Ion Transport Characteristics Research Articles

Oxygen ion diffusion in RE3TaO7: Why long-range migration of O2− is prohibited in the defective-fluorite structure?

Oxides with low O2− lattice diffusion rate are critical for the development of topcoat materials for next generation thermal barrier coatings (TBCs) working at > 1600 °C to prevent the fast growth of thermally grown oxide (TGO) at the bondcoat/topcoat interface. Here we delve into a comprehensive analysis of the oxygen ion transport characteristics of the recently developed low-, medium- and high-entropy rare earth tantalates (RE3TaO7) for TBCs by a combination of impedance spectroscopy, 18O isotope diffusion tests and atomic-scale simulations. Results show that the RE3TaO7 series display remarkably low oxygen ion diffusion rate (> 3 orders of magnitude lower than the state-of-the-art topcoat material yttria stabilized zirconia, YSZ) despite the presence of abundant oxygen vacancies in the structure. Molecular dynamic (MD) simulations combined with first principles calculations reveal that oxygen ions are strongly trapped by the potential well at the Ta-Ta edge in the tantalates. In addition, the high electrostatic potential (EP) surrounding oxygen vacancies and the high diffusion barriers between rare earth elements also impede oxygen ion diffusion. With low oxygen ion diffusion rate, along with exceptional thermal and mechanical properties reported previously, RE3TaO7 are promising topcoat materials for next-generation TBCs working at higher temperatures. Moreover, this study also provides valuable insights for understanding the O2− lattice diffusion behaviour in RE3TaO7 with a defective fluorite structure, which may benefit the exploration of oxide-ion conductors.

Water and Chloride Ion Transport Characteristics of Unsaturated Aeolian Sand Mortar under Capillary Absorption

Water and Chloride Ion Transport Characteristics of Unsaturated Aeolian Sand Mortar under Capillary Absorption

(Invited) Understanding Mechanisms of Ion and Electron Transport in Reconfigurable Electrochemical Neuromorphic Components

New materials are emerging as promising components of reconfigurable electrochemical random access memory devices. Among them, transition metal oxides such as those containing vanadium, tantalum, titanium, have shown interesting behaviors regarding their abilities to emulate neuronal behavior, including synapses and other neuronal conductance characteristics, which make them potential candidate components for neuromorphic analog computing devices. In parallel, materials based on molecular complexes appear as another set of promising components that suitably arranged as molecular films may yield artificial neuronal behavior. Here we analyze the ion and electron transport characteristics in these two sets of materials and discuss the fundamental physical and chemical aspects that may drive targeted conductance and memory retention properties. Using first principles theory and simulations we highlight similarities and differences between these two sets of materials regarding their conductance properties and neuromorphic behavior.

In Situ Visualization of Ion Transport Processes in Aqueous Batteries.

Aqueous rechargeable batteries are regarded as one of the most reliable solutions for electrochemical energy storage, and ion (e.g., H+ or OH-) transport is essential for their electrochemical performance. However, modeling and numerical simulations often fall short of depicting the actual ion transport characteristics due to deviations in model assumptions from reality. Experimental methods, including laser interferometry, Raman, and nuclear magnetic resonance imaging, are limited by the complexity of the system and the restricted detection of ions, making it difficult to detect specific ions such as H+ and OH-. Herein, in situ visualization of ion transport is achieved by innovatively introducing laser scanning confocal microscopy. Taking neutral Zn-air batteries as an example and using a pH-sensitive probe, real-time dynamic pH changes associated with ion transport processes are observed during battery operation. The results show that after immersion in the zinc sulfate electrolyte, the pH near the Zn electrode changes significantly and pulsation occurs, which demonstrates the intense self-corrosion hydrogen evolution reaction and the periodic change in the reaction intensity. In contrast, the change in the pH of the galvanized electrode plate is weak, proving its significant corrosion inhibition effect. For the air electrode, the heterogeneity of ion transport during the discharging and charging process is presented. With an increase of the current density, the ion transport characteristics gradually evolve from diffusion dominance to convection-diffusion codominance, revealing the importance of convection in the ion transport process inside batteries. This method opens up a new approach of studying ion transport inside batteries, guiding the design for performance enhancement.

