveal the interactions between the inverted‐V and Alfvénic electrons and their related ionospheric effects in the magnetosphere‐ionosphere coupling processes. The detailed energy‐pitch angle distributions presented here provide constraints for models of these interactions and processes.

Selective Gas-Phase Depletion of Chemical Contaminants in Dissolved Organic Matter Increases Compositional Coverage by FT-ICR Mass Spectrometry.

Fourier transform ion cyclotron resonance mass spectrometry of dissolved organic matter (DOM) extracted from environmental samples provides molecular speciation that enables visualization of compositional trends in the fate and cycling of biogenic and anthropogenic organics. Often, chemical contamination is introduced during field sampling (i.e., remote locations, cannot use glass). Further, preconcentration of DOM by solid-phase extraction often results in chemical contamination. When chemical noise is a dominant fraction of the ion signal, mass spectral performance is degraded by reduction of the ion trap analyte accumulation capacity and enhanced ion cloud dephasing during ICR detection. We have developed gas-phase ion depletion of unwanted chemical contaminants during ion injection into the linear RF ion trap of the hybrid linear ion trap 21 T FT-ICR mass spectrometer that improves detection of analytes by removing unwanted chemical noise. We demonstrate improvements in signal-to-noise ratio, dynamic range, and the number of observed analytes in dissolved organic matter samples that results in a 40-100% increase in the number of identified analytes. In many cases, the number of peaks observed per nominal mass more than doubles over select m/z regions. This gas-phase "clean-up" can salvage precious samples challenged by sampling location, sample volume, or collection protocols that cannot be avoided and maximizes the compositional information obtained. Further, this approach is generalizable and extendable to any hybrid linear ion trap instrument platform (e.g., LTQ-Orbitrap or linear ion trap-TOF). We highlight the power of gas-phase depletion with electrospray ionization, but this method is also applicable to other ionization modes.

Acidic polymers reversibly deactivate phages due to pH changes.

Bacteriophages are promising as therapeutics and biotechnological tools, but they also present a problem for routine and commercial bacterial cultures, where contamination must be avoided. Poly(carboxylic acids) have been reported to inhibit phages' ability to infect their bacterial hosts and hence offer an exciting route to discover additives to prevent infection. Their mechanism and limitations have not been explored. Here, we report the role of pH in inactivating phages to determine if the polymers are unique or simply acidic. It is shown that lower pH (=3) triggered by either acidic polymers or similar changes in pH using HCl lead to inhibition. There is no inhibitory activity at higher pHs (in growth media). This was shown across a panel of phages and different molecular weights of commercial and controlled-radical polymerization-derived poly(acrylic acid)s. It is shown that poly(acrylic acid) leads to reversible deactivation of phage, but when the pH is adjusted using HCl alone the phage is irreversibly deactivated. Further experiments using metal binders ruled out ion depletion as the mode of action. These results show that polymeric phage inhibitors may work by unique mechanisms of action and that pH alone cannot explain the observed effects whilst also placing constraints on the practical utility of poly(acrylic acid).

Determination of nutrient concentration in liquid culture of cyanobacteria Nostoc sp. by capillary electrophoresis and inductively coupled plasma mass spectrometry

In this work, we demonstrate the use of capillary electrophoresis and inductively coupled plasma mass spectrometry, as competitive methods primarily for ion chromatography, to determine changes in the concentration of small inorganic ions in the Nostoc sp. culture medium. Although macronutrients were analyzed by capillary electrophoresis with conductivity detection, micronutrients were analyzed by inductively coupled plasma mass spectrometry. The different light settings (light intensity and spectral composition) had a visible effect on the culture growth and depletion of calcium, magnesium, and phosphate ions, and iron and manganese elements when comparing the behavior under red or violet light with that under blue light.

Investigation of Operational Parameters for Nanoelectrokinetic Purification and Preconcentration.

