Electrolyte Transport Research Articles

Dynamics of Gas Generation in Porous Electrode Alkaline Electrolysis Cells: An Investigation and Optimization Using Machine Learning

This paper presents a systematic and comprehensive mathematical model for alkaline water electrolyzer cells, which can be used for simulation and analysis. The model accounts for factors such as gas evolution reactions, dissolution of gases in the electrolyte, bubble formation, and charge transport. It is based on a numerical two-phase model using the Euler-Euler approach, which has been validated against experimental data for various current densities. The study compares the impact of varying potassium hydroxide (KOH) concentration, separator porosity, and electrolyte flow rates on two-phase flow and bubble coverage. Therefore, the electrolyte in the cell consists of a solution of potassium hydroxide in water. The formation of gas bubbles at the electrodes decreases the electrolyte’s ionic conductivity. Additionally, the presence of these bubbles on the electrode surfaces reduces the available surface area for electrochemical reactions, leading to an increase in the overpotential at a given current density. Furthermore, this paper demonstrates how a neural network and ensembled tree model can predict hydrogen production rates in an alkaline water electrolysis process. The trained neural network accurately predicted the hydrogen production rates, indicating the potential of using neural networks for optimization and control of alkaline water electrolysis processes. The model has an average R-squared value of 0.98, indicating a good fit to the data. A new method of describing bubble transfer, “bubble diffusion,” is introduced to improve performance and reduce costs. The model is solved using COMSOL Multi physics 6.0. The machine learning models in this study were built, trained, and tested using MATLAB software R2020a.

Insight into LIB Diffusion Phenomena Using Analytical Impedance Models

Electrochemical impedance spectroscopy (EIS) is extensively used to characterize the transport properties in porous electrodes of lithium-ion batteries (LIB). In the low-frequency domain (f < 1 Hz), solid diffusion and electrolyte diffusion are competing over similar timescales, which explains why both phenomena are difficult to characterize independently. In which case can the solid diffusion coefficient be correctly extracted from experimental EIS? To answer this question, the linearized P2D-Newman model of a complete cell is solved using a Fourier transform to obtain a physics-based analytical impedance. The solution allows deriving the characteristic frequencies and non-dimensional numbers of the system, and gives the parameters range for which solid diffusion is overwhelming electrolyte transport in the impedance signal. A simple criterion is then given to discriminate electrodes that are properly designed for active materials electrochemical characterization.

Time to eRAASe chronic inflammation: current advances and future perspectives on renin-angiotensin-aldosterone-system and chronic intestinal inflammation in dogs and humans.

Chronic idiopathic intestinal inflammation is an increasing worldwide problem that affects companion animals, especially dogs, and human patients. Although these disease entities have been intensely investigated recently, many questions remain, and alternative therapeutic options are needed. Diarrhea caused by dysregulation of intestinal electrolyte transport and subsequent fluid and electrolyte losses often leads to secondary consequences for the patient. Currently, it is not exactly clear which mechanisms are involved in the dysregulation of intestinal fluid absorption, but differences in intestinal electrolyte shifts between human and canine patients suggest species-specific regulatory or counterregulatory mechanisms. Several intestinal electrolyte transporters are differentially expressed in human patients with inflammatory bowel disease (IBD), whereas there are virtually no studies on electrolyte transporters and their endocrine regulation in canine chronic inflammatory enteropathy. An important mechanism involved in regulating fluid and electrolyte homeostasis is the renin-angiotensin-aldosterone-system (RAAS), which may affect intestinal Na+ transport. While RAAS has previously been considered a systemic regulator of blood pressure, additional complex roles of RAAS in inflammatory processes have been unraveled. These alternative RAAS pathways may pose attractive therapeutic targets to address diarrhea and, thus, electrolyte shifts in human IBD and canine chronic inflammatory enteropathy. This article comparatively summarizes the current knowledge about electrolyte transport in human IBD and canine chronic inflammatory enteropathy and the role of RAAS and offers perspectives for novel therapeutic avenues.

