Iontronic Devices Research Articles

Multi-Modal Sensing Ionogels with Tunable Mechanical Properties and Environmental Stability for Aquatic and Atmospheric Environments.

Ionogels have garnered significant interest due to their great potential in flexible iontronic devices. However, their limited mechanical tunability and environmental intolerance have posed significant challenges for their integration into next-generation flexible electronics in different scenarios. Herein, the synergistic effect of cation-oxygen coordination interaction and hydrogen bonding is leveraged to construct a 3D supramolecular network, resulting in ionogels with tunable modulus, stretchability, and strength, achieving an unprecedented elongation at break of 10800%. Moreover, the supramolecular network endows the ionogels with extremely high fracture energy, crack insensitivity, and high elasticity. Meanwhile, the high environmental stability and hydrophobic network of the ionogels further shield them from the unfavorable effects of temperature variations and water molecules, enabling them to operate within a broad temperature range and exhibit robust underwater adhesion. Then, the ionogel is assembled into a wearable sensor, demonstrating its great potential in flexible sensing (temperature, pressure, and strain) and underwater signal transmission. This work can inspire the applications of ionogels in multifunctional sensing and wearable fields.

A hydrophobic phase-locking strategy enabling ultrarobust and water-stable self-healing elastomers for underwater ionotronics

Water-resistant conductive elastomers can endow soft electronic devices with reliable sensing performance for motion monitoring and real-time communication in aquatic environments. Nevertheless, traditional conductive elastomers typically suffer from notable shortcomings in terms of inferior mechanical robustness, weak stability, and self-healing capabilities in wet conditions and even underwater, significantly restricting their practical utility. Drawing inspiration from the optimization of multiphase structure, an ultrarobust underwater healable elastomer is constructed by incorporating biomass-derived long-chain segments with a large number of amide/benzene groups into a hierarchical H-bonding supramolecular network. The locking of multiple dynamic bonds by uniformly distributed hard-phase domains with dense hydrophobic barriers leads to the resultant elastomer gaining remarkably enhanced mechanical properties (stretchability, 2217.2 %; toughness, 272.97 MJ m−3) and outstanding capability to autonomously self-heal even underwater with a high ultimate strength over 10 MPa (aqueous healing for 24 h). Notably, it boasts exceptional healing stability to all types of harsh aqueous environments, such as strong acid/alkali, high temperature, and salty water. The application of the developed elastomer is also demonstrated by creating a multifunctional wearable sensor that can accurately detect and transmit information for a variety of human motions in both atmospheric and aquatic environments. The viable strategy reported herein for designing advanced multifunctional healable materials can be applicable for all-environment flexible iontronic devices.

Electrosorption Mechanism of Zwitterionic Amino Acid Neurotransmitters in Iontronic Devices

AbstractNeurotransmitters carrying specific chemical information play a key role in the nervous system, which inspires ion‐based devices to mimic biological functions of nervous system, including sensing, transduction, and computing. In this work, the interaction mechanism of zwitterionic amino acids, glycine (Gly), and gamma‐aminobutyric acid (GABA) (two common inhibitory neurotransmitters) are analyzed with porous carbon electrodes. The charge balance of these zwitterionic neurotransmitters relies on zwitterion protonation in the vicinity of the negative electrodes (produced cations adsorbed by the negative electrode) and deprotonation near the positive electrode (produced anions to balance the positive charges) as demonstrated based on the theoretical dissociation analyses and local pH measurements. Additionally, electrosorption‐induced concentration changes of Gly and GABA in aqueous solutions and phosphate‐buffered saline (PBS) solutions are realized by electrosorption via nanoporous carbon electrodes. Based on this mechanistic understanding, the ionologic functions in printed ionic electrolyte double‐layer transistors are demonstrated. These neurotransmitter‐based iontronic devices hold potential for further organism‐machine interfacing and neuromorphic computing applications.

