Influence of the Electrolyte Film Thickness on Charge Dynamics of Ionic Liquids in Ionic Electroactive Devices

Ordered patterns in electroactive polymer ionic liquid blends: effect of long range interactions

Designing multifunctional soft materials via pattern formation has been a major challenge for scientists and engineers. Soft materials based on polymers are the perfect candidates for designing such materials as they are not only easy to handle, but also offer diverse combinations of mechanical and chemical properties. Here, we present a polymer-based ternary system and reveal, using modelling and simulations, the mechanisms for creating patterned surfaces. Specifically, we consider polymer ionic liquid (PIL) blends and demonstrate that exposure to a uniform electric field results in the formation of ordered patterns through phase separation. Our approach is based on reaction-diffusion phenomena and utilizes Poisson-Boltzmann-Nernst-Planck equations to capture the long-range interactions of ionic liquids in both weak and strong segregation limits. Furthermore, we elucidate that the ordered patterns in our PIL blend can be tuned by changing the direction of the electric field. From the structural characterization point of view, we reveal that the presence of the electric field significantly enhances the domain growth rate and their respective ordering in a remarkable fashion. We believe this non-invasive technique is a significant step towards the development of ordered structures at microscopic length scales and can be utilized for micro-scale fabrication from soft materials.

Ultrafast Ion Transfer of Metal-Organic Framework Interface for Highly Efficient Energy Storage

Flexible supercapacitors are favorable for wearable electronics. However, their high-rate capability and mechanical properties are limited because of unsatisfactory ion transfer kinetics and interfacial modulus mismatch inside devices. Here, we develop a metal-organic framework interface with superior electrical and mechanical properties for supercapacitors. The interfacial mechanism facilitates ultrafast ion transfer with an energy barrier reduction of 43% compared with that of conventional transmembrane transport. It delivers high specific capacity at a wide rate range and exhibits ultrastability beyond 30000 charge-discharge cycles. Furthermore, meliorative modulus mismatch benefited from ultrathin interface design that improves mechanical properties of flexible supercapacitors. It delivers a stable energy supply under various mechanical conditions like bending and twisting status and displays ultrastable mechanical properties with performance retention of 95.5% after 10 000 bending cycles. The research paves the way for interfacial engineering for ultrastable electrochemical devices.

Field-Effect Transistor with a Plasmonic Fiber Optic Gate Electrode as a Multivariable Biosensor Device

A novel multivariable system, combining a transistor with fiber optic-based surface plasmon resonance spectroscopy with the gate electrode simultaneously acting as the fiber optic sensor surface, is reported. The dual-mode sensor allows for discrimination of mass and charge contributions for binding assays on the same sensor surface. Furthermore, we optimize the sensor geometry by investigating the influence of the fiber area to transistor channel area ratio and distance. We show that larger fiber optic tip diameters are favorable for electronic and optical signals and demonstrate the reversibility of plasmon resonance wavelength shifts after electric field application. As a proof of principle, a layer-by-layer assembly of polyelectrolytes is performed to benchmark the system against multivariable sensing platforms with planar surface plasmon resonance configurations. Furthermore, the biosensing performance is assessed using a thrombin binding assay with surface-immobilized aptamers as receptors, allowing for the detection of medically relevant thrombin concentrations.

Highly Sensitive Ultrastable Electrochemical Sensor Enabled by Proton-Coupled Electron Transfer

Electrochemical sensors are critical to artificial intelligence by virtue of capability of mimicking human skin to report sensing signals. But their practical applications are restricted by low sensitivity and limited cycling stability, which result from piezoionic mechanism with insufficient sensing response. Here, we report a highly sensitive ultrastable sensor based on proton-coupled electron transfer, which is different from piezoionic mechanism. The sensor gives a high sensing signal output of 117 mV, which is 16 times higher than that of counterpart device (7 mV). It delivers excellent working stability with performance retention as high as 99.13% over 10 000 bending cycles in air, exceeding that of the best-known sensors reported previously. The flexible sensor displays high sensitivity in detecting real-time signals of human activities with large and subtle deformations, including wrist bending, moving speed, pulse wave and voice vibration. Smart functions, such as braille language and handwriting recognitions, are demonstrated for artificial intelligence.

