Fabrication of MnS/GO/PANI nanocomposites on a highly conducting graphite electrode for supercapacitor application

Carbon-based materials (CBMs) have shown great versatility because they can be chemically combined with other materials for various applications. Chemical modification of CBMs can be achieved via covalent or non-covalent interactions. Non-covalent interactions are weak and fragile, causing structural change and molecule dissociation. Therefore, in this review, we summarize the covalent modification of CBMs via organic chemistry techniques, aiming at forming more robust and stable CBMs. Besides, their application as electrode materials in energy storage systems is also within the scope of this review. Covalent binding of redox-active organic molecules with CBMs improves the transfer rate of electrons and prevents the dissolution of redox-active molecules, resulting in good conductivity and cycle life. Numerous papers on the functionalization of CBMs have been published to date, but some of them lack scientific evidence and are unable to understand from chemistry viewpoint. Reliable articles with adequate evidence are summarized in this review from a synthetic chemistry viewpoint.

Covalent functionalization of carbon materials with redox-active organic molecules for energy storage

Graphene represents a new generation of materials which exhibit unique physicochemical properties such as high electron mobility, tunable optics, a large surface to volume ratio, and robust mechanical strength. These properties make graphene an ideal candidate for various optoelectronic, photonics, and sensing applications. In recent years, numerous efforts have been focused on azobenzene polymers (AZO-polymers) as photochromic molecular switches and thermal sensors because of their light-induced conformations and surface-relief structures. However, these polymers often exhibit drawbacks such as low photon storage lifetime and energy density. Additionally, AZO-polymers tend to aggregate even at moderate doping levels, which is detrimental to their optical response. These issues can be alleviated by incorporating graphene derivatives (GDs) into AZO-polymers to form orderly arranged molecules. GDs such as graphene oxide (GO), reduced graphene oxide (RGO), and graphene quantum dots (GQDs) can modulate the optical response, energy density, and photon storage capacity of these composites. Moreover, they have the potential to prevent aggregation and increase the mechanical strength of the azobenzene complexes. This review article summarizes and assesses literature on various strategies that may be used to incorporate GDs into azobenzene complexes. The review begins with a detailed analysis of structures and properties of GDs and azobenzene complexes. Then, important aspects of GD-azobenzene composites are discussed, including: (1) synthesis methods for GD-azobenzene composites, (2) structure and physicochemical properties of GD-azobenzene composites, (3) characterization techniques employed to analyze GD-azobenzene composites, and most importantly, (4) applications of these composites in various photonics and thermal devices. Finally, a conclusion and future scope are given to discuss remaining challenges facing GD-azobenzene composites in functional science engineering.

Strategies for Incorporating Graphene Oxides and Quantum Dots into Photoresponsive Azobenzenes for Photonics and Thermal Applications.

Stimuli‐responsive supercapacitors have attracted broad interest in constructing self‐powered smart devices. However, due to the demand for high cyclic stability, supercapacitors usually utilize stable or inert electrode materials, which are difficult to exhibit dynamic or stimuli‐responsive behavior. Herein, this issue is addressed by designing a MoS2@carbon core‐shell structure with ultrathin MoS2 nanosheets incorporated in the carbon matrix. In the three‐electrode system, MoS2@carbon delivers a specific capacitance of 1302 F g−1 at a current density of 1.0 A g−1 and shows a 90% capacitance retention after 10 000 charging‐discharging cycles. The MoS2@carbon‐based asymmetric supercapacitor displays an energy density of 75.1 Wh kg−1 at the power density of 900 W kg−1. Because the photo‐generated electrons can efficiently migrate from MoS2 nanosheets to the carbon matrix, the assembled photo‐responsive supercapacitor can answer the stimulation of ultraviolet‐visible‐near infrared illumination by increasing the capacitance. Particularly, under the stimulation of UV light (365 nm, 0.08 W cm−2), the device exhibits a ≈4.50% (≈13.9 F g−1) increase in capacitance after each charging‐discharging cycle. The study provides a guideline for designing multi‐functional supercapacitors that serve as both the energy supplier and the photo‐detector.

In Situ Generation of Ultrathin MoS2 Nanosheets in Carbon Matrix for High Energy Density Photo‐Responsive Supercapacitors

The demand for producing the sustainable energy resources has been efficiently increasing due to the rapid consumption of fossil fuels and world's population explosion. The storage of these resources plays an important role for future generation electronics. The solar energy storage is accomplished by pairing of two distinct devices, (i) the device that captures solar light and converts it into electrical energy such as solar cell/photovoltaic cell, and (ii) the device which stores this produced electrical energy such as electrochemical capacitor or supercapacitor. These two individual devices can be coupled to develop a photovoltaic cell integrated supercapacitor, known as solar electrochemical capacitor, which can be more preferable due to its unique properties like enhanced electrochemical performance giving high specific capacitance, high energy and power density. The present paper mainly reviews the solar electrochemical capacitor development, its present scenario, different active materials used, adapting different synthesis methods, different electrolytes and its performance that gives improved efficiency in a low cost is discussed. Finally, the challenges involved in coupling the individual devices, enhancing specific capacitance, maintain good cyclic stability and future scope is discussed.

