Understanding the mechanisms of anisotropic dissolution in metal oxides by applying radiolysis simulations to liquid-phase TEM.

Iron-based redox-active minerals are ubiquitous in soils, sediments, and aquatic systems. Their dissolution is of great importance for microbial impacts on carbon cycling and the biogeochemistry of the lithosphere and hydrosphere. Despite its widespread significance and extensive prior study, the atomic-to-nanoscale mechanisms of dissolution remain poorly understood, particularly the interplay between acidic and reductive processes. Here, we use in situ liquid-phase-transmission electron microscopy (LP-TEM) and simulations of radiolysis to probe and control acidic versus reductive dissolution of akaganeite (ß-FeOOH) nanorods. Informed by crystal structure and surface chemistry, the balance between acidic dissolution at rod tips and reductive dissolution at rod sides was systematically varied using pH buffers, background chloride anions, and electron beam dose. We find that buffers, such as bis-tris, effectively inhibited dissolution by consuming radiolytic acidic and reducing species such as superoxides and aqueous electrons. In contrast, chloride anions simultaneously suppressed dissolution at rod tips by stabilizing structural elements while promoting dissolution at rod sides through surface complexation. Dissolution behaviors were systematically varied by shifting the balance between acidic and reductive attacks. The findings show LP-TEM combined with simulations of radiolysis effects can provide a unique and versatile platform for quantitatively investigating dissolution mechanisms, with implications for understanding metal cycling in natural environments and the development of tailored nanomaterials.

Multidimensional visualization of the dynamic evolution of Li metal via in situ/operando methods.

The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these "Li-free" cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick's law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. Our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies.

Emergence of tip singularities in dissolution patterns.

Chemical erosion, one of the two major erosion processes along with mechanical erosion, occurs when a soluble rock-like salt, gypsum, or limestone is dissolved in contact with a water flow. The coupling between the geometry of the rocks, the mass transfer, and the flow leads to the formation of remarkable patterns, like scallop patterns in caves. We emphasize the common presence of very sharp shapes and spikes, despite the diversity of hydrodynamic conditions and the nature of the soluble materials. We explain the generic emergence of such spikes in dissolution processes by a geometrical approach. Singularities at the interface emerge as a consequence of the erosion directed in the normal direction, when the surface displays curvature variations, like those associated with a dissolution pattern. First, we demonstrate the presence of singular structures in natural interfaces shaped by dissolution. Then, we propose simple surface evolution models of increasing complexity demonstrating the emergence of spikes and allowing us to explain at long term by coarsening the formation of cellular structures. Finally, we perform a dissolution pattern experiment driven by solutal convection, and we report the emergence of a cellular pattern following well the model predictions. Although the precise prediction of dissolution shapes necessitates performing a complete hydrodynamic study, we show that the characteristic spikes which are reported ultimately for dissolution shapes are explained generically by geometrical arguments due to the surface evolution. These findings can be applied to other ablation patterns, reported for example in melting ice.

Unveiling the structural transformation and activity origin of heteroatom-doped carbons for hydrogen evolution.

Heteroatom-doped carbon materials have been widely used in many electrocatalytic reduction reactions. Their structure-activity relationships are mainly explored based on the assumption that the doped carbon materials remain stable during electrocatalysis. However, the structural evolution of heteroatom-doped carbon materials is often ignored, and their active origins are still unclear. Herein, taking N-doped graphite flake (N-GP) as the research model, we present the hydrogenation of both N and C atoms and the consequent reconstruction of the carbon skeleton during the hydrogen evolution reaction (HER), accompanied by a remarkable promotion of the HER activity. The N dopants are gradually hydrogenated and almost completely dissolved in the form of ammonia. Theoretical simulations demonstrate that the hydrogenation of the N species leads to the reconstruction of the carbon skeleton from hexagonal to 5,7-topological rings (G5-7) with thermoneutral hydrogen adsorption and easy water dissociation. P-, S-, and Se-doped graphites also show similar removal of doped heteroatoms and the formation of G5-7 rings. Our work unveils the activity origin of heteroatom-doped carbon toward the HER and opens a door to rethinking the structure-performance relationships of carbon-based materials for other electrocatalytic reduction reactions.