Two-Dimensional Nanosheets-Based Soft Electro-Chemo-Mechanical Actuators: Recent Advances in Design, Construction, and Applications

Soft electro-chemo-mechanical actuators have received enormous interest in biomimetic technologies, wearable electronics, and microelectromechanical systems due to their low voltage-driven large deformation, fast response, high strain, and working durability. Two-dimensional (2D) nanosheets, which can highly promote ion-induced micromotion to macrodeformation, have outstandingly been used as prime actuator electrodes because of their ordered microstructures, tunable interlayer spaces, controllable electrochemical activities, and excellent electrical and mechanical properties. Here, this review primarily focuses on the recent advances in key 2D electro-chemo-mechanical actuator electrodes, including graphene, MXenes, graphitic carbon nitride, molybdenum disulfide, black phosphorus, and graphdiyne. Various synthetic strategies of electrode design, such as microstructural architecture, active-site regulation, and channel construction, for achieving high ionic kinetic transport, charge storage, and electrochemical-mechanical performances are discussed. The advanced structures with diverse building principles that provide ordered and active ionic pathways for high actuation speed and strain are emphasized. Furthermore, the innovative applications of electro-chemo-mechanical actuators toward biomimetic robots and smart devices are highlighted. Finally, the current challenges and future perspectives are also proposed. The aim of this review is to provide the guiding significance for scientific researchers and industrial engineers to design higher performance next-generation electro-chemo-mechanical actuators.

High-Performance Hierarchical Black-Phosphorous-Based Soft Electrochemical Actuators in Bioinspired Applications

Bioinspired methods allowing artificial actuators to perform controllably are potentially important for various principles and may offer fundamental insight into chemistry and engineering. To date, the main challenges persist regarding the achievement of large deformation in fast response-time and potential-engineering applications in which electrode materials and structures limit ion diffusion and accumulation processes. Herein, a novel electrochemical actuator is developed that presents both higher electromechanical performances and biomimetic applications based on hierachically structured covalently bridged black phosphorous/carbon nanotubes. The new actuator demonstrates astonishing actuation properties, including low power consumption/strain (0.04 W cm^-2 %^-1 ), a large peak-to-peak strain (1.67%), a controlled frequency response (0.1-20 Hz), faster strain and stress rates (11.57% s^-1 ; 28.48 MPa s^-1 ), high power (29.11 kW m^-3 ), and energy (8.48 kJ m^-3 ) densities, and excellent cycling stability (500 000 cycles). More importantly, bioinspired applications such as artificial-claw, wings-vibrating, bionic-flower, and hand actuators have been realized. The key to high performances stems from hierachically structured materials with an ordered lamellar structure, large redox activity, and electrochemical capacitance (321.4 F g^-1 ) for ions with smooth diffusion and flooding accommodation, which will guide substantial progress of next-generation electrochemical actuators.

The Anionic Surfactant/Ionic Liquids Intercalated Reduced Graphene Oxide for High-performance Supercapacitors

The thermally reduced graphene oxide (TRG) composites with various interlayer distances were synthesized. These TRG sheets are intercalated with anionic surfactant sodium dodecyl sulfate (SDS) to prevent the restacking between TRG sheets. A facile approach is employed to enlarge the interlayer distance between the TRG sheets by the Coulomb force interaction between the intercalated surfactants and the ionic liquids. A systematic investigation of the morphology and the electrical performances of these EDLC cells was carried out. It was found that the energy density of the cells is improved from 34.9 to 61.8 Wh/kg at 1 A/g suggesting that the increased interlayer distance could enlarge the accessible surface area for the ionic liquid electrolyte.

Graphitic carbon nitride nanosheet electrode-based high-performance ionic actuator

Ionic actuators have attracted attention due to their remarkably large strain under low-voltage stimulation. Because actuation performance is mainly dominated by the electrochemical and electromechanical processes of the electrode layer, the electrode material and structure are crucial. Here, we report a graphitic carbon nitride nanosheet electrode-based ionic actuator that displays high electrochemical activity and electromechanical conversion abilities, including large specific capacitance (259.4 F g⁻¹) with ionic liquid as the electrolyte, fast actuation response (0.5±0.03% in 300 ms), large electromechanical strain (0.93±0.03%) and high actuation stability (100,000 cycles) under 3 V. The key to the high performance lies in the hierarchical pore structure with dominant size <2 nm, optimal pyridinic nitrogen active sites (6.78%) and effective conductivity (382 S m⁻¹) of the electrode. Our study represents an important step towards artificial muscle technology in which heteroatom modulation in electrodes plays an important role in promoting electrochemical actuation performance.

Electrochemical actuators store electric energy and generate mechanical motion. Here, the authors present an ionic actuator based on a hierarchically porous graphitic carbon nitride electrode, which exhibits high charge storage, fast actuation response, large electromechanical strain and high stability.