Stimuli-Responsive Delivery of Ions through Layered Materials-Based Triangular Nanofluidic Device.

The elegance and accuracy of biological ion channels inspire the fabrication of artificial devices with similar properties. Here, we report the fabrication of iontronic devices capable of delivering ions at the nanomolar (nmol) level of accuracy. The triangular nanofluidic device prepared with reconstructed vanadium pentoxide (VO) membranes of thickness 45 ± 5.5 μm can continuously deliver K+, Na+, and Ca2+ ions at the rate of 0.44 ± 0.24, 0.35 ± 0.06, and 0.03 nmol/min, respectively. The ionic flow rate can be further tuned by modulating the membrane thickness and salt concentration at the source reservoir. The triangular VO device can also deliver ions in minuscule doses (∼132 ± 9.7 nmol) by electrothermally heating (33 °C) with a nichrome wire (NW) or applying light of specific intensities. The simplicity of the fabrication process of reconstructed layered material-based nanofluidic devices allows the design of complicated iontronic devices such as the three-terminal-Ni-VO (3T-Ni-VO) devices.

Morphology-Controlled Ion Transport in Mixed-Orientation Polymers.

Advancing iontronics with precisely controlled ion transport is fundamentally important to bridge external organic electronics with the biosystem. This long-standing goal, however, is thus far limited by the trade-off between the active ion electromigration and idle diffusion leakage in the (semi)crystalline film. Here, we presented a mixed-orientation strategy by blending a conjugated polymer, allowing for simultaneously high ion electromigration efficiency and low leakage. Our studies revealed that edge-on aggregation with a significant percolative pathway exhibits much higher ion permeability than that of the face-on counterpart but encounters pronounced leakage diffusion. Through carefully engineering the mixed orientations, the polymer composite demonstrated an ideal switchable ion-transport behavior, achieving a remarkably high electromigration efficiency exceeding one quadrillion ions per milliliter per minute and negligible idle leakage. This proof of concept, validated by drug release in a skin-conformable organic electronic ion pump (OEIP), offers a rational approach for the development of multifunctional iontronic devices.

Enhanced Ionic Power Generation via Light-Driven Active Ion Transport Across 2D Semiconductor Heterostructures.

2D semiconductor heterostructures exhibit broad application prospects. However, regular nanochannels of heterostructures rarely caught the researcher's attention. Herein, a metal-organic framework (i.e., Cu3(HHTP)2) and transition metal dichalcogenides (i.e., MoS2)-based multilayer van der Waals heterostructure (i.e., Cu3(HHTP)2/MoS2) realized band alignment-dominated light-driven ion transport and further light-enhanced ionic energy generation. High-density channels of the heterostructure provide high-speed pathways for ion transmembrane transport. Upon light illumination, a net ionic flow occurs at a symmetric concentration, suggesting a directional cationic transport from Cu3(HHTP)2 to MoS2. This is because Cu3(HHTP)2/MoS2 heterostructures containing type-II band alignment can generate photovoltaic motive force through light-induced efficient charge separation to drive ion transport. After introducing into the ionic power generation system, the maximum power density under illumination can achieve notable improvement under different concentration differences. In addition to the photovoltaic motive force, type-II band alignment and material defect capture-induced surface charge increase also raise ion selectivity and flux, greatly facilitating ionic energy generation. This work demonstrates that 2D semiconductor heterostructures with rational band alignment can not only be a potential platform for optimizing light-enhanced ionic energy harvesting but also provide a new thought for biomimetic iontronic devices.

A Precursor-Derived Ultramicroporous Carbon for Printing Iontronic Logic Gates and Super-Varactors.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor.