Dissolution-driven propulsion of floating solids.

We show that unconstrained asymmetric dissolving solids floating in a fluid can move rectilinearly as a result of attached density currents which occur along their inclined surfaces. Solids in the form of boats composed of centimeter-scale sugar and salt slabs attached to a buoy are observed to move rapidly in water with speeds up to 5 mm/s determined by the inclination angle and orientation of the dissolving surfaces. While symmetric boats drift slowly, asymmetric boats are observed to accelerate rapidly along a line before reaching a terminal velocity when their drag matches the thrust generated by dissolution. By visualizing the flow around the body, we show that the boat velocity is always directed opposite to the horizontal component of the density current. We derive the thrust acting on the body from its measured kinematics and show that the propulsion mechanism is consistent with the unbalanced momentum generated by the attached density current. We obtain an analytical formula for the body speed depending on geometry and material properties and show that it captures the observed trends reasonably. Our analysis shows that the gravity current sets the scale of the body speed consistent with our observations, and we estimate that speeds can grow slowly as the cube root of the length of the inclined dissolving surface. The dynamics of dissolving solids demonstrated here applies equally well to solids undergoing phase change and may enhance the drift of melting icebergs, besides unraveling a primal strategy by which to achieve locomotion in active matter.

Probing multiscale dissolution dynamics in natural rocks through microfluidics and compositional analysis.

Mineral dissolution significantly impacts many geological systems. Carbon released by diagenesis, carbon sequestration, and acid injection are examples where geochemical reactions, fluid flow, and solute transport are strongly coupled. The complexity in these systems involves interplay between various mechanisms that operate at timescales ranging from microseconds to years. Current experimental techniques characterize dissolution processes using static images that are acquired with long measurement times and/or low spatial resolution. These limitations prevent direct observation of how dissolution reactions progress within an intact rock with spatially heterogeneous mineralogy and morphology. We utilize microfluidic cells embedded with thin rock samples to visualize dissolution with significant temporal resolution (100 ms) in a large observation window (3 × 3 mm). We injected acidic fluid into eight shale samples ranging from 8 to 86 wt % carbonate. The pre- and postreaction microstructures are characterized at the scale of pores (0.1 to 1 µm) and fractures (1 to 1,000 µm). We observe that nonreactive particle exposure, fracture morphology, and loss of rock strength are strongly dependent on both the relative volume of reactive grains and their distribution. Time-resolved images of the rock unveil the spatiotemporal dynamics of dissolution, including two-phase flow effects in real time and illustrate the changes in the fracture interface across the range of compositions. Moreover, the dynamical data provide an approach for characterizing reactivity parameters of natural heterogeneous samples when porous media effects are not negligible. The platform and workflow provide real-time characterization of geochemical reactions and inform various subsurface engineering processes.

Separations of romantic relationships are experienced differently by initiators and noninitiators.

Divorces are predominantly initiated by one spouse alone. This might suggest that one spouse typically benefits from divorce (the initiator), while the other is disadvantaged (the noninitiator). At the same time, empirical research on the consequences of divorce commonly focuses on the average effect for both partners. In contrast, I estimate separation trajectories individually for initiators and noninitiators of formerly cohabitating or married couples. The analysis covers a wide range of outcomes and a long period of time surrounding the separation. I employ an event-study design based on individual fixed effects, thereby accounting for time-invariant individual heterogeneity that could be linked to initiator status and the outcomes. The results reveal substantial differences in separation trajectories between initiators and noninitiators. Initiators indeed improve their subjective well-being after a separation and also see gains in other life domains, with the exception of the economic domain. Noninitiators experience significant short-term losses in subjective well-being, from which they recover in the long run. Noninitiators' trajectories in other life domains vary.