Vertical and porous MoS2-CoS2 heterojunction nanosheet arrays as highly efficient bifunctional electrocatalysts for oxygen and hydrogen evolutions

Highly efficient water electrolytic agents are restricted by the lack of cheap and Earth-abundant catalysts that can manipulate at unharsh conditions and be prepared with a simple procedure. Here, hierarchically vertical and porous MoS2-CoS2 heterojunction nanosheet arrays are designed and fabricated. The MoS2-CoS2 nanosheets are composed of ultrasmall nanocrytallites with the dimension of ∼62 nm. This special and novel architecture presents synergistic properties to create excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), where high density active sites generated by ultrasmall nanocrytallites with heterostructures, and the vertical and porous structure accelerates electrolyte transport with luxuriant channels while this hierarchically collaborative framework guarantees completely exposed active sites to electrolytes. This electrode shows low overpotentials of 295 and 103 mV at 10 mA cm−2, small Tafel slopes of 70 and 78 mV dec−1, and long stability for OER and HER, respectively. This work indicates that vertical and porous heterojunction nanosheet arrays with hierarchically ultrasmall secondary nanostructures are a promising catalyst for widespread application.

Fundamental investigations on the ionic transport and thermodynamic properties of non-aqueous potassium-ion electrolytes

Non-aqueous potassium-ion batteries (KIBs) represent a promising complementary technology to lithium-ion batteries due to the availability and low cost of potassium. Moreover, the lower charge density of K+ compared to Li+ favours the ion-transport properties in liquid electrolyte solutions, thus, making KIBs potentially capable of improved rate capability and low-temperature performance. However, a comprehensive study of the ionic transport and thermodynamic properties of non-aqueous K-ion electrolyte solutions is not available. Here we report the full characterisation of the ionic transport and thermodynamic properties of a model non-aqueous K-ion electrolyte solution system comprising potassium bis(fluorosulfonyl)imide (KFSI) salt and 1,2-dimethoxyethane (DME) solvent and compare it with its Li-ion equivalent (i.e., LiFSI:DME), over the concentration range 0.25–2 molal. Using tailored K metal electrodes, we demonstrate that KFSI:DME electrolyte solutions show higher salt diffusion coefficients and cation transference numbers than LiFSI:DME solutions. Finally, via Doyle-Fuller-Newman (DFN) simulations, we investigate the K-ion and Li-ion storage properties for K∣∣graphite and Li∣∣graphite cells.

Ionic transport in solid-state composite poly(trimethylene carbonate)–Li6.7Al0.3La3Zr2O12 electrolytes: The interplay between surface chemistry and ceramic particle loading

The ionic transport in solid-state composite electrolytes based on poly(trimethylene carbonate) (PTMC) with LiTFSI salt and garnet-type ion-conducting Li6.7Al0.3La3Zr2O12 (LLZO) ceramic particles is here investigated for a range of different compositions. Positive effects on ionic conductivity have previously been reported for LLZO incorporated into poly(ethylene oxide) (PEO), but the origin of these effects is unclear since the inclusion of particles also affects polymer crystallinity. PTMC is, in contrast to PEO, a fully amorphous polymer, and therefore here chosen for the design of a more straight-forward composite electrolyte (CPE) system to study ionic transport. With LLZO loadings ranging from 5 to 70 wt%, the CPE with 30 wt% of LLZO exhibits the highest ionic conductivity with a cationic transference number of 0.94 at 60 °C. This is significantly higher than for the pristine PTMC polymer electrolyte. Generally, low to moderate LLZO loadings display a gradual increase of the ionic conductivity, transference number and also of the polymer-cation coordination number. The combined contributions of ionic transport along polymer-ceramic interfaces and Lewis acid-base interaction between the LLZO particles and the LiTFSI salt can explain this enhancement. With loadings of LLZO above 50 wt%, a detrimental effect on the ionic conductivity was however observed. This could be explained by agglomeration of ceramic particles, and by a partial coverage of LLZO particles with a Li2CO3 layer. Consequently, inner polymer-particle interfaces become more resistive, and Li+conduction is prevented along interfacial pathways. The presence of Li2CO3 has more detrimental impact at higher LLZO loadings, since inter-particle connectivity will be hampered, and this is vital for efficient ionic transport. This suggests that there is an interplay between the LLZO particle surface chemistry with its loading, which ultimately controls the Li-ion transport.

