Efficient Ion Transport Research Articles

Hydrophilic flexible di-piperidine crosslinked membranes with highly effective ionic channels for water electrolysis

The combination of cationic side chains and hydrophilic oxygenated cross-linkers facilitates the construction of efficient and continuous ion transport channels, improving ionic conductivity and enhancing the water electrolysis performance of AEMs.

Aromatic foldamer-derived transmembrane transporters.

This review is the first to focus on transmembrane transporters derived from aromatic foldamers, with most studies reported over the past decade. These foldamers have made significant strides in mimicking the essential functions of natural ion channel proteins. With their aromatic backbones rigidified by intramolecular hydrogen bonds or differential repulsive forces, this innovative family of molecules stands out for its structural diversity and functional adaptability. They achieve efficient and selective ion and molecule transport across lipid bilayers via carefully designed helical structures and tunable large cavities. Recent developments in this field highlight the transformative potential of foldamers in therapeutic applications and biomaterial engineering. Key advances include innovative molecular engineering strategies that enable highly selective ion transport by fine-tuning structural and functional attributes. Specific modifications to macrocyclic or helical foldamer structures have allowed precise control over ion selectivity and transport efficiency, with notable selectivity for K+, Li+, H+ and water molecules. Although challenges remain, future directions may focus on more innovative molecular designs, optimizing synthetic methods, improving membrane transport properties, integrating responsive designs that adapt to environmental stimuli, and fostering interdisciplinary collaborations. By emphasizing the pivotal role of aromatic foldamers in modern chemistry, this review aims to inspire further development, offering new molecular toolboxes and strategies to address technological and biological challenges in chemistry, biology, medicine, and materials science.

Efficient photo-driven ion pump through slightly reduced vertical graphene oxide membranes.

Solar energy can be harvested using biological light-driven ion pumps for the sustainability of life. It remains a significant challenge to develop high-performance artificial light-driven ion pumps for solar energy harvesting in all solid-state materials. Here, we exploit the benefits of short channel lengths and efficient light absorption to demonstrate efficient photo-driven ion transport in slightly reduced vertical graphene oxide membranes (GOMs). Remarkably, this photo-driven ion pump exhibits excellent ability, countering a 10-fold electrolyte concentration gradient. We propose a plausible mechanism where light illumination enhances the electric potential of ion channels on GOMs triggered by the separation of photoexcited charge carriers between the sp2 and sp3 carbon clusters. This results in the establishment of an electric potential difference across the effective ion channels composed of sp3 carbon clusters, thus driving the directional transport of cations from the illuminated side to the non-illuminated side. The promising results of this study provide new possibilities for the application of vertical 2D nanofluidic membranes in areas such as artificial photosynthesis, light harvesting, and water treatment.

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.

Enhanced ion transport in ultrathin regenerated cellulose supercapacitor separators

This work reports the fabrication of regenerated cellulose-based separators with efficient ion transport properties, high porosity, and excellent electrolyte wettability using vacuum freeze-dried cellulose membranes.

Electrospinning-assisted porous skeleton electrolytes for semi-solid Li-O2 batteries.

Solid-state lithium-oxygen batteries offer great promise in meeting the practical demand for high-energy-density and safe energy storage. We have developed fibrous gel polymer electrolytes (GPEs) using a polyacrylonitrile (PAN) matrix via electrospinning. The 3D structure of GPEs enhances electrolyte absorption, while the interconnected design promotes strong interactions between Li+ and polar groups within the PAN matrix, thereby improving ion transport efficiency. In practical tests, both lithium symmetric cells and Li-O2 batteries demonstrated the ability to operate at high current densities over long cycles.

Enhanced stability and the lithium storage mechanism of oxygen vacancy-induced heterogeneous Li4Ti5O12/TiO2(B) anolytes

The Li4Ti5O12/TiO2(B) heterostructure, enriched with oxygen vacancies, significantly improves the stability of the slurry electrode while augmenting lithium ion transport efficiency.

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 102.4mAhg-1, with 84.4% capacity retention after undergoing 3448 cycles over a duration of 270days. 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.