This work reports on experimental investigations into the operational parameters of nanoelectrokinetic purification and preconcentration, especially utilizing on ion concentration polarization (ICP). ICP as a nanoscale electrokinetic phenomenon has demonstrated promising advances in various fields utilizing an ion depletion zone (IDZ) with a steep electric field gradient inside the ICP layer. However, the inevitable electrokinetic instability occurring within the IDZ has posed a challenge in operating the ICP system stably. To address the need for a stable and efficient ICP operation in various devices and applications, we propose an operational strategy along with conducted research to determine optimal operating ranges. In order to investigate the operational parameters, a unit voltage (VTH) is introduced as the threshold for initiating ICP. We examined the applicability of VTH across various operating ranges to ensure its effectiveness and versatility. In ICP purification, we categorize three modes (steady, burst, and unsteady) based on IDZ expansion and stability under varying VTH and flow rate conditions, presenting optimal operational conditions that minimize the voltage margin. In ICP preconcentration, a systematic investigation is conducted to observe the influence of background electrolyte concentration and voltage conditions on preconcentration efficiency, offering insights into the correlation between preconcentration factor, electrical conditions, and preconcentration time. Therefore, this research would contribute to the practical understanding of nanoelectrokinetics, providing insight into experimental designs. These findings are expected to offer valuable guidance to researchers aiming to utilize ICP's potential across a spectrum of applications, from purification to preconcentration, in the realm of micro/nanofluidic systems.

Post-orogenic magmatic-hydrothermal system in the southern Songpan-Ganze Orogen, eastern Tibetan Plateau

ABSTRACT Post-orogenic magmatism is uncommon in the Songpan-Ganze Orogen (SGO), and could provide deep insights into geodynamic evolution and related metallogenesis. Here we present zircon U-Pb-Hf isotopes and whole-rock geochemical data, for post-orogenic granitoids newly identified in the southern SGO. The Longxigou and Yangfanggou granites yield crystallization age of ca. 165 Ma and εHf(t) values of +3.8 to −9.1. This age post-dates regional ca. 220–200 Ma orogenic magmatism and ca. 205–190 Ma peak metamorphism, and corresponds to ca. 200–150 Ma post-orogenic magmatism which is exemplified by neighbouring and coeval Wenjiaping and Wulaxi felsic plutons. They are crosscut by ca. 133 Ma granitic pegmatites, with εHf(t) values of −4.3 to −14.2. These post-orogenic granites show high SiO2 contents, as well as low Mg# values, (Zr + Nb + Ce + Y) concentrations and zircon saturation temperatures. They have continental crust-like REE patterns and trace element profiles, and exhibit negative Eu anomalies, enrichment in large ion lithophile elements and depletion in high field strength elements. Their mineral assemblages lack typical high-temperature (e.g. pyroxene and fayalite) and peraluminous (e.g. garnet and cordierite) varieties. All these features indicate an I-type granite affinity, and a dominant derivation from thickened lower crust. In comparison, these post-orogenic granites are compositionally distinct from regional late-orogenic (>200 Ma) categories, which have more positive εHf(t) values and higher Mg# values, with subduction-related signatures involving significant mantle components. Further, several high-grade stratiform Cu deposits and a tungsten deposit occur to the south of these granitic plutons, and have mineralization ages of 164–151 Ma together with biotite alteration age of ca. 134 Ma. Hence, ca. 165–133 Ma magmatic-hydrothermal system was most likely responsible for Cu-W mineralization and effective upgrading of metal deposits in the southern SGO.

Ultrathin Ionic Diodes with Electrostatically Heterogeneous Hybrid Interfaces of Nanoporous SiO2 Nanofilms and Polymer Layer-by-Layer Multilayers.

Nanofluidic ionic diodes have attracted much attention due to their unique functions as unidirectional ion transportation ability and promising applications from molecular sensing, and energy harvesting to emerging neuromorphic devices. However, it remains a challenge to fabricate diode-like nanofluidic systems with ultrathin film thickness <100nm. Herein the formation of ultrathin ionic diodes from hybrid nanoassemblies of nanoporous (NP) SiO2 nanofilms and polyelectrolyte layer-by-layer (LbL) multilayers is described. Ultrathin ionic diodes are prepared by integrating polyelectrolyte multilayers onto photo-oxidized NP SiO2 nanofilms obtained from silsesquioxane-containing block copolymer thin films as a template. The obtained ultrathin ionic diodes exhibit ion current rectification (ICR) properties with high ICR factor = ≈20 under low ionic strength and asymmetric pH conditions. It is concluded that this ICR behavior arises from effective ion accumulation and depletion at the interface of NP SiO2 nanofilms and LbL multilayers attributed to high ion selectivity by combining the experimental data and theoretical calculations using finite element methods. These results demonstrate that the hybrid nano assemblies of NP SiO2 nanofilms and polyelectrolyte LbL multilayers have potential applications for (bio)sensing materials and integrated ionic circuits for seamless connection of human-machine interfaces.