Li-Ion Transport and Solution Structure in Sulfolane-Based Localized High-Concentration Electrolytes

Localized high-concentration electrolytes (LHCEs), which are mixtures of highly concentrated electrolytes (HCEs) and non-coordinating diluents, have attracted significant interest as promising liquid electrolytes for next-generation Li secondary batteries, owing to their various beneficial properties both in the bulk and at the electrode/electrolyte interface. We previously reported that the large Li+-ion transference number in sulfolane (SL)-based HCEs, attributed to the unique exchange/hopping-like Li+-ion conduction, decreased upon dilution with the non-coordinating hydrofluoroether (HFE) despite the retention of the local Li+-ion coordination structure. Therefore, in this study, we investigated the effects of HFE dilution on the Li+ transference number and the solution structure of SL-based LHCEs via the analysis of dynamic ion correlations and molecular dynamics simulations. The addition of HFE caused nano-segregation in the SL-based LHCEs to afford polar and nonpolar domains and fragmentation of the polar ion-conducting pathway into smaller clusters with increasing HFE content. Analysis of the dynamic ion correlations revealed that the anti-correlated Li+–Li+ motions were more pronounced upon HFE addition, suggesting that the Li+ exchange/hopping conduction is obstructed by the non-ion-conducting HFE-rich domains. Thus, the HFE addition affects the entire solution structure and ion transport without significantly affecting the local Li+-ion coordination structure. Further studies on ion transport in LHCEs would help obtain a design principle for liquid electrolytes with high ionic conductivity and large Li+-ion transference numbers.

Polymer Chain‐Guided Ion Transport in Aqueous Electrolytes of Zn‐Ion Batteries

AbstractAs a promising candidate for next‐generation energy storage devices, Zn metal battery excels with their good safety, high specific capacity, and economic attractiveness. However, it still suffers from a narrow electrochemical window, notorious dendrite formation, and sluggish Zn ion transfer. Aqueous electrolyte engineering has been regarded as an effective way to improve these. It is shown that by adding sodium polystyrene sulfonate (PSS) polymers into a dilute 1 m Zn(OTf)2 aqueous electrolyte, compact water shells with stronger hydrogen bonding and more ordered structures are formed around the polymer chains. As a result, a fast transport channel to the zinc ions is provided. The PSS chains also protect the zinc electrode from directly contacting the water molecules and thus suppress water decomposition. With these merits, a Zn//Cu cell demonstrates a high coulombic efficiency of ≈99% after 1500 h cycling. Meanwhile, a record‐high cumulative Zn plating capacity of 10 000 mA h cm−2 is obtained using a Zn||Zn cell. In addition, the Zn//C@V2O5 full cell achieves almost 100% capacity retention after 1000 cycles. This work provides a new strategy for designing advanced electrolyte systems excelling in ion transport kinetics.

Hydrogen Bonding Induced Confinement Effect between Ultrafine Nanowires and Polymer Chains for Low-Energy-Barrier Ion Transport in Composite Electrolytes.

Achieving low-energy-barrier lithium ion transport is a fundamental issue for composite solid-state electrolytes (CSEs) in all-solid-state lithium metal batteries (ASSLMBs). In this work, a hydrogen bonding induced confinement strategy was proposed to construct confined template channels for low-energy-barrier lithium ion continuous transport. Specifically, the ultrafine boehmite nanowires (BNWs) with 3.7 nm diameter were synthesized and superiorly dispersed in a polymer matrix to form a flexible CSE. The ultrafine BNWs with large specific surface areas and abundant oxygen vacancies assist the dissociation of lithium salts and confine the conformation of polymer chain segments by hydrogen bonding between the BNWs and the polymer matrix, thus forming a polymer/ultrafine nanowire intertwined structure as template channels for dissociated lithium ions continuous transport. As a result, the as-prepared electrolytes displayed a satisfactory ionic conductivity of 0.714 mS cm-1 and low energy barrier (16.30 kJ mol-1), and the assembled ASSLMB delivered excellent specific capacity retention (92.8%) after 500 cycles. This work demonstrates a promising way to design CSEs with high ionic conductivity for high-performance ASSLMBs.

