Ionic Electrolyte Research Articles

Critical role of submicropores in lignin-based carbon for enhanced supercapacitive performance in aqueous electrolyte

Lignin-based microporous carbon is prepared by KOH activation method. Nitrogen sorption analysis shows that the specific surface area is 1473 m2 g−1 and the micropore size is mainly distributed at 0.65 nm, leading to a capacitance value of 252 F g−1 in H2SO4 electrolyte. To tune the microstructure for better electrochemical performance, cobalt acetate is introduced in the mixture of lignin/KOH. The catalysis of cobalt acetate reduces the heteroatom content of the final porous carbon, resulting in an increased graphitization degree. Moreover, the microporous structure is also tuned by generating more submicropores with pore size of 0.65–0.85 nm. Even though the specific surface area is only 1543 m2 g−1, the submicropore surface area is increased to 1097 from 662 m2 g−1. With the increased graphitization degree and submicropore content, the prepared porous carbon can accommodate more electrolyte ions, contributing to a specific capacitance of 332 F g−1 in H2SO4 electrolyte. This capacitance value is increased by 31.7 % compared with previous carbon without adding cobalt acetate. The assembled supercapacitor cell can deliver a high energy density of 13.4 Wh kg−1. Our findings provide a guide on the microstructure modulation of porous carbon to match aqueous electrolytes with different ionic size.

Immersed boundary method for dynamic simulation of polarizable colloids of arbitrary shape in explicit ion electrolytes.

We develop a computational method for modeling electrostatic interactions of arbitrarily shaped, polarizable objects on colloidal length scales, including colloids/nanoparticles, polymers, and surfactants, dispersed in explicit ion electrolytes and nonionic solvents. Our method computes the nonuniform polarization charge distribution induced in a colloidal particle by both externally applied electric fields and local electric fields arising from other charged objects in the dispersion. This leads to expressions for electrostatic energies, forces, and torques that enable efficient molecular dynamics and Brownian dynamics simulations of colloidal dispersions in electrolytes, which can be harnessed to accurately predict structural and transport properties. We describe an implementation in which colloidal particles are modeled as rigid composites of small spherical beads that tessellate the surface of the particle. The electrostatics calculations are accelerated using a spectrally accurate particle-mesh-Ewald technique implemented on a graphics processing unit and regularized such that the electrostatic calculations are well-defined even for overlapping bodies. We illustrate the effectiveness of this approach with a comprehensive set of calculations: the induced dipole moments and forces for individual, paired, and lattice configurations of spherical colloids in an electric field; the induced dipole moment and torque for anisotropic particles subjected to an electric field; the equilibrium ion distribution in the double layer surrounding charged colloids; the dynamics of charged colloids; and the behavior of ions in the double layer of a polarizable colloid under the influence of an electric field.

Weak solvation effects and molecular-rich layers induced water-poor Helmholtz layers boost highly stable Zn anode

The advancement of aqueous Zn-based energy storage systems encounters major challenges due to the occurrence of side reactions and the growth of dendrites caused by the highly active nature of water in the aqueous electrolyte. Herein, a zwitterion additive named sulfonated amphoteric betaine (referred to as DMAPS) regulates the Zn2+ electrolyte environment through a weak solvation effect to promote highly stable Zn anodes. The inherently occurring anionic (-SO3-) and cationic (-NR4+) counterions in the DMAPS chain can be effectively separated under an external electric field to enable the creation of distinct ion migration pathways, thereby significantly enhancing the transportation of electrolyte ions. Moreover, DMAPS can be adsorbed onto the surface of Zn anode to form a H2O-poor Helmholtz layer, which can serve as a protective barrier to suppress corrosion of the Zn anode by free H2O and inhibits the formation of differential electric field to facilitate the directional deposition of Zn2+. In addition, density functional theory (DFT) and molecular dynamics (MD) further assisted in demonstrating the intrinsic mechanism of the reconstruction of the solvated sheath structure of Zn2+ by DMAPS. As a result, the Zn//Zn symmetric cell in ZnSO4+DMAPS solution can be cycled steadily for 2100 h at a current density of 1 mA cm-2 and 1 mAh cm-2. The assembled Zn ion hybrid capacitor with ZnSO4+DMAPS electrolyte was stably cycled for 20,000 cycles with 90% capacity retention at 5 A g-1.