High-Speed Three-Dimensional Scanning Force Microscopy Visualization of Subnanoscale Hydration Structures on Dissolving Calcite Step Edges.

Hydration at solid-liquid interfaces plays an essential role in a wide range of phenomena in biology and in materials and Earth sciences. However, the atomic-scale dynamics of hydration have remained elusive because of difficulties associated with their direct visualization. In this work, a high-speed three-dimensional (3D) scanning force microscopy technique that produces 3D images of solid-liquid interfaces with subnanoscale resolution at a rate of 1.6 s per 3D image was developed. Using this technique, direct 3D images of moving step edges were acquired during calcite dissolution in water, and hydration structures on transition regions were visualized. A Ca(OH)2 monolayer was found to form along the step edge as an intermediate state during dissolution. This imaging process also showed that hydration layers extended from the upper terraces to the transition regions to stabilize adsorbed Ca(OH)2. This technique provides information that cannot be obtained via conventional 1D/2D measurement methods.

Chemomechanical Origins of the Dynamic Evolution of Isolated Li Filaments in Inorganic Solid-State Electrolytes.

The penetrating growth of Li into the inorganic solid-state electrolyte (SSE) is one key factor limiting its practical application. Research to understand the underlying mechanism of Li penetration has been ongoing for years and is continuing. Here, we report an in situ scanning electron microscopy methodology to investigate the dynamic behaviors of isolated Li filaments in the garnet SSE under practical cycling conditions. We find that the filaments tend to grow in the SSE, while surprisingly, those filaments can self-dissolve with a decrease in the current density without a reversal of the current direction. We further build a coupled electro-chemo-mechanical model to assess the interplay between electrochemistry and mechanics during the dynamic evolution of filaments. We reveal that filament growth is strongly regulated by the competition between the electrochemical driving force and mechanical resistive force. The numerical results provide rational guidance for the design of solid-state batteries with excellent properties.

Mechanisms of intestinal pharmacokinetic natural product-drug interactions.

The growing co-consumption of botanical natural products with conventional medications has intensified the need to understand potential effects on drug safety and efficacy. This review delves into the intricacies of intestinal pharmacokinetic interactions between botanical natural products and drugs, such as alterations in drug solubility, permeability, transporter activity, and enzyme-mediated metabolism. It emphasizes the importance of understanding how drug solubility, dissolution, and osmolality interplay with botanical constituents in the gastrointestinal tract, potentially altering drug absorption and systemic exposure. Unlike reviews that focus primarily on enzyme and transporter mechanisms, this article highlights the lesser known but equally important mechanisms of interaction. Applying the Biopharmaceutics Drug Disposition Classification System (BDDCS) can serve as a framework for predicting and understanding these interactions. Through a comprehensive examination of specific botanical natural products such as byakkokaninjinto, green tea catechins, goldenseal, spinach extract, and quercetin, we illustrate the diversity of these interactions and their dependence on the physicochemical properties of the drug and the botanical constituents involved. This understanding is vital for healthcare professionals to effectively anticipate and manage potential natural product-drug interactions, ensuring optimal patient therapeutic outcomes. By exploring these emerging mechanisms, we aim to broaden the scope of natural product-drug interaction research and encourage comprehensive studies to better elucidate complex mechanisms.

Assessing and mitigating pH-mediated DDI risks in drug development - formulation approaches and clinical considerations.

pH-mediated drug-drug interactions (DDI) is a prevalent DDI in drug development, especially for weak base compounds with highly pH-dependent solubility. FDA has released a guidance on the evaluation of pH-mediated DDI assessments using in vitro testing and clinical studies. Currently, there is no common practice of ways of testing across the academia and industry. The development of biopredictive method and physiologically-based biopharmaceutics modeling (PBBM) approaches to assess acid-reducing agent (ARA)-DDI have been proven with accurate prediction and could decrease drug development burden, inform clinical design and potentially waive clinical studies. Formulation strategies and careful clinical design could help mitigate the pH-mediated DDI to avoid more clinical studies and label restrictions, ultimately benefiting the patient. In this review paper, a detailed introduction on biorelevant dissolution testing, preclinical and clinical study requirement and PBPK modeling approaches to assess ARA-DDI are described. An improved decision tree for pH-mediated DDI is proposed. Potential mitigations including clinical or formulation strategies are discussed.