Protonated chitosan nanostructures for enhancing ionic conductivity of solid-state electrolytes

Solid polymer electrolytes (SPEs) have aroused widespread attention for their high flexibility and good interface contact with electrode. However, the low ionic conductivity severely hinders their application in energy storage devices. Herein, a novel protonated nanostructure was synthesized through the reaction between PEO and Chitosan (Chi) and applied as fillers to form PEO/Chi composite solid-state electrolytes (PCCSEs). The fillers, which achieve nanization by the reaction with PEO, plays an important role in promoting the property of transporting Li+, due to the protonated amino (–NH3+) improving the dissociation of LiTFSI and the nanoscale size with high dispersity. Various characterizations and density functional theory (DFT) calculations were applied to reveal the enhanced Li+ transport mechanism in PCCSE. Owing to the unique design, PCCSE exhibits excellent ionic conductivity at room temperature (1.02 × 10−4 S cm−1) and the Li||SSEs||Li symmetric cells and LFP||SSEs||Li batteries with PCCSE show great cycling stability. This strategy of taking full use of the cations in protonated Chi provides effective design guidance for promoting the Li+ transport in polymer-based electrolytes.

Homogenization of the linearized ionic transport equations in random porous media

In this paper we obtain the homogenization results for a system of partial differential equations describing the transport of a N-component electrolyte in a dilute Newtonian solvent through a rigid random disperse porous medium. We present a study of the nonlinear Poisson–Boltzmann equation in a random medium, establish convergence of the stochastic homogenization procedure and prove well-posedness of the two-scale homogenized equations. In addition, after separating scales, we prove that the effective tensor satisfies the so-called Onsager properties, that is the tensor is symmetric and positive definite. This result shows that the Onsager theory applies to random porous media. The strong convergence of the fluxes is also established. In the periodic case homogenization results for the mentioned system have been obtained in Allaire et al (2010 J. Math. Phys. 51 123103).

Stepwise induced passivation film formation on the surface of spherical hard carbons enabling ultra-stable potassium ions storage

Potassium-ion storage devices are seen as a form of prospective substitute for large-scale electrochemical energy storage because of the low cost and the fast charge transport in electrolytes. However, the rosy scenario is compromised by developing ultra-stable electrode materials to ensure long-term cycling performance. Herein, with sucrose as the carbon source, we construct two carbon materials, namely hard carbon spherules (HCS) and active hard carbons (AHCS), as anode and cathode materials, respectively, to fabricate high-performance potassium-ion hybrid capacitors (PIHC). Benefiting from the advantageous ionic conductivity and the comparatively stable passivation film, HCS bonding with sodium alginate delivers superior rate performance and high pseudocapacitive proportion. In situ electrochemical impedance spectroscopy and distribution of relaxation time analysis combined with ex situ scanning electron microscope images reveal that the formation of solid electrolyte interface on the surface of the HCS during the initial discharge can be explained as a gradually forming process. As expected, the HCS//AHCS PIHC device delivers a high energy density of 116 Wh kg−1 at a power density of 218 W kg−1 and exhibits an ultra-stable lifespan over 20000 cycles. This study provides a worthy reference for the value-added utilization of biomass in innovative potassium-based energy storage technology.

Probing the Origin of Viscosity of Liquid Electrolytes for Lithium Batteries

AbstractViscosity is an extremely important property for ion transport and wettability of electrolytes. Easy access to viscosity values and a deep understanding of this property remain challenging yet critical to evaluating the electrolyte performance and tailoring electrolyte recipes with targeted properties. We proposed a screened overlapping method to efficiently compute the viscosity of lithium battery electrolytes by molecular dynamics simulations. The origin of electrolyte viscosity was further comprehensively probed. The viscosity of solvents exhibits a positive correlation with the binding energy between molecules, indicating viscosity is directly correlated to intermolecular interactions. Salts in electrolytes enlarge the viscosity significantly with increasing concentrations while diluents serve as the viscosity reducer, which is attributed to the varied binding strength from cation–anion and cation–solvent associations. This work develops an accurate and efficient method for computing the electrolyte viscosity and affords deep insight into viscosity at the molecular level, which exhibits the huge potential to accelerate advanced electrolyte design for next‐generation rechargeable batteries.

Probing the Origin of Viscosity of Liquid Electrolytes for Lithium Batteries.