Automated Scanning Dielectric Microscopy Toolbox for Operando Nanoscale Electrical Characterization of Electrolyte‐Gated Organic Transistors

AbstractElectrolyte‐gated organic transistors (EGOTs) leveraging organic semiconductors' electronic and ionic transport characteristics are the key enablers for many biosensing and bioelectronic applications that can selectively sense, record, and monitor different biological and biochemical processes at the nanoscale and translate them into macroscopic electrical signals. Understanding such transduction mechanisms requires multiscale characterization tools to comprehensively probe local electrical properties and link them with device behavior across various bias points. Here, an automated scanning dielectric microscopy toolbox is demonstrated that performs operando in‐liquid scanning dielectric microscopy measurements on functional EGOTs and carries out extensive data analysis to unravel the evolution of local electrical properties in minute detail. This paper emphasizes critical experimental considerations permitting standardized, accurate, and reproducible data acquisition. The developed approach is validated with EGOTs based on blends of organic small molecule semiconductor and insulating polymer that work as accumulation‐mode field‐effect transistors. Furthermore, the degradation of local electrical characteristics at high gate voltages is probed, which is apparently driven by the destruction of local crystalline order due to undesirable electrochemical swelling of the organic semiconducting material near the source electrode edge. The developed approach paves the way for systematic probing of EGOT‐based technologies for targeted optimization and fundamental understanding.

Effect of Membrane Thickness on Ion Transport in pH-Regulated Zero-Depth Interfacial Nanopores.

Zero-depth interfacial nanopores, which are formed by two crossed nanoscale channels at their intersection interface, have been proposed to increase the spatial resolution of solid-state nanopores. However, research on zero-depth interfacial nanopores is still in its early stages. Although it has been shown that the current passing through an interfacial nanopore is largely independent of the membrane thickness, existing studies have not fully considered the impact of membrane thickness on other ion transport characteristics within these nanopores. In this paper, we investigate the electrokinetic ion transport phenomenon in the zero-depth interfacial nanopores, especially focusing on the influence of membrane thickness on the ion transport phenomenon. Our model incorporates the Poisson-Nernst-Planck equations and the Navier-Stokes equations, featuring a pH-regulated surface charge density. We find that when the thickness of the nanochannels is close to the interface size of the formed interfacial nanopore, the phenomenon of ion transport in the interfacial nanopore is similar to that in a conventional cylindrical nanopore. However, when the thickness of the nanochannels is much greater than the interface size of the formed interfacial nanopore, several distinct phenomena occur. The surface charge density on the inner walls of the interfacial nanopores has a small peak at the interface of the two crossing nanochannels, and the anion concentration changes greatly between the two nanochannels; that is, a much greater anion concentration forms in the nanochannel near the anode side than in the nanochannel near the cathode side. When the surface charge is nonzero, the electric field within the interfacial nanopore creates three extreme points, and the directions of the local electric fields are opposite at the ends of the membrane.

Large‐Area Graphene‐Based Ion‐Selective Membranes with Micro/Meso‐Pores for Osmotic Energy Harvesting

AbstractRenewable osmotic energy between seawater and river water shows great potential in meeting global energy demand. Reverse electrodialysis (RED) technique using ion‐selective membrane is particularly outstanding for its easy operation. Preparing low‐cost and large‐area ion‐selective membranes with excellent ion transport characteristics is particularly important to promote commercial applications. Herein, large‐area ion‐selective membrane is prepared by scraping slurry of flocculated GO (graphene oxide)/PAAS (sodium polyacrylate) solution and then coated with PVA (polyvinyl alcohol)/SA (sodium alginate) gel layer. The PVA/SA molecules can penetrate into the membrane through the unique micro/meso‐pores, which together increase the ion selectivity, membrane permeability, and stability. This ion‐selective membrane can achieve a power density of 8.65 W m−2 under a 50‐fold salinity gradient (NaCl) simulating the sea/river junction environment (with the testing area of 0.0314 mm2). This work significantly promotes the application of GO in large‐area preparation of low‐cost ion‐selective membrane.