Remediation of soils contaminated with methomyl using electrochemically produced gaseous oxidants

This prospective work focuses on the use of two different gaseous oxidants (chlorine dioxide and ozone) to remediate soil polluted with methomyl in two different applications: ex-situ and in-situ. In the first, the soil washing is integrated with the bubbling of the oxidant, while in the second, the gas was introduced by a perforated pipe located sub-superficially. Regarding the soil washing treatment, results demonstrate that direct use of ozone is not very efficient, although an important improvement is obtained following activation with hydrogen peroxide or UV light. In contrast, chlorine dioxide exhibited complete methomyl depletion from the soil, although with higher energy consumption and technical complexity compared to ozone. The direct dosing of the gaseous oxidants in perforated pipes is effective, achieving methomyl removals of 7.8 % and 9.2 % using ozone and chlorine dioxide, respectively. In these cases, soil conditions are not significantly modified, which becomes an important advantage of the technology as compared with other electrochemically assisted soil remediation process, in which large regions of the treated soil are affected by important changes in the pH or by depletion of ions. This lower impact makes these novel technologies more promising for further evaluations.

Conductive layer coupled mesoporous hard carbon enabling high rate and initial Coulombic efficiency for potassium ion battery

Hard carbon with rich mesopores is considered as one of the most promising anodes for potassium-ion batteries, resulting from its shortened ions diffusion distance, good electrolyte penetration ability, and highly released stress. However, the well-developed pore channels tend to separate graphite-domains and enlarge direct contact area between electrode/electrolyte, which easily cause discontinuous electrons transfer paths and extra electrolyte depletion, thus leading to poor rate performance and initial Coulombic efficiency (ICE). Hence, we propose polyaniline conductive layer coated hollow mesoporous carbon spheres (HMCS@PAN) tailored based on local protonation reaction strategy, which can enhance conductivity and simultaneously maintain considerable pore structure, accounting for an ultrahigh-rate performance (233.9 mAh/g at 5 A/g) and long cycling life (216.8 mAh/g at 5 A/g over 2000 cycles). Besides, PAN coating can inhibit the direct contact between inner pore channels and electrolyte and reduce the excessive depletion of active ions in the filling of pores with larger pore size, which is conducive to building an even, stable, and inorganic-rich solid electrolyte interphase (SEI) layer, resulting in an excellent ICE (70.7%). This work provides a guidance for the structure design of mesopore hard carbon to improve its rate and ICE.

Electrophoretic deposition of TiO2 nanotubes and antibiotics on polyurethane coated stainless steel for improved antibacterial response and cell viability

In the quest for advancing the performance of metallic implants, surface modification emerges as a pivotal strategy to mitigate ion depletion, enhance the host's biological response, and exhibit anti-microbial behavior with reduced cytotoxicity. In this study, we developed a non-traditional electrophoretic deposition (EPD) hybrid coating for medical-grade stainless steel 316 L (SS316L) surfaces covered with a segmented polyurethane (SPU). These coatings are composed of anatase TiO2 nanotubes (TiO2_A), and antibiotics (nisin N or gentamicin G). We characterized the modified metals using FTIR and Raman spectroscopy, contact angle measurements, AFM, TGA, SEM-EDX, as well as assessing their antimicrobial response and cell cytotoxicity. The results demonstrate the formation of porous surfaces with embedded nanotubes and antibiotics within and on the polyurethane surfaces. Samples with SPU+ TiO2_AG EPD exhibited superior coverage, antimicrobial properties, and enhanced viability compared to cases where only particles or antibiotics were coated individually. Additionally, samples of SPU+ TiO2_AN EPD displayed favorable hydrophilicity and suitable cytotoxicity. Therefore, the synergistic effect of nanoparticles and antibiotics positively influences the functionality of the coating.