Viscosity is an extremely important property for ion transport and wettability of electrolytes. Easy access to viscosity values and a deep understanding of this property remain challenging yet critical to evaluating the electrolyte performance and tailoring electrolyte recipes with targeted properties. We proposed a screened overlapping method to efficiently compute the viscosity of lithium battery electrolytes by molecular dynamics simulations. The origin of electrolyte viscosity was further comprehensively probed. The viscosity of solvents exhibits a positive correlation with the binding energy between molecules, indicating viscosity is directly correlated to intermolecular interactions. Salts in electrolytes enlarge the viscosity significantly with increasing concentrations while diluents serve as the viscosity reducer, which is attributed to the varied binding strength from cation-anion and cation-solvent associations. This work develops an accurate and efficient method for computing the electrolyte viscosity and affords deep insight into viscosity at the molecular level, which exhibits the huge potential to accelerate advanced electrolyte design for next-generation rechargeable batteries.

Disentangling the Li-Ion transport and Boundary Phase Transition Processes in Li10 GeP2 S12 Electrolyte by In-Operando High-Pressure and High-Resolution NMR Spectroscopy.

Li-ion transport and phase transition of solid electrolytes are critical and fundamental issues governing the rate and cycling performances of solid-state batteries. In this work, in-operando high-pressure nuclear magnetic resonance (NMR) spectroscopy for the solid-state battery is developed and applied, in combination with 6 Li-tracer NMR and high-resolution NMR spectroscopy, to investigate the Li10 GeP2 S12 electrolyte under true-to-life operation conditions. The results reveal that the Li10 GeP2 S12 phase may become more disordered and a large amount of conductive metastable β-Li3 PS4 as the glassy matrix in the electrolyte transforms into less conductive phases, mainly γ-Li3 PS4 , when high current densities (e.g., ≥0.5mA cm-2 ) are applied to the electrolyte. The overall Li-transport also varies and shows a tendency of boundary phases and Li10 GeP2 S12 synergistic dominant conduction at high currents. Accordingly, a mechanism of structural change induced by stress variation due to the drastic morphological change during Li-In alloying at high currents, and the local Li+ diffusion coefficient discrepancy is proposed. These new findings of Li-ion transport and boundary phase transition in Li10 GeP2 S12 solid electrolyte under high-pressure and high current density are first reported and will help provide previously lacking insights into the relationship of structure and performance of Li10 GeP2 S12 .

Use of Fe-H3BTC and GO Compounds To Prepare N/Fe-Doped Carbon for a High-Performance Oxygen Reduction Reaction Catalyst.

Zinc-air batteries (ZABs), as a new type of energy storage and conversion device, have received lots of attention due to their high energy density and low cost. The electrode material is a key factor for improving the performance of ZABs. Here, a facile strategy for the fabrication of N-rich porous carbon is reported. H3BTC and GO are selected as carbon precursors, histidine and Fe(NO3)3 are used as ligands, and urea is used as a N source and template. After the conventional drying of the complex and following carbonization process, serial N-doped carbon materials are prepared. The composition and structure of the material are characterized, and the effect of the ligand is studied. The hierarchical porous structure facilitates the full exposition of N and trace of Fe active sites and benefits the transportation of electrolytes, thus improving the oxygen reduction reaction (ORR). The ORR performances show that the porous carbon has a positive initial and half-wave potential, good limiting current density, a near four-electron transfer process, and better methanol resistance and durability. The assembled ZAB exhibits high specific capacity (880.4 mAh gZn-1), excellent open-circuit voltage (1.54 V), and superior cycling stability, which further provides the significant potential for its application.

Improved Structural Stability of Charged Hydrogels under Organic CO2 Reduction Products: Effect of Acrylate and Methacrylate Backbone Linkages

Understanding the mixed solute transport behavior of CO2 reduction products (methanol and formate) in ion exchange membranes (IEMs) is of interest for CO2 reduction cells (CO2RCs). The role of an IEM in a typical CO2RC is to suppress the crossover of all CO2 reduction products while allowing the transport of electrolytes. Tuning the polymer rigidity of the membrane is a key contributor to such highly controlled transport of organic solutes in a dense hydrated membrane. Here, we investigate the mixed solute transport behavior of methanol and formate in a series of tough phenyl acrylate-based cross-linked IEMs. We then investigate the effects of a structural modification on mixed solute transport behavior by introducing quaternary carbons within the membrane. We measured the relative permittivity properties of swollen films to determine if the water hydrogen bonding environment within the IEMs, which is related to maintaining selective ion transport within the membrane (electrolytes over CO2 reduction products), was impacted by various organic solutes. We observed films with methacrylate backbone linkages have effectively constant relative permittivities when exposed to solutions containing methanol, formate, and a mix thereof. These findings may assist in designing membranes for applications, including CO2 reduction cells and water–organic separation.

