Search Results (31)

Gel electrolyte-gated organic electrochemical transistors (OECTs) are promising bioelectronic devices known for their high transconductance, low operating voltage, and integration with biological systems. Despite extensive research on the performance of OECTs, a precise model defining the dependence of OECT performance on gel electrolytes is still lacking. In this work, we refine the device model to comprehensively account for the electrical double layer (EDL)’s capacitance of the gel electrolyte. Both experimental data and theoretical calculations indicate that the maximum transconductance of the OECT is contingent upon ion concentration, drain voltage, and scan rate, highlighting a strong correlation between the transconductance and the hydrogel electrolyte. Overall, this model serves as a theoretical tool for improving the performance of OECTs, enabling the further development of bioelectronic devices. Full article

Flexible pressure sensors play an extremely important role in the fields of intelligent medical treatment, humanoid robots, and so on. However, the low sensitivity and the small initial capacitance still limit its application and development. At present, the method of constructing the microstructure of the dielectric layer is commonly used to improve the sensitivity of the sensor, but there are some problems, such as the complex process and inaccurate control of the microstructure. In this work, an ion composite photosensitive resin based on polyurethane acrylate and ionic liquids (ILs) was prepared. The high compatibility of the photosensitive resin and ILs was achieved by adding a chitooligosaccharide (COS) chain extender. The microstructure of the dielectric layer was optimized by digital light processing (DLP) 3D-printing. Due to the introduction of ILs to construct an electric double layer (EDL), the flexible pressure sensor exhibits a high sensitivity of 32.62 kPa⁻¹, which is 12.2 times higher than that without ILs. It also has a wide range of 100 kPa and a fast response time of 51 ms. It has a good pressure response under different pressures and can realize the demonstration application of human health. Full article

Mechanical energy harvesters made from soft and flexible materials can be employed as energy sources for wearable and implantable devices. However, considering how human organs and joints expand and bend in many directions, the energy generated in response to a mechanical stimulus in only one direction limits the applicability of mechanical energy harvesters. Here, we report carbon nanotube (CNT) sheets/an elastomer bilayer harvesting electrode (CBHE) that converts two-axis mechanical stimulation into electrical energy. The novel microwinkled structure of the CBHE successfully demonstrates an electrochemical double-layer (EDL) capacitance change from biaxial mechanical stimulation, thereby generating electrical power (0.11 W kg⁻¹). Additionally, the low modulus (0.16 MPa) and high deformability due to the elastomeric substrate suggest that the CBHE can be applied to the human body. Full article

Electrical double-layer (EDL) synaptic transistors based on organic materials exhibit low thermal and chemical stability and are thus incompatible with complementary metal oxide semiconductor (CMOS) processes involving high-temperature operations. This paper proposes organic–inorganic hybrid synaptic transistors using methyl silsesquioxane (MSQ) as the electrolyte. MSQ, derived from the combination of inorganic silsesquioxanes and the organic methyl (−CH₃) group, exhibits exceptional thermal and chemical stability, thus ensuring compatibility with CMOS processes. We fabricated Al/MSQ electrolyte/Pt capacitors, exhibiting a substantial capacitance of 1.89 µF/cm² at 10 Hz. MSQ-based EDL synaptic transistors demonstrated various synaptic behaviors, such as excitatory post-synaptic current, paired-pulse facilitation, signal pass filtering, and spike-number-dependent plasticity. Additionally, we validated synaptic functions such as information storage and synapse weight adjustment, simulating brain synaptic operations through potentiation and depression. Notably, these synaptic operations demonstrated stability over five continuous operation cycles. Lastly, we trained a multi-layer artificial deep neural network (DNN) using a handwritten Modified National Institute of Standards and Technology image dataset. The DNN achieved an impressive recognition rate of 92.28%. The prepared MSQ-based EDL synaptic transistors, with excellent thermal/chemical stability, synaptic functionality, and compatibility with CMOS processes, harbor tremendous potential as materials for next-generation artificial synapse components. Full article

