Abstract

Inspired by the desire to solve the energy-related issues in remote sensing applications, internet of things, wireless autonomous devices, and self-powered portable electronic devices, triboelectric nanogenerators (TENGs) have been highly promoted. However, for use in the specified applications, especially in wearable and biomedical devices, environmental-friendly materials are required. Herein, an eco-friendly pectin polymer is used as a positive triboelectric material to fabricate a TENG with excellent output performance. Working in conjunction with a polyimide, the polyimide and microarchitected pectin (MA@pectin) polymer film-based TENG (PP-TENG) generated open circuit voltage (VOC), short circuit current (ISC), and charge density (QSC) of ∼300 V, 14 μA, and 70 μC cm−2, respectively, exhibiting remarkable enhancement compared to the TENG based on polyimide/pristine pectin polymer (VOC, ISC, and QSC of 170 V, 7.6 μA, and 47 μC cm−2, respectively) under similar operating conditions. The output performance of the PP-TENG is particularly reliant on the pectin concentration, indicating an optimum concentration of 9 wt%. The improved performance of the PP-TENG was systematically analyzed and explained in terms of pectin concentration, dielectric constant, and surface roughness. Furthermore, the PP-TENG can power portable electronic devices and light-emitting diodes to prove the capability of the TENG in practical applications. The fabricated PP-TENG is anticipated to be a sustainable energy harvester via a low-cost and facile approach.

Abstract

We demonstrate a wearable fabric-based energy harvester (Fab-EH) to hybridize a triboelectric generator (TrG) and a thermoelectric generator (ThG). Using a liquid-phase aluminum (Al) coating technique, we fabricate Al-coated fabrics with high electrical and thermal conductivity while maintaining the original texture. By adopting the Al-coated fabric material as both the electrodes of the TrG and the heat-transport layer of the ThG, the fabricated Fab-EH effectively scavenges electrical energy from body motion and body heat. The Fab-EH charges a storage capacitor with capacitance of 3.3 mF to 3 V within 240 sec with the designed transforming system. Moreover, a smartphone can be partially charged using the harvested energy. The Fab-EH thus has the potential to alleviate the recharging issue for portable and wearable devices.

Abstract

Triboelectric nanogenerators (TENGs) are gaining tremendous interest due to their versatile applications and energy harvesting ability. Besides, TENG would be useful for boimedical applications if the triboelectric materials used in the nanogenerator fabrication are non-toxic, biodegradable, and biocompatible. Herein, biocompatible triboelectric fibrous films were prepared via an electrospinning technique. The prepared fibrous tribofilms were employed to fabricate a triboelectric energy harvester and sensor (TEHS). A biocompatible study conducted on the electrospun positive and negative triboelectric films and the substrate reveals that the films are non-toxic and biocompatible. The effect of electrical output performance with respect to various bio-triboelectric materials was systematically studied and optimized. The TEHS, which is lightweight, flexible, scalable, and robust, has a low fabrication processing cost and can be used under various operational conditions. The proposed device had a very quick response time of 1.7 ms, creating a competitive advantage in healthcare monitoring. Multiple TEHS devices were fabricated to be integrated with the healthcare monitoring system. Finally, the proposed TEHS was used to harvest various mechanical energies and power portable electronics. Additionally, the TEHS can be attached to various health monitoring locations to monitor the patient’s physical movement.

Abstract

Strong orange-red-emitting Ba2LaTaO6:Eu3+ phosphors were designed and applied in various optical applications of luminescence lifetime thermometer, anti-counterfeiting film, and solid-state lighting applications. The crystal structure, elemental composition, asymmetry ratio, and other luminescent behaviors were investigated in detail. Especially, the optimal Ba2LaTaO6:0.1Eu3+ phosphor presented remarkable quantum yield (45.29%) and thermal stability (71.52% at 423 K). Based on the temperature-dependent luminescence decay curves, the maximum relative sensing sensitivity was 0.185 × 10−2 K−1 at 513 K. In addition, a novel anti-counterfeiting technique was introduced. The fabricated polydimethylsiloxane films exhibited three different colors under the irradiations of room light, 254 nm light, and 365 nm light, respectively. Eventually, the packaged light-emitting diode displayed the pure orange-red emission. Briefly, a series of the Eu3+-activated Ba2LaTaO6 phosphors with excellent luminescent properties were characterized and further applied in several optical fields for the first time.