(Invited) Functional Protective Coatings Based on Polysaccharides and Single-Ion Conducting Polymers for Li Metal Batteries

Li metal batteries are regarded as a promising system to overcome the energy density limitations of the current graphite anode Li-ion batteries, by taking advantage of the low reduction potential of lithium metal (-3.04 V vs SHE) and extremely high theoretical capacity (3860 mAh g-1). However, its use is still plagued with challenges that must be solved in order to achieve a successful Li-metal battery operation, that primarily relies on the performance, stability, and reversibility of the anodic side. Those challenges are related to safety concerns, mainly caused by the uncontrolled growth of high surface area lithium (HSAL) and high volumetric expansion. In this sense, to enable the safe use of Li metal, the concept of protective coating has been proposed, enabling to tailor of adequate interphases that can thermodynamically stabilize the lithium metal surface, and therefore improve the lifespan and safety of the battery. The ideal coating should possess a balance between mechanical strength, flexibility, and ionic conductivity, at the time it enables a uniform and efficient transport of lithium ions. Additionally, it must be electronically insulating and possess high chemical and electrochemically stability. In this context, polymeric coatings can offer good flexibility and elasticity which makes them suitable to adapt to the volumetric changes during lithium stripping/deposition cycles. Moreover, they can form uniform films, creating an ideal contact with lithium metal surface. An attractive group of materials that can provide numerous advantages such as high chemical, mechanical and thermal stability, are polysaccharides, aside from being the highly abundant and renewable resource on the Earth, which can be obtained in different forms.Several studies have shown that concentration polarization during battery operation is the main responsible for HSAL generation and limited cycle life, due to the coupled anion-cation movement in the electrolyte. To solve this problem the use of single-ion conducting polymers (SICPs) can result beneficial due to their immobilized anions to a polymeric backbone, which eases lithium ion transport, boosting lithium transference number (𝑡𝐿𝑖+). In addition, the selection of an appropriate polymeric backbone that can withstand volumetric changes, and allow a satisfactory ionic conductivity is essential. In this regard, the use of cellulose is preferred due to their film formation and mechanical properties, lightweight, high abundance, and biodegradability. Herein, a polymeric coating based on cellulose and P(LiMTFSI) single-ion conductor polymer is studied as a protective coating for metallic Li, in order to prevent HSAL initiation and propagation, as well as to enhance electrochemical stability in liquid and solid polymer electrolyte. The coating effectiveness is tested by casting the solution on activated lithium surface and performing lithium stripping/deposition in Li/Cu pouch cells. Additionally, the correlation with its electrochemical and physicochemical properties is performance based on microscopy and spectroscopy technics, to study the most relevant parameters influencing Coulombic Efficiency.

Developing efficient, binder-free 3D porous Ti3C2Tx-MXene electrodes for enhanced capacitive deionization towards desalination

Research and design of high-performance Faraday electrode have always been a key to enhance the desalination performance of membrane capacitive deionization. This study developed a binder-free 3D porous Ti3C2Tx-MXene electrode by depositing Ti3C2Tx-MXene nanosheets uniformly onto the graphite electrodes through electrophoretic deposition, followed by a straightforward liquid‑nitrogen freezing and vacuum drying. Uniform-interconnected and conductive network structure of the electrode provided abundant active sites and promoted efficient ion diffusion and transport rate. High pseudocapacitance (287 F/g) and large surface area (16.4 m2 g−1) of the 3D porous electrode led to excellent desalination performance (59 mg g−1) and rapid desalination rate (0.55 mg g−1 s−1), substantially outperforming the conventional coated electrodes. This research provided technical support for the rapid development of capacitive deionization technology towards high-efficient desalination.

In Situ Gelled Covalent Organic Frameworks Electrolyte with Long-Range Interconnected Skeletons for Superior Ionic Conductivity.