Visualization of Multiphase Reactive Flow and Mass Transfer in Functionalized Microfluidic Porous Media.

Multiphase reactive flow in porous media is an important research topic in many natural and industrial processes. In the present work, photolithography is adopted to fabricate multicomponent mineral porous media in a microchannel, microfluidics experiments are conducted to capture the multiphase reactive flow, methyl violet 2B is employed to visualize the real-time concentration field of the acid solution and a sophisticated image processing method is developed to obtain the quantitative results of the distribution of different phases. With the advanced methods, experiments are conducted with different acid concentration and inlet velocity in different porous structures with different phenomena captured. Under a low acid concentration, the reaction will be single phase. In the gaseous cases with higher acid concentration, preferential flow paths with faster flow and reaction are formed by the multiphase hydrodynamic instabilities. In the experiments with different inlet velocities, it is observed that a higher inlet velocity will lead to a faster reaction but less gas bubbles generated. In contrast, more gas bubbles would be generated and block the flow and reaction under a lower inlet velocity. Finally, in heterogeneous structures, fractures or cavities would significantly redirect the flow and promote the formation of preferential flow path nearby.

Robustly Boosting Thermoelectric Performance of N-Type PbSe via Lattice Plainification and Dynamic Doping.

Ideal thermoelectrics shall possess a high average ZT, which relies on high carrier mobility and appropriate carrier density at operating temperature. However, conventional doping usually results in a temperature-independent carrier concentration, making performance optimization over a wide temperature range be challenging. This work demonstrates the combination of lattice plainification and dynamic doping strategies is an effective route to boost the average ZT of N-type PbSe. Because Sn and Pb have similar ionic radii and electronegativity, this allows Sn to fill the intrinsic Pb vacancies and effectively improves the carrier mobility of PbSe to 1300 cm2 V-1 s-1. Furthermore, a trace amount of Cu is introduced into the Sn-filled PbSe to optimize the carrier concentration. The extra Cu is situated in the interstitial sides of the lattice, which undergoes a dissolution-precipitation process with temperature, leading to a strongly temperature-dependent carrier density in the material. This dynamic doping effectively improves the electrical transport properties and is also valid to suppress the lattice thermal conductivity. Ultimately, the resulting PbSn0.004Se+3‰Cu obtains a maximum ZT of ≈1.7 at 800 K and an average ZT of ≈1.0, with a 7.7% power generation efficiency in a single-arm device, showing significant potential for commercial application.

Launching a Drop via Interplay of Buoyancy and Stick-Jump Dissolution.

According to Archimedes' principle, a submerged object with a density lower than that of aqueous acid solution is more buoyant than a smaller one. In this work, a remarkable phenomenon is reported wherein a dissolving drop on a substrate rises in the water only after it has diminished to a much smaller size, though the buoyancy is smaller. The drop consisting of a polymer solution reacts with the acid in the surrounding, yielding a water-soluble product. During drop dissolution, water-rich microdroplets form within the drop, merging with the external aqueous phase along the drop-substrate boundary. Two key elements determine the drop rise dynamics. The first is the stick-jump behavior during drop dissolution. The second is that buoyancy exerts a strong enough force on the drop at an Archimedean number greater than 1, while the stick-jump behavior is ongoing. The time of the drop rise is controlled by the initial size and the reaction rate of the drop. This novel mechanism for programmable drop rise may be beneficial for many future applications, such as microfluidics, microrobotics, and device engineering where the spontaneous drop detachment may be utilized to trigger a cascade of events in a dense medium.

Delineating the Effects of Transition-Metal-Ion Dissolution on Silicon Anodes in Lithium-Ion Batteries.