Solid-state synthesis and ion transport characteristics of the β-KSbF4 for all-solid-state fluoride-ion batteries

All-solid-state fluoride ion batteries (FIBs) have been recently considered as a post-lithium-ion battery system due to their high safety and high energy density. Just like all solid-state lithium batteries, the key to the development of FIBs lies in room-temperature electrolytes with high ionic conductivity. β-KSbF4 is a kind of promising solid-state electrolyte for FIBs owing to its rational ionic conductivity and relatively wide electrochemical stability window at room temperature. However, the previous synthesis routes of β-KSbF4 required the use of highly toxic hydrofluoric acid and the ionic conductivity of as-prepared product needs to be further improved. Herein, the β-KSbF4 sample with an ionic conductivity of 1.04 × 10−4 S cm−1 (30 °C) is synthesized through the simple solid-state route. In order to account for the high ionic conductivity of the as-synthesized β-KSbF4, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) are used to characterize the physicochemical properties. The results show that the as-synthesized β-KSbF4 exhibits higher carrier concentration of 1.0 × 10−6 S cm−1 Hz−1 K and hopping frequency of 1.31 × 106 Hz at 30 °C due to the formation of the fluorine vacancies. Meanwhile, the hopping frequency shows the same trend as the changes of ionic conductivity with the changes of temperature, while the carrier concentration is found to be almost constant. The two different trends indicate the hopping frequency is mainly responsible for the ionic conduction behavior within β-KSbF4. Furthermore, the all-solid-state FIBs, in which Ag and Pb + PbF2 are adopted as cathode and anode, and β-KSbF4 as fluoride ion conductor, are capable of reversible charge and discharge. The assembled FIBs show a discharge capacity of 108.4 mA h g−1 at 1st cycle and 74.2 mA h g−1 at 50th cycle. Based on an examination of the capacity decay mechanism, it has been found that deterioration of the electrolyte/electrode interface is an important reason for hindering the commercial application of FIBs. Hence, the in-depth comprehension of the ion transport characteristics in β-KSbF4 and the interpretation of the capacity fading mechanism will be conducive to promoting development of high-performance FIBs.

A Review of Durability of New and Old Concrete Joints

The purpose of this study is to explore the durability of the new and old concrete joints, including chloride ion erosion, freeze-thaw phenomena, and the influence of aggregates. Firstly, taking into account the difference in material properties between the old and new concrete, this study analyzes the chloride ion transport characteristics of the joints in detail, focusing on the key areas of the joints, that is, the areas where the old concrete may have been eroded by chloride ions. Secondly, this study explores the change in the properties of the joints under freeze-thaw conditions, and the influence of different interface treatment methods on the properties of the joints. Finally, this study examines the influence of the type and content of aggregates on the durability of the joints. Through the above research, this paper aims to provide some useful guidance and suggestions for the durability design of the old and new concrete structures.

Exploring steric and electronic effects in tailoring lithium-ion solvation using engineered ether solvents through molecular dynamics simulations

Lithium-metal batteries, owing to their remarkable energy density, represent a promising solution for future energy storage needs. However, the widespread adoption of lithium-metal batteries has been impeded by the inherent instability that exists between lithium metal and traditional liquid lithium electrolytes, initially designed for graphite anodes in lithium-ion batteries. Recent insights underscore the efficacy of electrolyte engineering as a strategic avenue to realize the potential of lithium-metal batteries. A notable approach involves the fluorination of solvent molecules, particularly those of the ether class. Nonetheless, a comprehensive understanding of the various factors governing solvent molecular design remains elusive. Here, we examine four solvents derived from 1,2-dimethoxylethane (DME) via molecular dynamics simulation. These solvents are engineered with the introduction of additional alkyl groups or through fluorination. We particularly scrutinize two critical facets: steric effects, arising from the incorporation of bulkier alkyl chains, and electronic effects, originating from fluorination. Our inquiry delves deeply into the stability, ion transport characteristics, and solvation behavior exhibited by these five distinct solvents. Our study underscores the profound impact of adjusting the steric and electronic attributes of solvent molecules on Li+ solvation behavior. This, in turn, influences the coordination strength and the mode of association between Li+ and solvation sites within the first solvation shell, providing key insights into the disparities in ion transport properties within electrolytes.