Covalent organic frameworks (COFs) present an ideal platform for ion transport owing to their tunable and ordered nanochannels at the single-digit scale. However, achieving superior COF-based electrolytes remains challenging because of the mismatch between the intricate synthesis processes of COFs and the battery preparation environment, which makes it difficult to build continuous ion channels and low-impedance electrochemical interfaces for devices. Here, we present an in situ gelation method to produce COF gel electrolytes (CGEs) within liquid carbonate electrolyte, integrating COF synthesis with their applicability in batteries. This method leads to long-range interconnected and highly crystalline skeletons of COFs from a robust precoordination structure between lithium salts of liquid electrolyte and building blocks. By incorporating the lithium affinity groups in the COFs, the developed CGEs show a remarkable 3-fold enhancement in ionic conductivity, reaching up to 10.5 mS cm-1 compared to the corresponding liquid carbonate electrolytes. Furthermore, the CGEs exhibit a low activation energy of 0.068 eV, ensuring efficient ion transport, while demonstrating dendrite-free lithium deposition even after prolonged testing periods exceeding 1800 h. These CGEs exhibit excellent rate performance (reversible capacity up to 101 mAh g-1 at a current density of 3C, 1C = 170 mAh g-1) in Li-LiFePO4 coin cells and reversible cycling under extreme conditions (reversible capacity up to 158 mAh g-1 under folding state at 0.1C) in pouch cells. Importantly, our novel methodology extends beyond lithium-ion systems, as it can also be applied to the synthesis of CGEs utilizing potassium, magnesium, zinc, sodium, and calcium ions.

Enhanced Ion Transport Through Mesopores Engineered with Additional Adsorption of Layered Double Hydroxides Array in Alkaline Flow Batteries.

Efficient mass transfer in electrodes is essential for the electrochemical processes of battery charge and discharge, especially at high rates and capacities. This study introduces a 3D electrode design featuring layered double hydroxides (LDHs) nanosheets array grown in situ on a carbon felt surface for flow batteries. The mesoporous structure and surface characteristic of LDH nanosheets, especially, the hydroxyl groups forming a unique "H-bonding-like" geometry with ferrous cyanide ions, facilitate efficient adsorption and ion transport. Thus, the designed LDHs electrode enables the alkaline zinc-iron flow battery to maintain a voltage efficiency of 81.6% at an ultra-high current density of 320mA cm-2, surpassing the values reported in previous studies. The energy efficiency remains above 84% after 375 cycles at a current density of 240mA cm-2. Molecular dynamics simulations verify the enhanced adsorption effect of LDH materials on active ions, thus facilitating ion transport in the battery. This study provides a novel approach to improve mass transport in electrodes for alkaline flow batteries and other energy storage devices.

Solvent-Tailored Reversible Self-Assembly: Unveiling Ionic Transport Nanochannels in Block Copolymer Composite Electrolytes.

Block copolymer composite electrolytes have gained extensive attention for their promising performance in ionic conductivity and mechanical properties, making them valuable for future technologies. The control of the ionic conductivity through the self-assembly of block copolymers, however, remains a great challenge, especially in confined environments. In this study, we prepare block copolymer composite electrolytes using polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) as the polymer matrix and anodic aluminum oxide (AAO) templates as the ceramic skeleton. The self-assembly of SEO creates nanoscale ion transport pathways in the PEO regions through ionic interactions with lithium salts. The nanopores of the AAO templates provide a confined environment for complex phase separation of SEO controlled by selective solvent vapor annealing. Our findings demonstrate that transforming self-assembled SEO structures allows for precise control of ion transport pathways with cylindrical structures exhibiting 20 times higher ionic conductivities than those of helical structures. For AAO templates with pore diameters of 20 nm (SEO-LiTFSI@AAO-20), the ionic conductivities are approximately 410 times higher than those with pore diameters of 200 nm (SEO-LiTFSI@AAO-200), owing to the larger specific surface areas within the smaller nanopores. Utilizing the self-assembly of SEO not only enables the construction of vertically aligned ion transport channels on various scales but also offers a fascinating approach to tailor the conductive capabilities of composite electrolytes, enhancing the ion transport efficiency and allowing for the flexible design of block copolymer composite electrolytes.

SOx Functionalized NiOOH Nanosheets Embedded in Ni(OH)2 Microarray for High-Efficiency Seawater Oxidation.