Silicon anode is an appealing alternative to enhance the energy density of lithium-ion batteries due to its high capacity, but it suffers from severe capacity fade caused by its fast degradation. The crossover of dissolved transition-metal (TM) ions from the cathode to the anode is known to catalyze the decomposition of electrolyte on the graphite anode surface, but the relative impact of dissolved Mn2+ versus Ni2+ versus Co2+ on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNi1-x-yMnxCoyO2 (NMC) cathodes and migrate to the anode, here a LiFePO4 cathode is paired with SiOx anode and assess the impact by introducing a specific amount of Mn2+ or Ni2+ or Co2+ ions into the electrolyte. It is found that Mn2+ ions cause a much larger increase in SiOx electrode thickness during cycling due to increased electrolyte decomposition and solid-electrolyte interphase (SEI) formation compared to Ni2+ and Co2+ ions, similar to previous findings with graphite anode. However, with a lower impedance, the SEI formed with Mn2+ protects the Si anode from excessive degradation compared to that with Co2+ or Ni2+ ions. Thus, Mn2+ ions have a less detrimental effect on Si anodes than Co2+ or Ni2+ ions, which is the opposite of that seen with graphite anodes.

Self-Assembly of Silicon Nanotubes Driven by a Biphasic Transition from the Natural Mineral Montmorillonite in Molten Salt Electrolysis.

Silicon nanotubes (SNTs) have been considered as promising anode materials for lithium-ion batteries (LIBs). However, the reported strategies for preparing SNTs generally have special requirements for either expensive templates or complex catalysts. It is necessary to explore a cost-effective and efficient approach for the preparation of high-performance SNTs. In this work, a biphasic transformation strategy involving "solid-state reduction" and "dissolution-deposition" in molten salts is developed to prepare SNTs using montmorillonite as a precursor. The rod-like intermediate of silicon-aluminum-calcium is initially reduced in solid state, which then triggers the continuous dissolution and deposition of calcium silicate in the inner space of the intermediate to form a hollow structure during the subsequent reduction process. The transition from solid to liquid is crucial for improving the kinetics of deoxygenation and induces the self-assembly of SNTs during electrolysis. When the obtained SNTs is used as anode materials for LIBs, they exhibit a high capacity of 2791 mAh g-1 at 0.2 A g-1, excellent rate capability of 1427 mA h g-1 at 2 A g-1, and stable cycling performance with a capacity of 2045 mAh g-1 after 200 cycles at 0.5 A g-1. This work provides a self-assembling, controllable, and cost-effective approach for fabricating SNTs.

A High-Entropy Prussian Blue Analog for Aqueous Potassium-Ion Batteries.

Aqueous potassium-ion batteries (AKIBs) are considered promising electrochemical energy storage systems owing to their high safety and cost-effectiveness. However, the structural degradation resulting from the repeated accommodation of large K-ions and the dissolution of active electrode materials in highly dielectric aqueous electrolytes often lead to unsatisfactory electrochemical performance. This study introduces a high-entropy Prussian blue analog (HEPBA) cathode material for AKIBs, demonstrating significantly enhanced structural stability and reduced dissolution. The HEPBA exhibits a highly reversible specific capacity of 102.4 mAh g-1, with 84.4% capacity retention after undergoing 3448 cycles over a duration of 270 days. Mechanistic insights derived from comprehensive experimental investigations, supported by theoretical calculations, reveal that the HEPBA features a robust structure resistant to dissolution, a solid-solution reaction pathway with negligible volume variation during charge-discharge, and efficient ion transport kinetics characterized by a reduced band gap and a low energy barrier. This study represents a measurable step forward in the development of long-lasting electrode materials for aqueous AKIBs.

In Situ Electrochemical Rapid Induction of Highly Active γ-NiOOH Species for Industrial Anion Exchange Membrane Water Electrolyzer.