Insight into the Improvement Strategies of Aqueous Electrolyte for Aqueous Rechargeable Batteries

AbstractAqueous rechargeable batteries (ARBs) have attracted wide attention due to their rich resources, environmental friendliness, and safety. The high ionic conductivity, safety and interfacial wettability of the aqueous electrolyte are essential for energy storage devices. However, the narrow electrochemical stability window (ESW) of the aqueous electrolyte and the side reactions of the electrode/electrolyte lead to the low energy density of the ARBs. In the past studies, the above problems were generally solved by improving the ion transport characteristics of the electrolyte and the electrode/electrolyte interface. Herein, we discuss the background, limitations, and key concepts for performance improvement of aqueous electrolytes, aiming to provide a comprehensive perspective and inspiration for further research on aqueous electrolytes and promote their development and application in the field of energy storage.

Enhancement of ionic transport characteristics and cell performance through multi-layered separator microstructure in Li-ion cells

Enhancement of ionic transport characteristics and cell performance through multi-layered separator microstructure in Li-ion cells

Polyethylene glycol-decorated n-type conducting polymers with improved ion accessibility for high-performance organic electrochemical transistors.

High-performance n-type organic mixed ionic-electronic conductors (OMIECs) are essential for advancing complementary circuits based on organic electrochemical transistors (OECTs). Despite significant progress, current n-type OMIECs often exhibit lower transconductance and slower response times compared to their p-type counterparts, limiting the development of OECT-based complementary circuits. Optimizing the conjugated backbone and side chain structures of OMIECs is critical for enhancing both ion and electron transport efficiencies while maintaining a delicate balance between the two. In this study, hydrophilic polyethylene glycol (PEG) side chains were incorporated into the highly conductive n-type polymer poly(3,7-dihydrobenzo[1,2-b:4,5-b']difuran-2,6-dione) (PBFDO) backbone to achieve this goal. The incorporation of PEG chains improved ion accessibility, and by adjusting the PEG content, the electronic and ionic transport properties were fine-tuned, ultimately enhancing the performance of OECTs and related p-n complementary circuits. The n-type OECTs based on PBFDO-PEG50wt% demonstrated exceptional transfer characteristics, including a transient response time (τON) as low as 72 μs, a high geometry-normalized transconductance exceeding 400 S cm-1, and an impressive μC* value surpassing 720 F cm-1 V-1 s-1. Notably, the use of PBFDO-PEG50wt% in a complementary inverter resulted in a voltage gain of 20 V/V, more than five times higher than that achieved with unmodified PBFDO (<4 V/V). These findings highlight the importance of balancing electron and ion transport characteristics in OMIECs to achieve high performance in OECTs and their associated circuits, and they validate PEG decoration as an effective approach.

Randomness and time-varying characteristics of chloride ion transport in existing harbor concrete structures

This paper presents a study on the durability testing of a concrete facility located within the North Bay Port region, which has been in service for 200 months. Based on the results of 20 sets of concrete samples, an improved Kolmogorov-Smirnov (K-S) test method and gross error discrimination method are proposed to analyze the random distribution functions of the apparent chloride diffusion coefficient (Dapp) and the apparent surface chloride concentration (Cs), and further explore the time-varying characteristics of chloride ion transmission in concrete. The research shows that the improved K-S method presented in this paper can effectively reduce the probability of type II errors by selecting a rational sample size, which can also improve detection efficiency. When the sample size does not exceed 10, the 2σ criterion proposed in this paper can effectively identify and eliminate gross errors. In general, Dapp and Cs follow the log-normal distribution, while the time factor (m) follows a normal distribution parameter. The value of Cs basically stabilized after exposure to 80 months, whereas Dapp tended to stabilize after exposure to 100 months. The value of m obtained through fitting short-term experimental data is typically overestimated, and its value decreases as the exposure time prolongs. Therefore, m should also be considered a time-varying parameter that decreases with time. The tested RC structure will begin to experience rebar corrosion after 48.5-60 years of exposure to the marine environment based on the probabilistic assessment.

Ion transport mechanisms in pectin-containing EC-LiTFSI electrolytes.