The primary objective of neuromorphic electronic devices is the implementation of neural networks that replicate the memory and learning functions of biological synapses. To exploit the advantages of electrolyte gate synaptic transistors operating like biological synapses, we engineered electric double-layer transistors (EDLTs) using phosphorus-doped silicate glass (PSG). To investigate the effects of phosphorus on the EDL and synaptic behavior, undoped silicate spin-on-glass-based transistors were fabricated as a control group. Initially, we measured the frequency-dependent capacitance and double-sweep transfer curves for the metal-oxide-semiconductor (MOS) capacitors and MOS field-effect transistors. Subsequently, we analyzed the excitatory post-synaptic currents (EPSCs), including pre-synaptic single spikes, double spikes, and frequency variations. The capacitance and hysteresis window characteristics of the PSG for synaptic operations were verified. To assess the specific synaptic operational characteristics of PSG-EDLTs, we examined EPSCs based on the spike number and established synaptic weights in potentiation and depression (P/D) in relation to pre-synaptic variables. Normalizing the P/D results, we extracted the parameter values for the nonlinearity factor, asymmetric ratio, and dynamic range based on the pre-synaptic variables, revealing the trade-off relationships among them. Finally, based on artificial neural network simulations, we verified the high-recognition rate of PSG-EDLTs for handwritten digits. These results suggest that phosphorus-based EDLTs are beneficial for implementing high-performance artificial synaptic hardware. Full article

Low-voltage Zn-doped CuI thin film transistors (TFTs) gated by chitosan dielectric were fabricated at a low temperature. The Zn-doped CuI TFT exhibited a more superior on/off current ratio than CuI TFT due to the substitution or supplementation of copper vacancies by Zn ions. The Zn-doped CuI films were characterized by scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The Zn-doped CuI TFTs exhibited an on/off current ratio of 1.58 × 10⁴, a subthreshold swing of 70 mV/decade, and a field effect mobility of 0.40 cm²V⁻¹s⁻¹, demonstrating good operational stability. Due to the electric-double-layer (EDL) effect and high specific capacitance (17.3 μF/cm²) of chitosan gate dielectric, Zn-doped CuI TFT operates at a voltage below −2 V. The threshold voltage is −0.2 V. In particular, we have prepared Zn-doped CuI TFTs with two in-plane gates and NOR logic operation is implemented on such TFTs. In addition, using the ion relaxation effect and EDL effect of chitosan film, a simple pain neuron simulation is realized on such a p-type TFTs for the first time through the bottom gate to regulate the carrier transport of the channel. This p-type device has promising applications in low-cost electronic devices, complementary electronic circuit, and biosensors. Full article

Epidermal electronics, an emerging interdisciplinary field, is advancing the development of flexible devices that can seamlessly integrate with the skin. These devices, especially Electric Double Layer (EDL)-based sensors, overcome the limitations of conventional electronic devices, offering high sensitivity, rapid response, and excellent stability. Especially, Electric Double Layer (EDL)-based epidermal sensors show great potential in the application of wearable electronics to detect biological signals due to their high sensitivity, fast response, and excellent stability. The advantages can be attributed to the biocompatibility of the materials, the flexibility of the devices, and the large capacitance due to the EDL effect. Furthermore, we discuss the potential of EDL epidermal electronics as wearable sensors for health monitoring and wound healing. These devices can analyze various biofluids, offering real-time feedback on parameters like pH, temperature, glucose, lactate, and oxygen levels, which aids in accurate diagnosis and effective treatment. Beyond healthcare, we explore the role of EDL epidermal electronics in human-machine interaction, particularly their application in prosthetics and pressure-sensing robots. By mimicking the flexibility and sensitivity of human skin, these devices enhance the functionality and user experience of these systems. This review summarizes the latest advancements in EDL-based epidermal electronic devices, offering a perspective for future research in this rapidly evolving field. Full article

MXene has drawn widespread attention as a potential material for electrode use in capacitive deionization (CDI). However, the applications of MXene are limited by its property of low electrical capacity. Herein, a MnO₂/MXene composite was firstly evaluated in a capacitive deionization system, in which the MnO₂ acts as intercalation-type pseudocapacitive electrodes to enhance the electrical capacity, and MXene provides an electron conduction highway network that improves the charge transfer of the MnO₂. The result showed that the low-crystallinity MnO₂ with irregular particles was well-distributed on the surface of the MXene. The desalination capacity of 30.5 mg·g⁻¹ is achieved at a voltage window of 1.2 V, which was higher than that of the reported pure MXene and MnO₂. The electrical double-layer (EDL) capacitive and the diffusion-controlled processes are the main charge storage mechanisms, and the EDL contribution provides 50.3% to the total capacitance. This result suggests a promising direction for further applying a MnO₂/MXene composite in CDI. Full article