Limited by the strong oxidation environment and sluggish reconstruction process in oxygen evolution reaction (OER), designing rapid self-reconstruction with high activity and stability electrocatalysts is crucial to promoting anion exchange membrane (AEM) water electrolyzer. Herein, trace Fe/S-modified Ni oxyhydroxide (Fe/S-NiOOH/NF) nanowires are constructed via a simple in situ electrochemical oxidation strategy based on precipitation-dissolution equilibrium. In situ characterization techniques reveal that the successful introduction of Fe and S leads to lattice disorder and boosts favorable hydroxyl capture, accelerating the formation of highly active γ-NiOOH. The Density Functional Theory (DFT) calculations have also verified that the incorporation of Fe and S optimizes the electrons redistribution and the d-band center, decreasing the energy barrier of the rate-determining step (*O→*OOH). Benefited from the unique electronic structure and intermediate adsorption, the Fe/S-NiOOH/NF catalyst only requires the overpotential of 345 mV to reach the industrial current density of 1000 mA cm-2 for 120 h. Meanwhile, assembled AEM water electrolyzer (Fe/S-NiOOH//Pt/C-60 °C) can deliver 1000 mA cm-2 at a cell voltage of 2.24 V, operating at the average energy efficiency of 71% for 100 h. In summary, this work presents a rapid self-reconstruction strategy for high-performance AEM electrocatalysts for future hydrogen economy.

Seed-Assisted Reversible Dissolution/Deposition of MnO2 for Long-Cyclic and Green Aqueous Zinc-Ion Batteries.

Manganese oxide (MnO2) based aqueous zinc-ion batteries (AZIBs) are considered to be a promising battery for grid-scale energy storage. However, they usually suffer from the great challenge of capacity attenuation due to Mn dissolution and irreversible structural transformation. Herein, full use of the shortcomings is made to design high-performance cathode-free AZIBs. Manganese-based Prussian blue analog (Mn-PBA) is selected as a seed layer to provide a stable MnO2 electrodeposition surface. Thanks to the large specific surface area and manganophilic nature of Mn-PBA, the deposition/dissolution kinetics between Mn2+ and MnO2 are significantly enhanced. Systematic studies revealed the mechanism of MnO2 deposition-dissolution related to the reversible transformation of manganese oxide hydroxide and zinc hydroxide sulfate hydrate. Based on this, the developed cathode-free AZIBs exhibit outstanding rate performance (with a specific capacity of 273.7 mAh g-1 at 1 A g-1) and extraordinary cycle stability (maintaining a specific capacity of 52.3 mAh g-1 after 50 000 cycles at 20 A g-1). Furthermore, the AZIBs with non-toxic, biocompatible materials can be directly discarded after use, without causing pollution to the environment, which is expected to help achieve the sustainable development goals.

High-efficiency Lithium Metal Stabilization and Polysulfide Suppression in Li-S Battery Enabled by Weakly Solvating Solvent.

Lithium-sulfur batteries (LSBs) are considered a highly promising next-generation energy storage technology due to their exceptional energy density and cost-effectiveness. However, the practical use of current LSBs is hindered primarily by issues related to the "shuttle effect" of lithium polysulfide (LiPS) intermediates and the growth of lithium dendrites. In strongly solvating electrolytes, the solvent-derived solid electrolyte interphase (SEI) lacks mechanical strength due to organic components, leading to ineffective lithium dendrite suppression and severe LiPS dissolution and shuttling. In contrast, the weakly solvating electrolyte (WSE) can create an anion-derived SEI layer which can enhance compatibility with lithium metal anode, and restricting LiPS solubility. Herein, a WSE consisting of 0.4 Ð¼ LiTFSI in the mixture of 1,4-dioxane (DX):dimethoxymethane (DMM) is designed to overcome the issues associated with LSB. Surface analyses confirmed the formation of a beneficial SEI layer rich in LiF, enabling homogeneous lithium deposition with an average Coulombic efficiency CE exceeding 99% over 100 cycles. Implementing the low-concentration WSE in Li||SPAN cells yielded an impressive initial specific capacity of 671 mAh g-1. This research highlights the advantages of WSE and offers the pathway for cost-effective electrolyte development, enabling the realization of high-performance LSBs.