Continuous iontronic chemotherapy reduces brain tumor growth in embryonic avian in vivo models

Local and long-lasting administration of potent chemotherapeutics is a promising therapeutic intervention to increase the efficiency of chemotherapy of hard-to-treat tumors such as the most lethal brain tumors, glioblastomas (GBM). However, despite high toxicity for GBM cells, potent chemotherapeutics such as gemcitabine (Gem) cannot be widely implemented as they do not efficiently cross the blood brain barrier (BBB). As an alternative method for continuous administration of Gem, we here operate freestanding iontronic pumps – “GemIPs” – equipped with a custom-synthesized ion exchange membrane (IEM) to treat a GBM tumor in an avian embryonic in vivo system. We compare GemIP treatment effects with a topical metronomic treatment and observe that a remarkable growth inhibition was only achieved with steady dosing via GemIPs. Daily topical drug administration (at the maximum dosage that was not lethal for the embryonic host organism) did not decrease tumor sizes, while both treatment regimes caused S-phase cell cycle arrest and apoptosis. We hypothesize that the pharmacodynamic effects generate different intratumoral drug concentration profiles for each technique, which causes this difference in outcome. We created a digital model of the experiment, which proposes a fast decay in the local drug concentration for the topical daily treatment, but a long-lasting high local concentration of Gem close to the tumor area with GemIPs. Continuous chemotherapy with iontronic devices opens new possibilities in cancer treatment: the long-lasting and highly local dosing of clinically available, potent chemotherapeutics to greatly enhance treatment efficiency without systemic side-effects. Significance statementIontronic pumps (GemIPs) provide continuous and localized administration of the chemotherapeutic gemcitabine (Gem) for treating glioblastoma in vivo. By generating high and constant drug concentrations near the vascularized growing tumor, GemIPs offer an efficient and less harmful alternative to systemic administration. Continuous GemIP dosing resulted in remarkable growth inhibition, superior to daily topical Gem application at higher doses. Our digital modelling shows the advantages of iontronic chemotherapy in overcoming limitations of burst release and transient concentration profiles, and providing precise control over dosing profiles and local distribution. This technology holds promise for future implants, could revolutionize treatment strategies, and offers a new platform for studying the influence of timing and dosing dependencies of already-established drugs in the fight against hard-to-treat tumors.

A Solid-Liquid Bicontinuous Fiber with Strain-Insensitive Ionic Conduction.

Stretchable ionic conductors are crucial for enabling advanced iontronic devices to operate under diverse deformation conditions. However, when employed as interconnects, existing ionic conductors struggle to maintain stable ionic conduction under strain, hindering high-fidelity signal transmission. Here, it is shown that strain-insensitive ionic conduction can be achieved by creating a solid-liquid bicontinuous microstructure. A bicontinuous fiber from polymerization-induced phase separation, which contains a solid elastomer phase interpenetrated by a liquid ion-conducting phase, is fabricated. The spontaneous partitioning of dissolved salts leads to the formation of a robust self-wrinkled interface, fostering the development of highly tortuous ionic channels. Upon stretch, these meandering ionic channels are straightened, effectively enhancing ionic conductivity to counteract the strain effect. Remarkably, the fiber retains highly stable ionic conduction till fracture, with only 7% resistance increase at 200% strain. This approach presents a promising avenue for designing durable ionic cables capable of signal transmission with minimal strain-induced distortion.

Simultaneous Solid Electrolyte Deposition and Cathode Lithiation for Thin Film Batteries and Lithium Iontronic Devices

Simultaneous Solid Electrolyte Deposition and Cathode Lithiation for Thin Film Batteries and Lithium Iontronic Devices

Highly conductive, conformable ionic laser-induced graphene electrodes for flexible iontronic devices