This study proposed a biocompatible polymeric organic material-based synaptic transistor gated with a biopolymer electrolyte. A polyvinyl alcohol (PVA):chitosan (CS) biopolymer blended electrolyte with high ionic conductivity was used as an electrical double layer (EDL). It served as a gate insulator with a key function as an artificial synaptic transistor. The frequency-dependent capacitance characteristics of PVA:CS-based biopolymer EDL were evaluated using an EDL capacitor (Al/PVA: CS blended electrolyte-based EDL/Pt configuration). Consequently, the PVA:CS blended electrolyte behaved as an EDL owing to high capacitance (1.53 µF/cm²) at 100 Hz and internal mobile protonic ions. Electronic synaptic transistors fabricated using the PVA:CS blended electrolyte-based EDL membrane demonstrated basic artificial synaptic behaviors such as excitatory post-synaptic current modulation, paired-pulse facilitation, and dynamic signal-filtering functions by pre-synaptic spikes. In addition, the spike-timing-dependent plasticity was evaluated using synaptic spikes. The synaptic weight modulation was stable during repetitive spike cycles for potentiation and depression. Pattern recognition was conducted through a learning simulation for artificial neural networks (ANNs) using Modified National Institute of Standards and Technology datasheets to examine the neuromorphic computing system capability (high recognition rate of 92%). Therefore, the proposed synaptic transistor is suitable for ANNs and shows potential for biological and eco-friendly neuromorphic systems. Full article

MoS₂ nanomaterials and ionic liquids (ILs) have attracted tremendous interest as the prime electrodes and electrolytes of supercapacitors. However, the corresponding charge storage mechanisms have not yet been clearly understood. Herein, we study the molecular-level energy storage mechanisms of the MoS₂ electrode in imidazolium ionic liquid ([BMI⁺][PF₆⁻]) using molecular dynamics (MD) simulation. The electric double-layer (EDL) structures of MoS₂ electrodes in [BMI⁺][PF₆⁻] electrolytes are comprehensively studied in terms of number density, MD snapshots, separation coefficient, and ion-electrode interaction energy. Based on this, the electric potential and electric field distributions are calculated by integrating Poisson equations. Importantly, a bell-shaped differential capacitance profile is proposed, different from the U-shaped curve from the conventional Gouy–Chapman theory. Especially, it can be well reproduced by the differential charge density curve in the Helmholtz layer. This indicates that the capacitive behaviors of the MoS₂ electrode are primarily determined by the counterion population/structure in the EDL region 5.0 Å from the electrode surface. In the end, ion diffusion coefficients within different interfacial EDL regions are evaluated, revealing that dynamics are significantly suppressed by ~50% in the Helmholtz region. However, the dynamics can be recovered to a bulk state with the ion position 10 Å away from the electrode surface. The as-obtained insights reveal the charge storage mechanisms of MoS₂ in ILs, which can provide useful guidance on improving the energy density of MoS₂ supercapacitors. Full article

In this study, we fabricated an electric double-layer transistor (EDLT), a synaptic device, by preparing a casein biopolymer electrolyte solution using an efficient microwave-assisted synthesis to replace the conventional heating (heat stirrer) synthesis. Microwave irradiation (MWI) is more efficient in transferring energy to materials than heat stirrer, which significantly reduces the preparation time for casein electrolytes. The capacitance–frequency characteristics of metal–insulator–metal configurations applying the casein electrolyte prepared through MWI or a heat stirrer were measured. The capacitance of the MWI synthetic casein was 3.58 μF/cm² at 1 Hz, which was higher than that of the heat stirrer (1.78 μF/cm²), confirming a stronger EDL gating effect. Electrolyte-gated EDLTs using two different casein electrolytes as gate-insulating films were fabricated. The MWI synthetic casein exhibited superior EDLT electrical characteristics compared to the heat stirrer. Meanwhile, essential synaptic functions, including excitatory post-synaptic current, paired-pulse facilitation, signal filtering, and potentiation/depression, were successfully demonstrated in both EDLTs. However, MWI synthetic casein electrolyte-gated EDLT showed higher synaptic facilitation than the heat stirrer. Furthermore, we performed an MNIST handwritten-digit-recognition task using a multilayer artificial neural network and MWI synthetic casein EDLT achieved a higher recognition rate of 91.24%. The results suggest that microwave-assisted casein solution synthesis is an effective method for realizing biocompatible neuromorphic systems. Full article

Solvents have been considered to show a profound influence on the charge storage of electric double-layer capacitors (EDLCs). However, the corresponding mechanisms remain elusive and controversial. In this work, the influences of solvent dipole moment on the EDL structures, kinetic properties, and charging mechanisms of graphene-based EDLCs are investigated with atomistic simulations. Specifically, electrolyte structuring is conspicuously modulated by solvents, where a sharp increment of capacitance (~325.6%) and kinetics (~10-fold) is documented upon the slight descent of polarity by ~33.0%. Unusually, such an impressive enhancement is primarily attributed to the suppressed interfacial electric fields stimulated by strong-polarity solvents in the proximity of electrodes, which goes beyond the previously observed issues that stemmed from the competitive interplays between ions and solvents. Moreover, a distinctive polarity-dependent charging mechanism (i.e., from pure counterion adsorption to coion desorption) is identified, which for the first time delineates the pivotal role of solvent polarity in manipulating the charge storage evolutions. The as-obtained findings highlight that exploiting the solvent effects could be a promising avenue to further advance the performances of EDLCs. Full article