Dynamic Response of Ionic Current in Conical Nanopores.

Ionic current rectification (ICR) of charged conical nanopores has various applications in fields including nanofluidics, biosensing, and energy conversion, whose function is closely related to the dynamic response of nanopores. The occurrence of ICR originates from the ion enrichment and depletion in conical pores, whose formation is found to be affected by the scanning rate of voltages. Here, through time-dependent simulations, we investigate the variation of ion current under electric fields and the dynamic formation of ion enrichment and depletion, which can reflect the response time of conical nanopores. The response time of nanopores when ion enrichment forms, i.e., at the "on" state is significantly longer than that with the formation of ion depletion, i.e., at the "off" state. Our simulation results reveal the regulation of response time by different nanopore parameters including the surface charge density, pore length, tip, and base radius, as well as the applied conditions such as the voltage and bulk concentration. The response time of nanopores is closely related to the surface charge density, pore length, voltage, and bulk concentration. Our uncovered dynamic response mechanism of the ionic current can guide the design of nanofluidic devices with conical nanopores, including memristors, ionic switches, and rectifiers.

In-situ X-ray Fluorescence Analysis of In-plane Cerium-ion Distribution Under Humidity Gradients in Proton Exchange Membrane

Cerium ions are incorporated into proton exchange membranes (PEMs) of fuel cells to mitigate its chemical degradation caused by radical species. However, under fuel cell operating conditions, cerium ions move in in-plane direction in the cell by humidity gradient. This cerium ion transport results in cerium ion depletion leading to accelerated chemical degradation. This study developed an in-situ and operando measurement technique utilizing synchrotron high-energy X-ray fluorescence spectroscopy to monitor the cerium ion transport across the membrane under the in-plane humidity gradient. This method effectively tracks the dynamic behavior of cerium ions under fuel cell operating conditions.

Formation of deep arc root cumulates and implications for crustal growth in the southern Central Asian Orogenic Belt

Formation of ultramafic cumulate rocks at the arc root serves as a key process to understanding the deep evolution of arc magma and crustal growth. However, the arc root cumulates are easy to delaminate due to their high density, making limited field exposure. Here, we conducted comprehensive petrographic observations and geochemical analysis of typical ultramafic rocks (peridotites and pyroxenites) in an ophiolitic mélange from the central Beishan orogenic belt in the southern Central Asian Orogenic Belt (CAOB). Petrographic evidence shows that these rocks exhibit characteristic adcumulate and mesocumulate textures with intercumulus minerals such as olivine, orthopyroxene, and clinopyroxene. The mineral characteristics of ultramafic rocks, including olivine and orthopyroxene with lower NiO (0.10–0.33 wt% and 0.03–0.09 wt%, respectively) and Mg# (81–87 and 86–88, respectively), clinopyroxene with higher CaO (19.0–24.7 wt%), and spinel with lower Mg# (0–49), are distinct from those of mantle rocks but resemble cumulates. Both whole rock and calculated equilibrium melt exhibit the compositions of island arc magma characterized by enrichment in large ion lithophile elements (e.g., Cs, U, Pb, and Sr) and depletion in high field strength elements (e.g., Nb, Ta, Zr, Hf, and Ti). The covariation of high Mg# and low SiO2 in whole rocks is akin to typical arc root cumulates from classic island arcs (e.g., Kohistan and Talkeetna). The positive zircon εHf(t) values (+13 to +16) and calculated crystallization pressure of 0.9–1.1 GPa (∼30–40 km) support the formation of ultramafic cumulates in a juvenile island arc setting. These findings imply that most ultramafic rocks in the central Beishan orogenic belt are arc root cumulates instead of the mantle portion of an ophiolitic mélange. Fractional crystallization models suggest that arc root cumulate formation may have influenced the evolution of intermediate-felsic rocks in this area, and that the differentiation of hydrous arc magma played a crucial role in large-scale crustal growth in the southern CAOB during the early Paleozoic.