Using all-atom molecular dynamics simulations, we report the structure and ion transport characteristics of a new class of solid polymer electrolytes that contain the biodegradable and mechanically stable biopolymer pectin. We used highly conducting ethylene carbonate (EC) as a solvent for simulating lithium-trifluoromethanesulfonimide (LiTFSI) salt containing different weight percentages of pectin. Our simulations reveal that the pectin chains reduce the coordination number of lithium ions around their counterions (and vice versa) because of stronger lithium-pectin interactions compared to lithium-TFSI interactions. Furthermore, the pectin is found to promote smaller ionic aggregates over larger ones, in contrast to the results typically reported for liquid and polymer electrolytes. We observed that the loading of pectin in EC-LiTFSI electrolytes increases their viscosity (η) and relaxation timescales (τc), indicating higher mechanical stability, and, consequently, a decrease of the mean squared displacement, diffusion coefficient (D), and Nernst-Einstein conductivity (σNE). Interestingly, while the lithium diffusivities are related to the ion-pair relaxation timescales as D+ ∼ τc-3.1, the TFSI- diffusivities exhibit excellent correlations with ion-pair relaxation timescales as D- ∼ τc-0.95. On the other hand, the NE conductivities are dictated by distinct transport mechanisms and scales with ion-pair relaxation timescales as σNE ∼ τc-1.85.

Effects of Restoration Strategies on the Ion Distribution and Transport Characteristics of Medicago sativa in Saline–Alkali Soil

Studying the distribution and transport dynamics of cations in plants is crucial for understanding their response mechanisms to saline–alkali stress conditions. However, our current understanding of how restoration measures affect cation distribution and transport in plants is surprisingly limited. To address this gap, we conducted a split-plot experiment using Medicago sativa L. cv. “Zhongmu No. 1” to investigate the combined effects of biological and chemical restoration measures—with bio-fertilizer as the primary zone and flue gas desulfurization (FGD) gypsum and with humic acid as the secondary zone—on soil properties, plant growth, and the content, distribution, and transport of cations in plants. The results revealed that bio-fertilizers exhibited positive effects on the plant growth, yield, and translocation of key ionic components to leaves. On the contrary, FGD gypsum with humic acid reduced the soil’s pH level, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) while increasing the contents of K+, Ca2+, and Mg2+ in the soil. The combination of bio-fertilizer, FGD gypsum, and humic acid increased the biomass and enhanced the translocation of Mg2+ to leaves. The distribution and transport of Mg2+ within the plant constituted pivotal elements for enhancing plant growth through restoration strategies. The application of bio-fertilizer, FGD gypsum, and humic acid reduced Na+ transport in M. sativa by enhancing the selective absorption of beneficial ions in leaves and by facilitating the transport of Ca2+ and Mg2+ from stems to the leaves. This, in turn, increases the salt tolerance of plants and promotes their growth. Our results offer new insights into the interactions among measures, soil, and plants in saline–alkali land restoration, providing practical solutions for the restoration of saline–alkali soil.

Selective and asymmetric ion transport in covalent organic framework-based two-dimensional nanofluidic devices

ABSTRACT Two-dimensional (2D) covalent organic framework (COF) membranes featuring well-aligned and programmable vertical nanochannels have emerged as a promising candidate for advanced nanofluidic devices and showcased vast potential in the fields of smart-gating, ion-separation, and energy-harvesting. However, the transverse interlayer nanochannels with a height of sub-nanometer-scale in 2D-COF membranes have scarcely been studied in comparison. Here, we report the ion transport characteristics in 2D interlayer nanochannels of protonated COF membranes. The distinct surface-charge-governed ionic conductance in domination of electrolyte concentration below 10−3 M as well as the exceptional anion/cation (Cl−/K+) selectivity is revealed due to the pronounced charge and nano-confinement effects. Additionally, evident ion current rectification is witnessed when incorporating asymmetric geometry into the system, which is attributed to the dynamic process of ion enrichment and dissipation within the protonated nanochannels. This work offers immense prospects for 2D-COF membranes in the fields of biomimetic nanofluidic devices and cutting-edge electronic devices.

Ion Transport in Intelligent Nanochannels: A Comparative Analysis of the Role of Electric Field.