In this study, we propose the use of artificial synaptic transistors with coplanar-gate structures fabricated on paper substrates comprising biocompatible and low-cost potato-starch electrolyte and indium–gallium–zinc oxide (IGZO) channels. The electrical double layer (EDL) gating effect of potato-starch electrolytes enabled the emulation of biological synaptic plasticity. Frequency dependence measurements of capacitance using a metal-insulator-metal capacitor configuration showed a 1.27 μF/cm² at a frequency of 10 Hz. Therefore, strong capacitive coupling was confirmed within the potato-starch electrolyte/IGZO channel interface owing to EDL formation because of internal proton migration. An electrical characteristics evaluation of the potato-starch EDL transistors through transfer and output curve resulted in counterclockwise hysteresis caused by proton migration in the electrolyte; the hysteresis window linearly increased with maximum gate voltage. A synaptic functionality evaluation with single-spike excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), and multi-spike EPSC resulted in mimicking short-term synaptic plasticity and signal transmission in the biological neural network. Further, channel conductance modulation by repetitive presynaptic stimuli, comprising potentiation and depression pulses, enabled stable modulation of synaptic weights, thereby validating the long-term plasticity. Finally, recognition simulations on the Modified National Institute of Standards and Technology (MNIST) handwritten digit database yielded a 92% recognition rate, thereby demonstrating the applicability of the proposed synaptic device to the neuromorphic system. Full article

Analyzing the electrical double layer (EDL) in electrical impedance spectroscopy (EIS) measurement at low frequencies remains a challenging task for sensing purposes. In this work, we propose two approaches to deal with the EDL in measuring impedance for particles and non-adherent cells in an electrolytic suspension. The first approach is a simple procedure to compute a normalized electrical impedance spectrum named dispersed medium index (${\mathrm{DM}}_{\mathrm{i}}$). The second is the EIS modeling through an equivalent electric circuit based on the so-called effective capacitance (${\mathrm{C}}_{\mathrm{ef}}$), which unifies the EDL phenomena. Firstly, as an experiment under controlled conditions, we examine polymer particles of 6, 15, and 48 μm in diameter suspended in a 0.9% sodium chloride solution. Subsequently, we used K-562 cells and leukocytes suspended in a culture medium (RPMI-1640 supplemented) for a biological assay. As the main result, the ${\mathrm{DM}}_{\mathrm{i}}$ is a function of the particle concentration. In addition, it shows a tendency with the particle size; regardless, it is limited to a volume fraction of 0.03 × 10⁻⁴ to 58 × 10⁻⁴. The ${\mathrm{DM}}_{\mathrm{i}}$ is not significantly different between K-562 cells and leukocytes for most concentrations. On the other hand, the ${\mathrm{C}}_{\mathrm{ef}}$ exhibits high applicability to retrieve a function that describes the concentration for each particle size, the K-562 cells, and leukocytes. The ${\mathrm{C}}_{\mathrm{ef}}$ also shows a tendency with the particle size without limitation within the range tested, and it allows distinction between the K-562 and leukocytes in the 25 cells/µL to 400 cells/µL range. We achieved a simple method for determining an ${\mathrm{C}}_{\mathrm{ef}}$ by unifying the parameters of an equivalent electrical circuit from data obtained with a conventional potentiostat. This simple approach is affordable for characterizing the population of non-adherent cells suspended in a cell culture medium. Full article

With the increasing global water shortage issue, the development of water desalination and wastewater recycling technology is particularly urgent. Capacitive deionization (CDI), as an emerging approach for water desalination and ion separation, has received extensive attention due to its high ion selectivity, high water recovery, and low energy consumption. To promote the further application of CDI technology, it is necessary to understand the latest research progress and application prospects. Here, considering electric double layers (EDLs) and two typical models, we conduct an in-depth discussion on the ion adsorption mechanism of CDI technology. Furthermore, we provide a comprehensive overview of recent advances in CDI technology optimization research, including optimization of cell architecture, electrode material design, and operating mode exploration. In addition, we summarize the development of CDI in past decades in novel application fields other than seawater desalination, mainly including ionic pollutant removal, recovery of resource-based substances such as lithium and nutrients, and development of coupling systems between CDI and other technologies. We then highlight the most serious challenges faced in the process of large-scale application of CDI. In the conclusion and outlook section, we focus on summarizing the overall development prospects of CDI technology, and we discuss the points that require special attention in future development. Full article