Differential Impact of Surface Conduction and Electroosmotic Flow on Ion Transport Enhancement by Microscale Auxiliary Structures.

Our research investigates the impact of auxiliary structures on ion transport in electrochemical systems such as batteries and microscale desalination units, whose importance for sustainable development has increased dramatically in recent decades. The electrochemical systems typically feature ion-selective surfaces, such as electrodes and ion exchange membranes, where ion depletion can cause performance issues including metal dendrite formation and flow instability. Recent research has shown that auxiliary structures in these electrochemical systems can enhance ion transfer near ion-selective surfaces, thereby resolving the instability problem and improving the energy conversion efficiency of the system. Our study leverages recent advancements in nanoscale electrokinetics to model these auxiliary structures as pillar arrays near an ion exchange membrane in a microchannel. We examine how these structures enhance ion transports relative to the characteristic length scale of microchannel depth and pillars' proximity to the ion-selective surface. Results show that the effect of the pillars varies significantly with their placement. Specifically, in deeper microchannels, where electrokinetic convection is stronger, the closer the auxiliary structure is to the ion-selective membrane, the better the ion transfer. However, in the thinner microchannel, the proximity of the auxiliary structure to the ion selective membrane has a less significant correlation with the ion transfer. Therefore, this finding highlights the importance of spatial arrangement of the auxiliary structures in improving the performance of electrochemical devices. Conclusively, this study can help to better understand energy conversion systems such as fuel cells, salinity gradient power generation systems, and electrochemical desalination systems, where auxiliary structures can be used in the vicinity of ion-selective surfaces. Especially, our fundamental electrokinetic study provides an effective means for designing the efficient electrochemical platforms utilizing micro/nanofluidics.

Ion Depletion Microenvironments Mapped at Active Electrochemical Interfaces with Operando Freezing Cryo-Electron Microscopy.

Interfacial structural and chemical evolution underpins safety, energy density, and lifetime in batteries and other electrochemical systems. During lithium electrodeposition, local nonequilibrium conditions can arise that promote heterogeneous lithium morphologies but are challenging to directly study, particularly at the nanoscale. Here we map chemical microenvironments at the active copper/electrolyte interface during lithium electrodeposition, presenting operando freezing cryogenic electron microscopy (cryo-EM), a new method, to lock in structures arising in coin cells. We find local ion depletion is correlated with lithium whiskers but not planar lithium, and we hypothesize that depletion stems from root-growing whiskers consuming ions at the growth interface while also restricting ion transport through local electrolyte. This can allow dangerous lithium morphologies to propagate, even in concentrated electrolytes, as ion depletion favors dendritic growth. Operando freezing cryo-EM thus reveals local microenvironments at active electrochemical interfaces to enable direct investigation of site-specific, nonequilibrium conditions that arise during operation of energy devices.

Spatiotemporal dynamic temperature variation dominated by ion behaviors during groundwater remediation using direct current

Direct current (DC) electric field has shown promising performance in contaminated site remediation, in which the Joule heating effect plays an important role but has been previously underappreciated. This study focuses on the spatiotemporal characteristics and mechanism of temperature change in heterogeneous porous media with applied DC. The heating process can be divided into four phases: preferential heating of the low permeability zone (LPZ), rapid heating in the middle region, temperature drop and hot zone shift, and reheating. The dynamic ion behaviors with complex interplays among reactions, electrokinetic-driven migration, and mixed convection induced an uneven redistribution of ions and dominated the heating rate and temperature distribution. The concentration of major ions near the pH jump decreased to 1% of the initial value, even though ions were continuously pumped into the heating zone. This ion depletion caused a drop in current, heating rate, and temperature. Here ions cannot be delivered rapidly into the ion-depleted zone by electromigration due to the potential flattening in the surrounding region. The presence of LPZ intensified the nonuniformity of ion redistribution, where a regional focusing of water-soluble ions was observed, and weakened the temperature rebound compared with that using homogeneous sand. These results provide a new perspective on the regulation of DC heating in site remediation.