Iontronic devices, recognized for user-friendly soft electronics, establish an electrical double layer (EDL) at the interface between ion gels and electrodes, significantly influencing device performance. Despite extensive research on ion gels and diverse electrode materials, achieving a stable interfacial formation remains a persistent challenge. In this work, we report a solution to address this challenge by employing CO2 irradiation as a bottom-up methodology to directly fabricate highly conductive, conformable laser-induced graphene (LIG) electrodes on a polyimide (PI)-based ion gel. The PI ion gel exhibits exceptional EDL formation at the electrode interface, primarily attributable to efficient ion migration. Particularly, ionic laser-induced graphene (i-LIG) electrodes, derived from the PI ion gel as a precursor, yield high-quality graphene with enhanced crystallinity and an expanded porous structure in the upward direction. This outcome is achieved through a pronounced thermal transfer effect and intercalation phenomenon between graphene layers, facilitated by the presence of ionic liquids (ILs) within the PI ion gel. Ultimately, in comparison to alternative soft electrode-based vertical capacitors, the utilization of i-LIGs and PI ion gels in the vertical capacitor demonstrates reduced interfacial resistance and increased EDL capacitance, emphasizing the extensive potential of iontronic devices. These results not only highlight these features but also introduce a new perspective for advancing next-generation iontronic devices.

Measuring the Capacitance of Carbon in Ionic Liquids: From Graphite to Graphene.

The physical electrochemistry of the carbon/ionic liquids interface underpins the processes occurring in a vast range of applications spanning electrochemical energy storage, iontronic devices, and lubrication. Elucidating the charge storage mechanisms at the carbon/electrolyte interface will lead to a better understanding of the operational principles of such systems. Herein, we probe the charge stored at the electrochemical double layer formed between model carbon systems, ranging from single-layer graphene to graphite and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). The effect of the number of graphene layers on the overall capacitance of the interface is investigated. We demonstrate that in pure EMIM-TFSI and at moderate potential biases, the electronic properties of graphene and graphite govern the overall capacitance of the interface, while the electrolyte contribution to the latter is less significant. In mixtures of EMIM-TFSI with solvents of varying relative permittivity, the complex interplay between electrolyte ions and solvent molecules is shown to influence the charge stored at the interface, which under certain conditions overcomes the effects of relative permittivity. This work provides additional experimental insights into the continuously advancing topic of electrochemical double-layer structure at the interface between room temperature ionic liquids and carbon materials.

Manual shaking exfoliation of large‐size two‐dimensional LiInP2S6 nanosheets with exponential change in ionic conductivity for water detection

AbstractLarge‐sized and atomically thin two‐dimensional metal thiophosphate materials have been widely exploited in detectors due to their rich physical/chemical properties of high surface area and massive adjustable sites. However, existing production methods are limited in terms of meeting the demanding challenges in achieving the scalable fabrication of high‐quality nanomaterials under mild conditions. Here, we develop a facile intercalation–exfoliation method that can fabricate large lateral size (&gt;23 μm) and few‐layer LiInP2S6 nanosheets with high crystalline quality fast. Due to the advantage of hydrophilicity of lithium, swelled interlayer spacing can be obtained, which enables the rapid exfoliation by only slight manual shaking within tens of seconds. Concomitantly, the inorganic LiInP2S6 film manufactured by nanosheets has inter‐connected ionic channels, which can be adjusted on the basis of the water content, enabling tunable ionic conductivity. As a result, ionic conductor films using ions as charge carriers can achieve high water response with good repeatability and excellent long‐term stability in a wide moisture range. Moreover, the as‐prepared detector has excellent capability in real‐time noncontact human–machine interfacing. This study, not only is a powerful strategy for the fabrication of large‐sized and high‐quality nanosheets presented but also proof for the promising development of iontronic devices in new applications.

Ion current oscillation of polyelectrolyte modified micropipettes.

Here, we report for the first time that ion current oscillation (ICO) with periodic amplitude and frequency can autonomously occur at polyimidazole brush (PvimB) modified pipettes in an asymmetric solution with a pH gradient (e.g. pH 6.0/pH 8.0). Experimental results demonstrated that under a strong bias voltage, the proton responsive PvimB-modified pipettes exhibited significant current switching behavior under negative bias voltages, which contributed to the periodic oscillating ion current under constant biases. Based on this dynamic, the frequency and amplitude of the ICO phenomenon were regulated by adjusting the pH gradient in the asymmetric solution. ICOs under different bias voltages were further explored to show the voltage-dependent nature of this phenomenon. This observation of ICO phenomena offers a new strategy for designing iontronic devices with dynamic conductivity changes induced by surface chemical interactions within spatial confinements.