A nano-micro heterostructure has been established to address the challenges of selectivity, stress, pitting corrosion, and long-term durability of anodes in unpurified seawater. The heterostructure comprisedNiOOH nanosheets embedded within a high surface area Ni(OH)2 microarray, and the surface structure is further functionalized with sulfate (SOx). This cation-selective protective layer impedes chloride (Cl-) diffusion and abstracts H from reaction intermediates, leading to enhanced selectivity and corrosion resistance of the anode. The multilevel porosity within the randomly oriented nanosheets and the underlying support provide short diffusion channels for ions and mass migration, ensuring efficient ion transport and long-term structural and mechanical durability of the active sites, even at high current density. Remarkably, the catalyst requires a small input voltage of 400mV to deliver a current density of 1 Acm-2 and maintains it for over 168 h without noticeable degradation or hypochlorite formation. Spectroscopic analysis and density functional theory (DFT) calculations reveal that the Ni electronic structure in the +3 valence state, its strong structural interaction with the underlying microarray, and the functionality of SOx significantly reduce the required potential for O-O coupling.

A Lithium‐Salt‐Free, Hydrophobic, Solid‐State Poly(Ionic Liquid) Electrolyte Enables Rapid Assembly of Unencapsulated, Removable Electrochromic “Window Tint Film”

AbstractElectrochromic technology that enables modulation of a material's optical properties by application of an applied voltage is utilized in smart windows. However, avoiding water absorption by lithium salt in the electrolyte necessitates complex encapsulated device assemblies that must be constructed under strict atmosphere conditions and are largely unrepairable. Herein, a lithium‐salt‐free, hydrophobic, solid‐state poly(ionic liquid) electrolyte based on strong C─F bonds that exhibits low polarizability, low moisture absorption, and a wide electrochemical window, allowing the fabrication of unencapsulated electrochromic devices with outstanding long‐term cycling and environmental stability are presented. Intimate contact between the electrolyte and the electrode is achieved through integrated in situ polymerization, providing an interface with multiple molecular interactions that impart robust adhesion, efficient ion transport, and excellent stability. To demonstrate the potential of this electrolyte for cost‐effective electrochromic smart windows, low‐cost (≈110 USD m−2), unencapsulated, removable, electrochromic “window tint film” with customizable dimensions and shapes are fabricated.

Construction of anode materials for NiSe-based high energy density lithium-ion capacitors

Nickel selenide has been extensively used in energy storage applications because of its easily adjustable morphology, high theoretical specific capacity, abundant reserves, and low price. It is an idealized anode material for lithium-ion capacitors (LICs). However, the volume effect and ion transport efficiency during the transmission process are low, resulting in improved cycle and rate performance. In view of the above problems, NiSe/carbon nanotube@polyaniline (NiSe/CNT@PANI) nanocomposites are prepared by the hydrothermal method and in-situ polymerization. After 100 cycles at 0.1 A·g−1, the charge specific capacity is 529.3 mAh·g−1. After 300 cycles at 1 A·g−1 and 2 A·g−1, the charge specific capacity is still 271.8 mAh·g−1 and 173.5 mAh·g−1, respectively. Furthermore, the constructed NiSe/CNT@PANI//AC LICs have an initial reversible capacity of 50.9 mAh·g−1 at 0.1 A·g−1, a cycle retention rate of 56.5% after 3000 cycles at 1 A·g−1. When the power density is 199.5 W·kg−1, the energy density is 91.7 Wh·kg−1, and the energy density reaches 53.1 Wh·kg−1 at a high power density of 1995.4 W·kg−1. These results indicate that NiSe/CNT@PANI composites have broad application prospects in LICs.

Design Strategy of High Stability Vertically Aligned RGO@V2O5 Heterostructure Cathodes for Flexible Quasi-Solid-State Aqueous Zinc-Ion Batteries.

Among various cathodes for aqueous zinc-ion batteries (AZIBs), vanadium-based oxides have garnered significant attention in research circles owing to their exceptionally high theoretical specific capacity. However, the outstanding zinc storage capacity of vanadium pentoxide is constrained by its irreversible dissolution in an aqueous solution. Here, we propose a laser reduction of graphene oxide and construct a heterostructure of V2O5 coated with vertically aligned reduced graphene oxide (VrGO). The VrGO nanosheets effectively suppress the dissolution of V2O5 and provide channels for the efficient transport of zinc ions and electrons, so the electrochemical reaction kinetics of the electrode are improved. The AZIB based on the VrGO@V2O5 heterostructure cathode has a high specific capacity of 254.9 mAh g-1 at 0.2 A g-1 and excellent cycle stability with a capacity retention rate of 90.1% after 5000 cycles of charge and discharge. When assembled into a flexible quasi-solid-state AZIB, the capacity of the device is reduced by only 2% after 1000 bending cycles, showing good potential for wearable applications. This work provides a reliable strategy for designing flexible AZIB with high electrochemical performance and structural stability.