Abstract

In this report, binder-free ultrathin nanosheet arrays of Co2FeSe4 (CFS) are prepared for the first time via the potentiostatic electrodeposition method for three minutes. Various physiochemical characterizations are performed to study the effect of Co and Fe in CoxFe3-xSe4. Ultrathin porous nanosheet arrays of the optimized CFS-2 (using 2 mmol CoCl2·6H2O) facilitate the electrolytic diffusion to the core electroactive sites, resulting in enhanced capacitive property of the electrode. As per the obtained results, the as-prepared CFS-2 delivers the maximum areal capacitance of 3393 mF cm−2 at a current density of 3 mA cm−2 in 1 M KOH with excellent capacitance retention of 96.4% even after 10,000 charge-discharge cycles. Furthermore, the CFS-2 is employed to fabricate poly(vinyl alcohol)-KOH gel electrolyte-based quasi-solid-state asymmetric supercapacitor device. The fabricated supercapacitor exhibits outstanding energy and power densities of 157.3 mWh cm−2 and 2250 mW cm−2, respectively and demonstrates excellent long cycling stability (85.8% capacitance retention) and columbic efficiency (101.8%) after 10,000 charge-discharge cycles. The overall three-minute electrodeposition synthesis enabling facile upscale route and excellent electrochemical properties suggests the potential of CFS-2 to be applicable in advanced energy storage systems and portable electronics.

Open AccessArticle

Unraveling the Role of Polydopamines in Resistive Switching in Al/Polydopamine/Al Structure for Organic Resistive Random-Access Memory

Jonghyeon Yun

1,2 and

Daewon Kim

2,3,*

Department of Electronics and Information Convergence Engineering, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin 17104, Korea

Institute for Wearable Convergence Electronics, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin 17104, Korea

Department of Electronic Engineering, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin 17104, Korea

Author to whom correspondence should be addressed.

Polymers 2022, 14(15), 2995; https://doi.org/10.3390/polym14152995

Submission received: 16 June 2022 / Revised: 6 July 2022 / Accepted: 21 July 2022 / Published: 24 July 2022

(This article belongs to the Section Polymer Applications)

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Abstract

In an era of rapidly evolving artificial intelligence and 5G communications technologies, massive data storage and processing are required for the real-time operation of digital processors in conventional wearable devices. However, classical von-Neumann architecture computers are limited by bottleneck-related issues. As a solution, resistive random-access memory (RRAM) devices are being considered as next generation in-memory computing devices. Among various materials, a polydopamine (PDA) is an attractive candidate for the fabrication of wearable and flexible RRAM devices. Herein, an aluminum/PDA/aluminum structure is proposed to investigate the influence of the PDA layer on resistive switching. The resistance-switching characteristics of an Al/PDA/Al structure are investigated by changing the PDA’s coating time and an on/off ratio of 2.48 × 103 is recorded. X-ray photoelectron spectroscopy reveals the presence of an Al2O3 layer in Al/PDA/Al structure, and the contents of oxygen vacancies are changed according to PDA coating time. Conductive filaments in the PDA/Al structure are confirmed by conductive atomic-force microscopy. As an application, a flexible Al/PDA/Al structure is fabricated using polyethylene terephthalate substrate and its operation is successfully confirmed. These results describe the resistive-switching characteristics, including oxygen vacancies, of Al/PDA/Al structures and provide new ways of understanding the resistive-switching mechanism of PDA-based RRAM devices.