Improved ion conductivity and interface characteristics of the Te-doped solid NASICON electrolyte Li1.5Al0.5Ge1.5(PO4)3 with graphite coating

Solid Te-doped Li1.5Al0.5TexGe1.5-x(PO4)3 (LATGP) electrolyte materials are successfully prepared by the sol-gel method. The structure, morphology, and ionic and electronic conductivities of samples with different doping concentrations are analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and DC polarization. The results reveal that Te doping can effectively promote the ionic conductivity of LAGP material, reaching a value of 6.33 × 10−4 S cm−1 at room temperature for Li1.5Al0.5Te0.06Ge1.44(PO4)3. Then, LATGP sheets are coated with graphite (G) by the magnetron sputtering method to improve the interfacial characteristics between the Li metal and LAGP electrolyte at high current densities. The polarization voltage curves of the symmetric graphite-modified Li/G@LATGP@G/Li cells remain stable after 800 h at high current densities of 0.5 mA cm−2 and 1 mA cm−2. The solid-state Li/G@LATGP/LiFePO4 full cell presents an initial specific discharge capacity of 154.4 mAh·g−1 at a current density of 0.1 mA cm−2 as well as a capacity retention of 87.8% after 100 cycles. These results indicate that Te doping combined with graphite surface coating can effectively improve the ion transport and interfacial characteristics of solid LAGP electrolyte.

Binary metal oxide (MnO2/SnO2) nanostructures supported triazine framework-derived nitrogen-doped carbon composite for symmetric supercapacitor

A high-performance supercapacitor was fabricated using binary metal oxide (manganese oxide and tin oxide) decorated triazine framework-derived nitrogen-doped carbon (MnO2@SnO2/T-NC) composites. Morphological analysis showed that the SnO2/T-NC composite surface was densely decorated with MnO2 nanorods (<20 nm). The MnO2@SnO2/T-NC (5:1) composite delivered a capacitance of 676 F g−1 at 1 A g−1current density. The symmetric system displayed a capacitance of 91.1 F g−1 at 1 A g−1 with good cycling stability. After 7000 cycles, the device withheld 92.3 % of its total capacitance at 3 A g−1. The electrode's high performance may be ascribed to the redox reaction of metal oxides and fast electrolyte transport through porous carbon. After charging the symmetric supercapacitor device for 23 s at 4.4 V, green (2.0 V) and blue (3.3 V) light-emitting diodes were powered for 21 and 10 min, respectively.

Theoretical Design of Defects as a Driving Force for Ion Transport in Li3OBr Solid Electrolyte

Due to ever‐increasing concerns about safety issues in using Li ionic batteries, solid electrolytes have extensively explored. The Li‐rich anti‐perovskite Li3OBr has been considered as a promising solid electrolyte candidate, but it still suffers challenges to achieve a high ionic conductivity owing to the high intrinsic symmetry of the crystal lattice. Herein, we presented a design strategy that introduces various point defects and grain boundaries to break the high lattice symmetry of Li3OBr crystal, and their effect and microscopic mechanism of promoting the migration of Li‐ion were explored theoretically. It has been found that are the dominant defects responsible for the fast Li‐ion diffusion in bulk Li3OBr and its surface, but they are easily trapped by the grain boundaries, leading to the annihilating of the Frenkel defect pair and thus limits the diffusion at the grain boundaries. The defect near the grain boundaries can effectively drive across the grain boundary, thereby converting the carrier of Li+ migration from in the bulk and surface to at the grain boundary, and thus improving the ionic conductivity in the whole Li3OBr crystal. This work provides a comprehensive insight into the Li+ transport and conduction mechanism in the Li3OBr electrolyte. It opens a new way of improving the conductivity for all‐solid‐state Li electrolyte material through the defect design.