Electronic Descriptor to Identify the Activity of SACs for E-NRR and Effect of BF3 as Electrolyte Ion.

Electrochemical nitrogen reduction reaction (e-NRR) is an eco-friendly alternative approach to generate ammonia under ambient conditions, with very low power supply. But, developing of an efficient catalyst by suppressing parallel hydrogen evolution reaction as well as avoiding the catalysts poisoning either by hydrogen or electrolyte ion is an open question. So, in order to screen the single atom catalysts (SACs) for the e-NRR, we proposed a descriptor-based approach using density functional theory (DFT) based calculations. We investigated total 24 different SACs of types TM-Pc, TM-N3C1, TM-N2C2, TM-NC3 and TM-N4, considering transition metal (TM). We have considered mainly BF3 ion to understand the role of electrolyte and extended the study for four more electrolyte ions, Cl, ClO4, SO4, OH. Herein, to predict catalytic activity for a given catalyst we have tested 16 different electronic parameters. Out of those, electronic parameter dxz↓ occupancy, identified as electronic descriptor, is showing an excellent linear correlation with catalytic activity (R2=0.86). Furthermore, the selectivity of e-NRR over HER is defined by using an energy parameter ▵G*H-▵G*NNH. Further, the electronic descriptor (dxz↓ occupancy) can be used to predict promising catalysts for e-NRR, thus reducing the efforts on designing future single atom catalysts (SACs).

Optimizing Surface Texture Through Ion Induction for High Areal Capacitance and Enhanced Stability in MXene Electrodes

AbstractTo make supercapacitors a viable commercial product, it is necessary to increase the mass loading (ML) of the electrodes. However, current research on high ML MXene electrodes mainly focuses on internal structure optimization, often neglecting the importance of surface texture in the electrodes, which plays a crucial role in mediating interactions between the internal structure and the electrolyte. This study reports on a simple ion‐intercalation process that can reduce charge transfer resistance and improve cycling stability. Through the integration of 3D visualization models and wide‐angle X‐ray scattering techniques, a comprehensive investigation of the electrode's surface structure and MXene flake arrangement is conducted. The results showed that pre‐oriented aggregates induced by ion‐intercalation create a sophisticated surface structure with rich hills and valleys, promoting electrolyte permeation and ion exchange. This work highlights the significance of surface texture in films and electrodes, guiding the design of high‐performance materials.

Direct Electrolysis of Municipal Reclaimed Water for Efficient Hydrogen Production Using a Bifunctional Non-Noble-Metal Catalyst.

Water electrolysis for green H2 production traditionally requires a stable supply of renewable electricity and pure water. However, spatial separation of renewables and water resources as well as water scarcity per capita in China necessitate unconventional water resources for electrolysis. Reclaimed water produced from municipal wastewater treatment plants is widely distributed with quality improved significantly in recent years, which may be a promising alternative to feedstock. However, there are few reports on the direct use of this wastewater for H2 production. Here, we present a direct electrolysis of reclaimed water for decentralized H2 production by developing a highly efficient and stable bifunctional 3D-dandelion-like (DL) vanadium(V)-doped CoP catalyst grown in situ on Ni foam (NF) in an alkaline electrolyzer. The V-CoP-DL/NF electrode decreases 6.5 and 25% overpotentials of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, compared to noble-metal Pt (HER) and IrO2 (OER) catalysts, and exhibits exceptional durability, as a voltage required for overall reclaimed water splitting only increases by 80 mV (1.81-1.89 V) after 90 days of operation at a current density of 10 mA cm-2. The maximum stable current can reach 1000 mA cm-2. The impacts of potential pollutants in reclaimed water on the performance of electrolysis and the behavior of major wastewater ions in alkaline electrolyte were investigated. The observed exceptional performance is attributed to the catalyst's unique nanostructure, which enhances charge transfer and reactant/electrolyte diffusion. The in situ growth strategy further enhances the conductivity and stability of the catalyst. This work underscores the feasibility of utilizing reclaimed water instead of pure water as the feedstock for sustainable hydrogen production.