The prospects and challenges of solar electrochemical capacitors

Azobenzene derivatives have fast light response characteristics; in this paper, a new azobenzene derivative (Azo) was synthesized and to be made a composite (PANI/GO/Azo) with polyaniline/graphene oxide (PANI/GO). Both composites were carefully investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Moreover, their electrochemical properties were characterized by the electrochemical workstation, including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), cycling stability, and electrochemical impedance spectroscopy (EIS). The results demonstrated that the PANI/GO/Azo composite has a higher capacitance of 478.3 F g−1 than that of PANI/GO (359.9 F g−1) at a current density of 1 A g−1. PANI/GO/Azo composite showed excellent photosensitive electrochemical properties under UV irradiation, and its rate of capacitance change achieved about 52.57%. Additionally, the PANI/GO/Azo composite also displayed high reversibility, with specific capacitance retention of 92% after 500 cycles. Therefore, the PANI/GO/Azo electrode with a controllable electrochemical performance by UV irradiation had a great potential in the photoresponsive supercapacitor.

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Synthesis of Polyaniline/Graphene Oxide/Azobenzene Composite and Its Adjustable Photoelectric Properties

Multi-stimuli-responsive hydrogels are intelligent materials that present advantages for application in soft devices compared with conventional machines. In this paper, we prepared a bilayer hydrogel consisting of a poly(2-(dimethylamino)ethyl methacrylate) layer and a poly(N-isopropylacrylamide) layer. The hydrogel responded to temperature, pH, NaCl, and ethanol by undergoing bending deformation. At 40 °C, it only took 23 s for the hydrogel to bend nearly 300°. Carbon black was also introduced into the hydrogel network to render it conductive. Based on its multi-stimuli-responsive properties and conductivity, the hydrogel was used to construct a 4-arm gripper, thermistor, and finger movement monitor. The time required to grip and release an object was 141 s. The resistance changed with temperature, which affected the brightness of an LED. Finger motions were monitored, and the bending angle could be distinguished.

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Multi-responsive and conductive bilayer hydrogel and its application in flexible devices

In this work, a sulfhydryl-functionalized azobenzene derivative (Azo) was synthesized and polyaniline/silver was modified (PANI/Ag) to make a nanocomposite (PANI/Ag/Azo). A series of characterization techniques like1HNMR, UV-vis absorption spectra, Raman spectra, FT-IR, XRD, SEM, TEM, and TGA was employed to study Azo, PANI/Ag, and PANI/Ag/Azo. Electrochemical properties were measured by cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD). CV showed that UV and blue light had hardly any effect on PANI/Ag. However, with the prolonged exposure time of UV light, the maximum CV current density of PANI/Ag/Azo rose from 1.24 to 2.72 A g-1. Then, after 20 min of blue light irradiation, the maximum current density gradually recovered (from 2.72 to 1.26 A g-1). The GCD also obtained similar results. After formula calculation, the specific capacitance of PANI/Ag/Azo also presented a reversible trend under the alternating irradiation of UV light and blue light. All the results show that PANI/Ag/Azo has a good photoelectric response, and its electrochemical performance can be reversibly adjusted by light. This result provides a new design idea for developing electrode materials with real-time electrochemical properties.

A Sulfhydryl Azobenzene-Modified Polyaniline/Silver Electrode and Its Photoswitching Electrochemical Performance.

A Low-modulus, Adhesive, and Highly Transparent Hydrogel for Multi-use Flexible Wearable Sensors

Coal gasification fine slag (CGFS) is a by-product of gasification process of gasification beds that pollutes the environment. To make the utilization of CGF more efficient, poly (vinyl chloride) (PVC)/CGFS composites were prepared via a melt blending process, and their mechanical and thermal properties were investigated. In order to dig deeper into the decomposition mechanism, the thermal degradation kinetics were systematically analyzed by drawing non-isothermal heat maps based on the Flynn-Wall-Ozawa, Friedman, and Kissinger model-free methods. According to the results, the properties of all tests vary significantly with CGFS content. In particular, at a the CGFS content of 20 phr, the tensile strength (tensile modulus) and flexural strength (flexural modulus) of CGFS-20 were 13.5% (47.8%) and 13.9% (41.6%) higher, respectively, than those of conventional CGFS-0 composites. However, the impact strength decreases with the increase of CGFS content. At the same time, the addition of CGFS suppresses the mass conversion rate and improves the thermal stability of PVC composites at high temperature, and the final residual mass reaches 31%, which is 12.7% higher than that of pure PVC. The kinetic analysis of thermal decomposition shows that CGFS promotes the initial degradation of the composites reduces the activation energy of the reaction, and at the same time endows them with higher thermal stability in the high-temperature phase.

Yanhua Teng

Papers

Synthesis of Polyaniline/Graphene Oxide/Azobenzene Composite and Its Adjustable Photoelectric Properties

Multi-responsive and conductive bilayer hydrogel and its application in flexible devices

A Sulfhydryl Azobenzene-Modified Polyaniline/Silver Electrode and Its Photoswitching Electrochemical Performance.

A Low-modulus, Adhesive, and Highly Transparent Hydrogel for Multi-use Flexible Wearable Sensors

Kinetic study of mechanical and thermal properties and thermal degradation of PVC composites based on coal gasification fine slag