Pom Functionalized Ionogels with Tunable Optical, Mechanical, Electrical, and Sensory Properties

AbstractIonogels, with wide applications in tissue engineering, soft robotics, and flexible iontronic devices, require tunable optical, mechanical, and electrical properties for advanced functionality applications. Here, a facile strategy is reported to tune a set of properties of ionogels via tuning the redox states of the added polyoxometalate (POM) clusters. Upon external electrical stimuli, the POM clusters in the ionogels can be reversibly tuned from a transparent, oxidized state to a blue, reduced state. The redox states of the POM anions influence the POM‐polymer interactions, which promotes the in situ modulation of the ionogel properties reversibly over a large window: optical transparency from 91% to 7%, dissipated energy from 0.9 to 3.1 MJ m−3, elastic modulus from 1.5 to 2 MPa, conductivity from 1.6 × 10−4 to 2.2 × 10−4 S cm−1. Meanwhile, the sensory properties of the ionogels can be modulated simultaneously. For strain sensing and pressure sensing, the GF can be tuned from 2.3 to 7.2, and the sensitivity can be tuned from 0.8 to 1.2 kPa−1. Such an ionogel with tunable optical, mechanical, and electrical properties may find a variety of applications meeting specific demands. The POM functionalization strategy may also bring new insights into the design of the stimuli‐responsive ionogels.

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3.

Ion injection controlled by an electric field is a powerful method to manipulate the diverse physical and chemical properties of metal oxides. However, the dynamic control of ion concentrations and their correlations with lattices in perovskite systems have not been fully understood. In this study, we systematically demonstrate the electric-field-controlled protonation of La2/3Sr1/3MnO3 (LSMO) films. The rapid and room-temperature protonation induces a colossal lattice expansion of 9.35% in tensile-strained LSMO, which is crucial for tailoring material properties and enabling a wide range of applications in advanced electronics, energy storage, and sensing technologies. This large expansion in the lattice is attributed to the higher degree of proton diffusion, resulting in a significant elongation in the Mn-O bond and octahedral tilting, which is supported by results from density functional theory calculations. Interestingly, such a colossal expansion is not observed in LSMO under compressive strain, indicating the close dependence of ion-electron-lattice coupling on strain states. These efficient modulations of the lattice and magnetoelectric functionalities of LSMO via proton diffusion offer a promising avenue for developing multifunctional iontronic devices.

Unveiling the Synergy of Polymer–Salt Compositions for Properties Enhancement of Solid Polymer Electrolytes Based on PEO/PVP Blend Polymer Matrix and LiTFSI Dopant Salt

Solid polymer electrolytes (SPEs) are ion-dipole complexes credited to their use in the design and development of widespread solid-state ion conducting innovative devices. Accordingly, herein, two sets of highly flexible, stretchable, and sticky type SPE films based on poly(ethylene oxide) (PEO)/ poly(vinyl pyrrolidone) (PVP) blend as host matrix of different compositional ratios (i.e., 25/75, 50/50, and 75/25 wt/wt%) with 30 and 50 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as ionic dopant salt, and also one sample of polymer-in-salt (PiS) comprised the 50/50 wt/wt% polymer blend matrix and 60 wt% salt, are prepared and characterized in detail. These SPEs are predominantly amorphous having substantial absorbance for ultraviolet-visible radiations and tunable wide range energy band gaps. The 20 Hz—1 GHz broadband dielectric permittivity, loss angle tangent, and electrical conductivity spectra explained a variety of polarization and structural relaxation processes and the mechanism of ion transport ruled by the compositional synergy of polymer and salt in these SPEs. The highest ionic conductivity with appreciable electrochemical performance of the SPE is found for the PEO-rich blend matrix with 50 wt% of LiTFSI dopant. We conclude the suitability of these enhanced promising propertiesSPEs for the development of futuristic ion-conducting energy storage as well as revolutionary iontronic devices.