Ionic solid-like conductor-assisted polymer electrolytes for solid-state lithium metal batteries

Ionic solid-like conductor-assisted polymer electrolytes for solid-state lithium metal batteries

Highly Stretchable Supercapacitor‐Type Multifunctional Self‐Powered Porous Electronic Skins

AbstractThe development of highly stretchable self‐powered electronic skins with a broad detection range is urgently needed but remains a great challenge. Herein, unprecedented highly stretchable, broad‐range‐response, supercapacitor‐type, one‐body, and self‐powered electronic skins are developed by assembling porous polyurethane/polypyrrole electrode, polyacrylic acid/polyacrylamide ionic gel electrolyte, and porous polyurethane/MXene electrode. The folded porous structure of the electrodes significantly enhances the stretchability, while the modulus‐gradient multilayer structure of the device effectively broadens the pressure detection range. The electronic skins combine self‐powered dynamic/static pressure sensing, ultrabroad detection range (20 Pa–3.5 MPa), ultrahigh stretchability up to 387%, excellent compression stability (5000 cycles under 195 kPa), and good stretching stability (500 cycles under 200% tensile strain). They have the capability of monitoring human body motions, physiological signals, and high pressures from motorcycle tires, as well as tactile sensing of robotic grippers. In addition, they can be applied for highly stretchable thermal management and electromagnetic shielding devices. This work provides a new strategy for the development of highly stretchable, broad‐range‐response, and multifunctional self‐powered wearable electronics and sensors.

Electrochromic Covalent Organic Framework-Assembled Nanofibrous Membranes with Mimetic Chameleon Skin Architectures for Visible and Near-Infrared Camouflage Stealth.

The developments of modern surveillance technology pose great challenges to combat concealment for warfighters. Traditional camouflage suits cannot accommodate the need for camouflage stealth in complex warfare scenarios. Herein, a bidirectional diffusion-controlled in situ synthesis methodology is reported to achieve electrochromic nanofibrous membranes with mimetic chameleon skin structures (CSENs) by assembling electrochromic covalent organic frameworks on nanofibers. CSENs exhibit reversible color changes in the visible and near-infrared ranges under an applied potential with fast response times (25.8 s/26.2 s). The macro- and mesoporous structures in CSENs favored the transportation of electrolyte ions, achieving excellent color difference and coloration efficiency of 35.58 and 1053.26 cm2/C, respectively. Importantly, CSENs feature unique properties of self-standing, breathability, and flexibility, which are attributed to the micrometer pores constructed by entangled nanofibers. As a proof-of-concept study, the CSEN-based flexible electrochromic suit exhibits a dynamic camouflage function in real environments, showing promising properties as smart textiles for dynamic camouflage stealth.

In-depth exploration of the interface mechanism of aqueous ammonium-ion batteries with ionic liquids

Aqueous ammonium-ion batteries have emerged as a research focus in recent years because of their distinctive advantages. Nevertheless, issues such as the side reaction of water, electrode element dissolution and others have an impact on their stability. The experimental findings demonstrate that the system incorporating ionic liquids (ILs) exhibits gratifying electrochemical performance. The Molecular Dynamics (MD) simulation approach was employed to investigate the alterations of NH4Cl aqueous batteries prior to and subsequent to the addition of imidazolium ionic liquids (ILs), with a focus on the impact on the anode's interface. It is found that the addition of ILs can reduce the interfacial water’s content at low charge. Interestingly, in the case of high charge, the water content at the interface didn’t decrease; instead, it increased. This phenomenon is associated with the initial increase followed by a decrease in the number of ionic liquid (IL) cations. Three conformations for IL cations were found near the interface, which are “parallel”, “slant” and “vertical”, and the proportion of the three had a certain influence on the content of interfacial water. The "parallel" configuration is more effective in reducing the interfacial water content, establishing it as the dominant conformation. The findings reported above will offer new theoretical support for the design and modification of aqueous ammonium ion electrolytes.