A tailored dual-layer electronic shielding interface enables highly stable and dendrite-free solid-state lithium metal batteries

All-solid-state lithium metal batteries (ASSLMBs) have emerged as promising energy storage devices due to their high energy density and enhanced safety features. However, challenges related to Li/electrolyte interface stability and ion transport efficiency hinder the practical implementation of sulfide-based ASSLMBs. In this study, we tailored the Li anode interface from the conventional mosaic structure to dual-layer gradient structure through a simple conversion reaction with an organic fluoride. The dual-layer multifunctional interface consists of a highly flexible and wettable upper layer enriched with organic LiBASF3 compounds and an LiF-rich lower layer with high interfacial energy. Eventually, the glittering integration of targeted surface smoothness, excellent interfacial wettability, and high interfacial energy is verified by experimental and theoretical calculation results. The insulating property of the dual-layer interface can impede electronic tunneling and minimize current leakage into the sulfide solid-state electrolytes. Ultimately, the implementation of interface engineering has shown significant improvements in enhancing the critical current density (CCD, 1.9 mA cm−2) of symmetric batteries, as well as enhancing the long-term cycling stability and capacity retention rate of the FeS2 and LiCoO2 cathodes based full cells.

High entropy oxide coated BaTiO3 enabling high ionic transport

High entropy oxides (HEOs) have gained significant attention for their diverse applications in various fields, including energy-related research. However, their potential in solid oxide fuel cells (SOFCs) remains unexplored. This research presents a practical approach to creating a local gradient field by coating BaTiO3 (BTO) with HEO, enabling efficient and stable ionic transport for fuel cell applications. The coating of 10% HEO on BTO resulted in the HEO@BTO powders demonstrating a maximum power density of 640 mWcm−2 and suitable open circuit voltage (OCV) of 1.085 V at 520 °C. We propose that the local entropy gradient created by the HEO coating on the BTO surface establishes a core-shell structure and facilitates high ion transport through the induced built-in electric field. This work sheds light on the mechanisms underlying the enhanced performance of HEO-coated BTO and offers insights into the design of advanced materials for efficient ionic transport in fuel cell technologies.

High output power moist-electric generator based on synergistic nanoarchitectonics for effective ion regulation

Moisture is ubiquitous in nature and life processes and contains huge amounts of energy. Moist-electric generation is an emerging energy technology that collects energy from the environment and converts it into electrical energy through the interaction of moisture with materials. However, the low power density of moist electric generators (MEG) hinders their further application, and improving the performance of MEG devices remains a challenge. Herein, we propose a synergistic nanoarchitectonics strategy to fabricate MEG by optimizing the paths of the ion generation, transmission and interception processes to obtain excellent power output performance. Highly hydrophilic poly (4-styrensulfonic acid) nano film was used to cover the surface of the porous polyurethane foam framework to form PU@PSS active composite with abundant movable ions, which also aided in water diffusion and provided evaporation channels. Gridded aluminum and PEDOT:PSS nano layer were used as the top electrode and interception layer because of their metallic activities and hydrogen ion adsorption capacities, respectively. Due to its effective water circulation and ion regulation properties, the MEG worked in an all-weather environment and converted energy from air moisture into high-power electrical energy. In addition, the MEG converted ambient heat energy to increase the efficiency of ion transport, thereby increasing the output power. A single MEG spontaneously produced a maximum open-circuit voltage of 1.25 V·cm−2 and a short-circuit current of 150 μA·cm−2 in a heated condition, and provided an ultra-high output power of 1.875 W·m−2 which is an order of magnitude higher than the output power provided by similar MEG devices. Thus, the strategy adopted achieved an ultra-high power output of moist-electric generation, which will inspire the development of next-generation MEG.