The role of impurities in porous carbons for bioinspired iontronic devices

Ion-controlled electronics use biocompatible electrolytes to realize multiple functions, such as ionic resistors, ionic diodes, and ionic transistors, endowing them with huge biologic application potentials, ranging from sensing to information processing. Biocompatible porous carbons with exceptionally high surface areas enable high capacitance for biologic ions electric-double-layer capacitive devices. However, we find an unexpectedly high content of water-soluble ionic impurities in commercial and custom designed carbons, which affects the capacitive behavior of carbons in the pure water electrolyte and thereby affects the precise control of ions transport induced by electric polarization of porous carbon electrodes. Complementary analytical techniques are used to analyze the commercial clean activated carbon ColorSorb (AC-CS) illuminating the influence of adsorbed ionic impurities for the electrosorption mechanism in a low concentrated bioactive choline chloride (ChCl) electrolyte. Moreover, the comparison of high purity activated carbon (AC-HP) with pure AC-CS suggests the roles of ionic impurities for the capacitive behavior in ChCl and pure water electrolytes. Our work encourages to reconsider the importance of adsorbed ionic impurities for the carbon’s property and application in capacitive devices, and clarifies the influence of ionic impurity release from porous carbon for ion depletion and release processes.

Emerging Iontronic Neural Devices for Neuromorphic Sensory Computing.

Living organisms have a very mysterious and powerful sensory computing system based on ion activity. Interestingly, studieson iontronic devices in the past few years have proposed a promising platform for simulating the sensing and computing functions of living organisms, because: 1) iontronic devices can generate, store, and transmit a variety of signals by adjusting the concentration and spatiotemporal distribution of ions, which analogs to how the brain performs intelligent functions by alternating ion flux and polarization; 2) through ionic-electronic coupling, iontronic devices can bridge the biosystem with electronics and offer profound implications for soft electronics; 3) with the diversity of ions, iontronic devices can be designed to recognize specific ions or molecules by customizing the charge selectivity, and the ionic conductivity and capacitance can be adjusted to respond to external stimuli for a variety of sensing schemes, which can be more difficult for electron-based devices. This review provides a comprehensive overview of emerging neuromorphic sensory computing by iontronic devices, highlighting representative concepts of both low-level and high-level sensory computing and introducing important material and device breakthroughs. Moreover, iontronic devices as a means of neuromorphic sensing and computing are discussed regarding the pending challenges and future directions.

A Mechanically Robust, Self‐Healing, and Adhesive Biomimetic Camouflage Ionic Conductor for Aquatic Environments

AbstractFlexible conductive materials capable of simulating transparent ocean organisms have garnered interest in underwater motion monitoring and covert communication applications. However, the creation of underwater flexible conductors that possess mechanical robustness, adhesion, and self‐healing properties remains a challenge. Herein, hydrophobic interaction is combined with electrostatic interaction to obtain a solvent‐free transparent poly(ionic liquid) elastomer (PILE) fabricated using soft acrylate monomers and acrylate ionic liquids. The synergy of hydrophobic and electrostatic interactions can eliminate the hydration of water molecules underwater, giving the PILE adjustable fracture strength, good elasticity, high stretchability, high toughness, fatigue resistance, underwater self‐healing ability, underwater adhesion, and ionic conductivity. As a result, the transparent iontronic sensor generated from the PILE can achieve multifunctional sensing and human motion detection with high sensitivity and stability. In particular, the sensor can also transmit information underwater through stretching, pressing, and non‐contact modes, demonstrating its huge potential in underwater flexible iontronic devices.