Electrospun carbon/iron–vanadium oxide nanofibers for high energy density supercapacitors

Highly flexible and conductive carbon nanofibers (CNFs) embedded with pseudocapacitive iron–vanadium oxide (FVO) nanoparticles were fabricated via electrospinning of a metal salt/polyacrylonitrile solution followed by high-temperature annealing (750 °C). CNFs have a graphitic structure with defects, which could accelerate electron mobility and the access of electrolytic ions to the multivalent FVO nanoparticles, respectively. Poly(methyl methacrylate) (PMMA) was introduced as a sacrificial polymer to alter the internal structure of the nanofibers and thus enhance the electrolytic ion transport pathways. Terephthalic acid was added to provide flexibility by increasing the cross-linking within the electrospun fibers. The flexible FVO/CNFs exhibited excellent electrochemical performance. The optimal sample had a high areal capacitance of 1058 mF·cm−2 at a current density of 2.5 mA·cm−2 and showed 100 % capacitance retention during long-term cycling (10,000 cycles). The capacitance at a high current density of 25 mA·cm−2 was 81.3 % of that at a current density of 2.5 mA·cm−2. Using a wider potential window of 0–1.6 V increased the energy density to 389 μW·h·cm−2. The optimal FVO/CNF sample maintained 90 % of its initial capacitance after 200 bending cycles.

Construction of a Borophene-Based Hybrid Aerogel for Multifunctional Applications.

As a novel approach to pursue high-performance multifunctional materials, the structural design of cutting-edge two-dimensional (2D) materials has ignited substantial interests. Borophene, an emerging member in the realm of 2D materials, exhibits crucial attributes, including high theoretical carrier density, electrical conductivity, magnetism, and high aspect ratio, rendering it highly promising for diverse applications. Yet, the exploration of porous structural configurations of borophene remains untapped. Addressing this gap, our study focuses on the fabrication of a multifunctional borophene hybrid foam (CMB-foam). This hybridization leverages the exceptional multifunctionality of MXene alongside borophene within a three-dimensional porous framework, facilitating reflection and absorption of electromagnetic waves, thereby demonstrating remarkable electromagnetic interference (EMI) shielding capabilities. Moreover, this structural configuration exposes an enlarged surface area, thus shortening the transport pathway for electrolyte ions, leading to an excellent energy storage performance. Additionally, CMB-foam performs well in thermal management and thermal insulation. These findings underscore the potential of borophene-based materials in multifunctional applications and offer valuable insights into further performance explorations in this domain.

High-Power Battery Electrodes Fabricated by Acupuncture-Inspired Microneedle Processing.

Advancing battery electrode performance is essential for high-power applications. Traditional fabrication methods for porous electrodes, while effective, often face challenges of complexity, cost, and environmental impact. Inspired by acupuncture, here we introduce an eco-friendly and cost-effective microneedle process for fabricating lithium iron phosphate electrodes. This technique employs commercial cosmetic microneedle molds to create low-curvature holes on electrode surfaces, significantly enhancing electrolyte infiltration and ion transport kinetics. The punctured electrodes were prepared and characterized, with comparisons to pristine electrodes conducted using scanning electron microscopy, 3D metallurgical microscopy, and detailed electrochemical evaluations. Our results show that the microneedle-processed electrodes exhibit superior rate performance and diffusion properties. Simulations and experimental data reveal that the low-curvature holes reduce Li-ion concentration polarization and improve Li-ion transport within the electrode. This enhancement leads to higher specific capacities and better rate capabilities in the punctured electrodes. The findings highlight the potential of this innovative microneedle technique for large-scale production of high-performance electrodes, offering a promising avenue for the development of high-power-density batteries.

Effect of ANSA as an additive on electrodeposited Sn-Ag-Cu alloy coatings in deep eutectic solvent