Keywords:

organic resistance random-access memory; polydopamine; resistive switching; oxygen vacancy

Summary

The approach to accomplishing long cycle solidity usually depends on the electrode materials in lithium-ion batteries (LIBs). Herein, mesoporous FeVO4 (MFVO) nanostructures (NSs) were prepared via a simple hydrothermal method and post-calcination using different concentrations of ethylenediaminetetraacetic acid (EDTA) chelating agent. The morphology, microstructure, and mesoporous nature of the as-prepared samples were characterized by scanning electron microscope, transmission electron microscope, and Brunauer-Emmett-Teller analyses, respectively. The as-obtained MFVO NSs were examined as a negative material for LIBs. The enhanced MFVO-2 (0.2 g of EDTA) electrode provides an initial charge/discharge capacity of 2880 mA h g−1/2707 mA h g−1 at 0.1 A g−1. Even after 100 cycles, it displays a superior specific discharge capacity of 906 mA h g−1. Furthermore, the MFVO-2 electrode exhibits a high-rate performance with a steady reversible capacity. As a result, the porosity and density of nanorod-like morphologies are significant factors in their electrochemical performances. The outstanding electrochemical effects of MFVO NSs may be suggested as a prospective anode material for enhanced LIBs.

Summary

Recently, multiple transition metal oxide-based materials have been intensely attracted in the field of energy storage owing to their multifunctional properties. Meanwhile, carbon-based materials are considered more reliable electrode candidates due to their high porosity and chemical stability. Herein, we synthesized carbon-embedded transition multimetal oxides as a hybrid composite by a facile hydrothermal method, followed by annealing in inert medium. The effect of different metal ion species (Ni, Co, and Ce) and their combination on the energy storage performance was explored. The carbon-embedded Ni-Co-Ce-Si (C/NiCoCeSi) oxide electrode revealed a higher areal capacity of 35.5 μAh/cm2 at a current density of 3 mA/cm2 than the C/NiSi oxide and C/NiCoSi oxide electrodes due to the improved redox chemistry. Moreover, the C/NiCoCeSi oxide electrode was subjected to a test involving 10 000 charge-discharge cycles at 7 mA/cm2, and it demonstrated the decent capacity retention of 83.8%. Furthermore, the C/NiCoCeSi oxide material was used as a positive electrode in the fabrication of a hybrid cell (HC). The as-fabricated HC demonstrated a good areal capacitance of 105.9 mF/cm2 at 1.5 mA/cm2 with maximum energy and power densities of 29.2 μWh/cm2 and 6350 μW/cm2, respectively. Finally, the HC also powered light-emitting diodes to test its practical functionality.

Abstract

Exploring a novel electrode material with a rational composition/nanostructure design is a general strategy to fabricate the high-performance electrodes for supercapacitors (SCs). Clay mineral materials including montmorillonite are potential electrode materials owing to their inherently porous structure, high specific surface area, and environmental friendliness. Nevertheless, low electronic conductivity limits the application of montmorillonite alone as a high-performance electrode for SCs. Thus, it is essential to improve the surface conductivity by additional modification with metal sources. In this work, an advanced battery-type electrode is suggested based on montmorillonite as a template to enable the hierarchical growth of nickel telluride (NiTe) nanostructures with considerable porosity. Given their abundant micro-porous structure and high specific surface area, different compositions have been employed by varying the Ni and Te contents to understand the effect of coordination on electrochemical performance. It was found that the optimized composition of montmorillonite-based micro-nanostructure with 75% Ni and 25% Te (C-MN0.75T0.25) improves the specific surface area, allowing easy adsorption/desorption of electrolytic ions. With a high specific capacity, superior electrochemical performance was successfully demonstrated in a three-electrode configuration. Additionally, the assembled hybrid supercapacitor (HSC) device along with a capacitive-type electrode possessed excellent capacitance, long-term endurance, high energy, and power densities, exhibiting the desired properties of an energy storage system. This study paves the way toward the development of simple and low-cost clay-based electrodes for energy storage applications.

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Unraveling the Role of Polydopamines in Resistive Switching in Al/Polydopamine/Al Structure for Organic Resistive Random-Access Memory

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