This research delves into investigating ion transport behavior within nanochannels, enhanced through modification with a negatively charged polyelectrolyte layer (PEL), aimed at achieving superior control. The study examines two types of electric fields─direct current and alternating current with square, sinusoidal, triangular, and sawtooth waveforms─to understand their impact on ion transport. Furthermore, the study compares symmetric (cylindrical) and asymmetric (conical) nanochannel geometries to assess the influence of overlapping electrical double layers (EDLs) in generating specific electrokinetic behaviors such as ionic current rectification (ICR) and ion selectivity. The research employs the finite element method to solve the coupled Poisson-Nernst-Planck and Navier-Stokes equations under unsteady-state conditions. By considering factors such as electrolyte concentration, soft layer charge density, and electric field type, the study evaluates ion transport performance in charged nanochannels, investigating effects on concentration polarization, electroosmotic flow (EOF), ion current, rectification, and ion selectivity. Notably, the study accounts for ion partitioning between the PEL and electrolyte to simulate real conditions. Findings reveal that conical nanochannels, due to improved EDL overlap, significantly enhance ion transport and related characteristics compared to cylindrical ones. For instance, under ηε = ηD = 0.8, ημ = 2, C0 = 20 mM, and NPEL/NA = 80 mol m-3 conditions, the average EOF for conical and cylindrical geometries is 0.1 and 0.008 m/s, respectively. Additionally, the study explores ion selectivity and rectification based on the electric field type, unveiling the potential of nanochannels as ion gates or diodes. In cylindrical nanochannels, the ICR remains at unity, with lower ion selectivity across waveforms compared to conical channels. Furthermore, rectification and ion selectivity trends are identified as Rf,square > Rf,DC > Rf,triangular > Rf,sinusoidal > Rf,sawtooth and Ssawtooth > Ssinusoidal > Striangular > SDC > Ssquare for conical nanochannels. Our study of ion transport control in nanochannels, guided by tailored electric fields and unique geometries, offers versatile applications in the field of Analytical Chemistry. This includes enhanced sample separation, controlled drug delivery, optimized pharmaceutical analysis, and the development of advanced biosensing technologies for precise chemical analysis and detection. These applications highlight the diverse analytical contributions of our methodology, providing innovative solutions to challenges in chemical analysis and biosensing.

Physical vapor deposition of Sb2Se3 films as high-performance anode materials in quasi-solid-state Li-ion batteries

Antimony selenide (Sb2Se3) thin films with cluster morphology were prepared using physical vapor deposition method combined with the post-annealing process. The composition and morphology of the prepared films were characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical analysis of the samples revealed that the Li/Sb2Se3 half-cell exhibited an initial discharge specific capacity of 825.7 mAh∙g−1 at a current density of 0.5 C, and a discharge specific capacity of 1192.7 mAh∙g−1 after 100 charge-discharge cycles. The Sb2Se3 film also displayed excellent rate characteristics and a high cycling performance with a high discharge specific capacity of 812.2 mAh∙g−1 at current density of 2 C after 600 charge-discharge cycles. Results obtained from the galvanostatic intermittent titration tests and from electrochemical impedance spectroscopy proved that the cluster structure of the thin film was beneficial to the ion transport characteristics, as well as for the rate performance of the Sb2Se3 thin film materials. A quasi-solid-state battery based on Sb2Se3/Li1.3Al0.3Ti1.7(PO4)3/LiFePO4 was also assembled, which provided a discharge specific capacity of 445.5 mAh∙g−1 at 0.5 C with a capacity retention rate of 49.7% after 200 charge-discharge cycles. The results of this study clearly suggest that the use of Sb2Se3 films as anode materials can provide promising results in the performance enhancement of quasi-solid-state Li-ion batteries.

Stray current induced chloride ion transport and corrosion characteristics of cracked ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a strong, durable, and corrosion-resistant material that is poised to revolutionize construction in complex environments, such as the deep sea and underground. However, the formation of cracks of UHPC during service and the occurrence of stray currents in underground stations and tunnels greatly accelerate the transport of chloride ions, posing a threat to the safety of underground construction. Here, we used the rapid chloride migration (RCM) method to study the effect of stray current in cracked UHPC. Essentially, electric field accelerates chloride ion transport in cracks by increasing ion transport in the uncracked zone. The wider the crack, the more severe the corrosion of steel fibers, which affects the pore structure of UHPC and leads to an increase in the diffusion coefficient in the uncracked area. In addition, area normalization was employed to precisely monitor the chloride ion concentration in the cracks, which was validated by numerical simulations. Finally, microscopy and atomic force microscopy (AFM) showed that larger crack widths led to deeper corrosion and more severe steel fiber corrosion in UHPC. These results have important implications for the durability design of UHPC structures in stray current environments.