This study investigates the electrodeposition of Sn-Ag-Cu ternary solder coating in a choline chloride-ethylene glycol DES using 1-amino-2-naphthol-4-sulfonic acid (ANSA) as an additive. The mechanism of ANSA was evaluated through UV–visible absorption spectroscopy, infrared spectroscopy, and CV. The results demonstrate that ANSA, as a multifunctional organic compound, influences the electrodeposition process through its sulfonic acid, amino, and naphthyl groups. When the ANSA concentration is below 600 ppm, its primary action is through an interfacial adsorption mechanism, where lone pairs of electrons on nitrogen and oxygen atoms adsorb onto the electrode surface, and the bulky naphthyl ring inhibits the formation of large deposits. As the ANSA concentration exceeds 600 ppm, complexation becomes the dominant mechanism, competing with the complexation of chloride ions (Cl−) in the choline chloride electrolyte. SEM analysis indicates that as the ANSA concentration increases, the deposited coatings become smoother, denser, and exhibit finer grain sizes. The Scharifker-Hills model was employed to analyze the CA curves before and after the addition of ANSA, revealing that the nucleation mechanism of Sn-Ag-Cu alloy deposition gradually transitions from instantaneous nucleation to progressive nucleation with increasing ANSA concentration.

Enhancing polypropylene-based separator efficiency in lithium-ion batteries through maleic anhydride addition and corona radiation modification

Polypropylene-grafted-maleic anhydride (PPMA) as a modifier of polypropylene (PP) at different contents and the corona radiation for surface ionization at various modification times were applied to promote the PP-based separator efficiency. The determined microstructural characteristics showed an improvement in the separator's porosity of 6–139 % at the tension amounts of 700–900 %, however, more stretching hurts the mechanical properties. The electrostatic interactions formed between the electrolytes and anhydrides increased the electrolyte sorption capacity in the samples and the surface wettability by 740 % and 25 %, respectively. The electrical test results indicated that the anhydrides led to capturing the electrolytes in the separator and created a resistance against the ion diffusion. This phenomenon reduced the separator resistance from 475 to 165 Ω, and enhanced the charge capacity and ion conductivity from 585 to 871 mAh/g and 0.29 to 0.34 S cm−1, respectively, while the PPMA content increased from 20 to 60 wt.%. The achieved FT-IR illustrated that the ionization caused the creation of more polar groups in the LIB separator, which increased the bulk and surface wettability by 420 % and 21 %, respectively, without any change in the microstructure of the separator. However, raising the exposure time in the radiation process decomposed the sample surface and led to damage in the separator microstructure. This issue reduced the separator porosity as well as the electrolyte absorption amount and ion conductivity.

Confined Polyethylene Glycol Anchored in Kaolinite as High Ionic Conductivity Solid-State Electrolyte for Lithium Batteries.

Solid-state electrolytes (SSEs) have garnered significant attention as critical materials for enabling safer, energy-dense, and reversible electrochemical energy storage in batteries. Among the various types of solid electrolytes developed, composite polymer electrolytes (CPEs) have stood out as some of the most promising candidates due to their well-rounded performance. In this study, we choose polyethylene glycol (PEG) as the covalent grafting intercalant and lithium perchlorate as carrier source to prepare a fast lithium ion conductor, K-PEG-Li doped with clay-based active filler as a CPE. The CPE exhibits excellent lithium conduction (4.36 × 10-3 S cm-1 at 25 °C and 3.32 × 10-2 S cm-1 at 115 °C), great mechanical performance with good tensile strength (6.07 MPa) and toughness (strain 313%), and convincing flame-retardancy. These outstanding conducting and mechanical functionalities indicate that such a clay-based active filler doped composite polymer electrolyte will find promising application in solid-state lithium batteries.

Electrochemical analysis of sol-gel and hydrothermal synthesized mesoporous strontium titanate spherical nanoparticles as electrode material for high-performance flexible supercapacitors

Perovskite oxides with large specific surface areas present a promising avenue for enhancing supercapacitor efficiency. This study investigates the remarkable charge storage capabilities of strontium titanate (SrTiO3, STO) synthesized via sol-gel and hydrothermal techniques for electrochemical energy storage applications. The cubic crystal structure of STO, confirmed from X-ray Diffraction analysis, synthesized at lower temperatures through both methods, provides three-dimensional diffusion channels for oxygen anion movement, which is crucial for improving charge storage capacity. X-ray photoelectron spectroscopy confirmed the elements’ oxidation states and their spin-orbit splitting. The spherical nanoparticle morphology was observed in the FESEM images, BET characterization revealed a high specific surface area contributing to more charge storage and mesoporous nature facilitates excellent mass transfer rates of electrolytic ions. Electrochemical measurements and calculations confirmed that sol-gel and hydrothermally synthesized STO electrodes exhibit maximum specific capacitances of 130 F g−1 and 156 F g−1 at 10 mV s−1, respectively. A fabricated flexible supercapacitor device in an aqueous medium maintains a constant voltage of 1.2 V, capable of powering a digital watch. Hence, this study demonstrates the potential of STO electrode-based supercapacitors for a wide range of electrochemical energy storage applications.

An assessment of electroneutrality implementations for accurate electrochemical ion transport models

During the diffusion and migration of ions in electrolytes, the electrodynamic ion-ion interactions prevent charge separation despite different ionic mobilities, ultimately enforcing electroneutrality in the bulk electrolyte. To model ion transport accurately, a method to enforce electroneutrality must be implemented. In this study, four strategies to implement electroneutrality are discussed and evaluated. The ion distributions that result from a transport model with the different electroneutrality implementations are calculated, considering various electrolytes and sets of electrochemical parameters. The meaningfulness and applicability of each implementation are assessed through spatial charge accumulations, transference numbers, and experimental data from the literature. Combining the electrochemical ion transport models with the electroneutrality constraint for all ions is shown to result in an overdetermined system of equations if the driving forces are calculated under neglection of diffusion potentials. The often-reported model simplification of using the electroneutrality constraint to resolve the transport of one specific species explicitly results in non-physically correct mass transport. A practical approach to precisely describe the measured physicochemical ion movements is obtained by equilibrating spatial charges with the ion conduction for every time step in the ion transport model, which is reasonably applicable to multi-ion systems in three-dimensional frameworks. This comprehensive assessment aims to guide readers in selecting an appropriate electroneutrality implementation framework for ion transport models.

Hierarchical porous MXene film with diffusion path optimization for supercapacitor

MXenes have immense potential in electrochemical energy storage owing to their outstanding physicochemical properties such as their oxygen-containing groups that impart additional pseudocapacitance to acidic electrolytes. However, during electrode assembly, MXene nanosheets undergo restacking because of hydrogen bonding and van der Waals forces, which causes electrolyte ions to traverse long diffusion pathways between the long and narrow nanosheets. Exploiting the oxidative properties of Ti3C2Tx, a hierarchical porous MXene film with micro-, meso- and macroporous structures was successfully prepared using a simple hydrothermal oxidation and etching process to create micro- and mesoporous structures, followed by ice templating to prepare three-dimensional (3D) linked macroporous structures. Because these hierarchical pores have synergistic effects on electrochemical activity and electrolyte ion diffusion, the film attained a specific capacitance of 539F/g at a current density of 2 A/g when it was used as a supercapacitor electrode, which corresponds to one of the highest values reported for MXene-based electrodes. The film retained 83% of its specific capacitance when the current density was increased to 40 A/g, and exhibited excellent cycling stability. By using this multi-porous MXene design, synergistic improvement in ion diffusion was successfully realized and thus a new strategy to prepare high-performance supercapacitor electrode materials was developed.

A laboratory-based electrochemical NAP-XPS system for operando electrocatalysis studies

During electrocatalytic reactions, the electrode, adsorbates, electrolyte ions, and solvent molecules at the electrode-electrolyte interface each play an important role. Electrochemical X-ray photoelectron spectroscopy (XPS) holds great promise for deciphering these roles, providing the oxidation state or bonding environment of every element present at the interface. However, combining the vacuum required for XPS with the wet environment needed for electrochemistry constitutes a technical challenge, requiring purpose-built instrumentation and spectro-electrochemical cell design. Here, we present a laboratory-based electrochemical XPS instrument optimized for operando studies on nano-structured electrocatalysts. The core of the system is a 3D printed spectro-electrochemical cell containing a membrane-electrode-graphene assembly. We show that this design enables us to probe the electrode surface, interfacial water, and interfacial ions under well-defined potential control. Meanwhile, the introduction of a mesoporous membrane into the assembly enables the transport of any molecular or ionic reactant towards the working electrode, opening the way to study any aqueous phase electrocatalytic system using laboratory-based electrochemical XPS. We exemplify this for the oxygen reduction reaction.