Novel enzyme-free multifunctional bentonite/polypyrrole/silver nanocomposite sensor for hydrogen peroxide detection over a wide pH range

Precise designs of low-cost and efficient catalysts for the detection of hydrogen peroxide (H2O2) over wide ranges of pH are important in various environmental applications. Herein, a versatile and ecofriendly approach is presented for the rational design of ternary bentonite-silylpropyl-polypyrrole/silver nanoarchitectures (denoted as BP-PS-PPy/Ag) via the in-situ photo polymerization of pyrrole with salinized bentonite (BP-PS) in the presence of silver nitrate. The Pyrrolyl-functionalized silane (PS) is used as a coupling agent for tailoring the formation of highly exfoliated BP-PS-PPy sheet-like nanostructures ornamented with monodispersed Ag nanoparticles (NPs). Taking advantage of the combination between the unique physicochemical properties of BP-PS-PPy and the outstanding catalytic merits of Ag nanoparticles (NPs), the as-synthesized BP-PS-PPy/Ag shows a superior electrocatalytic reduction and high-detection activity towards H2O2 under different pH conditions (from 3 to 10). Intriguingly, the UV-light irradiation significantly enhances the electroreduction activity of H2O2 substantially, compared with the dark conditions, due to the high photoelectric response properties of Ag NPs. Moreover, BP-PS-PPy/Ag achived a quick current response with a detection limit at 1 μM within only 1 s. Our present approach is green, facile, scalable and renewabl

Hybrid polypyrrole and polydopamine nanosheets for precise Raman/photoacoustic imaging and photothermal therapy

The development of near-infrared light (NIR)-responsive conductive polymers provides a useful theranostic platform for malignant tumours by maximizing spatial resolution with deep tissue penetration for diagnosis and photothermal therapy. Herein, we demonstrated the self-assembly of ultrathin two-dimensional (2D) polypyrrole nanosheets utilizing dopamine as a capping agent and a monolayer of octadecylamine as a template. The 2D polypyrrole-polydopamine nanostructure (DPPy) had tunable size distribution which showed strong absorption in the first and second near-infrared windows, enabling photoacoustic imaging and photothermal therapy. The hybrid double-layer was demonstrated to increase Raman intensity for 3D Raman imaging (up to two orders of magnitude enhancement and spatial resolution up to 1 μm). The acidic environment drove reversible doping of polypyrrole, which could be detected by Raman spectroscopy. The combined properties of the nanosheets could substantially enhance performance in dual-mode Raman and photoacoustic guided photothermal therapy, as shown by the 69% light to heat conversion efficiency and higher cytotoxicity against cancer spheroids. These pH-responsive features highlight the potential of 2D conductive polymers for applications in accurate, highly efficient theranostics

Engineering Nanostructured MnO2 for High Performance Supercapacitors

Manganese oxides (MnO2) have particularly received increasing attention owing to their high theoretical specific capacitance of 1370 F/g, low-cost, natural abundance, and environmental benignity. However, MnO2 suffers from low electrical conductivity (10−5 to 10−6 S/cm), low ionic diffusion constant (~10−13 cm2/V s), and low structural stability, which results in low electrochemical utilization and poor cycling life. It is therefore important to explore new strategies to improve the electrochemical performance of MnO2. The effective methods to maximize the performance involve (i) reducing MnO2 structures to a nanoscale range and (ii) compositing MnO2 with highly conductive materials. In this chapter, we will first introduce the rapid development of MnO2 nanostructures for supercapacitors. Then the fundamental charge storage mechanism of MnO2 will be specifically clarified. The preparation methods of MnO2 nanostructures and their composites will be subsequently summarized. Then, we will pay great attention to the most recent development of MnO2-based nanostructures for supercapacitors, which is the main body of this chapter. The practical application of MnO2 nanostructures for symmetric and asymmetric supercapacitors will be discussed. Finally, we will present a brief perspective regarding the rational design and synthesis of MnO2-based nanostructures

Patterning two-dimensional free-standing surfaces with mesoporous conducting polymers

The ability to pattern functional moieties with well-defined architectures is highly important in material science, nanotechnology and bioengineering. Although two-dimensional surfaces can serve as attractive platforms, direct patterning them in solution with regular arrays remains a major challenge. Here we develop a versatile route to pattern two-dimensional free-standing surfaces in a controlled manner assisted by monomicelle close-packing assembly of block copolymers, which is unambiguously revealed by direct visual observation. This strategy allows for bottom-up patterning of polypyrrole and polyaniline with adjustable mesopores on various functional free-standing surfaces, including two-dimensional graphene, molybdenum sulfide, titania nanosheets and even on one-dimensional carbon nanotubes. As exemplified by graphene oxide-based mesoporous polypyrrole nanosheets, the unique sandwich structure with adjustable pore sizes (5-20 nm) and thickness (35-45 nm) as well as enlarged specific surface area (85 m(2) g(-1)) provides excellent specific capacitance and rate performance for supercapacitors. Therefore, this approach will shed light on developing solution-based soft patterning of given interfaces towards bespoke functions

Hierarchical ultrathin NiAl layered double hydroxide nanosheet arrays on carbon nanotube paper as advanced hybrid electrode for high performance hybrid capacitors

To effectively improve the power density and rate capability of layered double hydroxide (LDH) based supercapacitors, a hybrid supercapacitor (HSC) comprising of hierarchical ultrathin NiAl-LDH nanosheet arrays on carbon nanotube paper (CNP-LDH) is developed with porous graphene nanosheets as the negative electrode for the first time. SEM image shows that hierarchical NiAl LDH nanosheet arrays are assembled by numerous ultrathin nanosheets with thickness of a few to tens of nanometers. Remarkably, with an operating voltage of 1.6 V, the HSC possesses a high energy density of 50.0 Wh kg-1 at an average power density of 467 W kg-1. Even at a fast discharging time of 3.9 s, a high energy density (23.3 Wh kg-1) could also be retained at a power density of 21.5 kW kg-1. Moreover, the HSC exhibits cycling stability with a retention rate of 78% after 5000-cycle charge-discharge test at 5 A g-1. The results inspire us to propose our high-performance CNP-LDH as a promising electrode for energy storage applications

Constructing pseudocapacitive electrodes for supercapacitors based on rationally designed nanoarchitectured current collectors

Supercapacitors are of high importance as electrochemical energy storage devices attributing to their outstanding power performance, excellent reversibility and long cycle life. However, compared with batteries, supercapacitors suffer from low energy density, which hinders their wide application. Pseudocapacitive materials with a high theoretical capacitance hold a great promise in boosting the energy storage capability for supercapacitors. Research on nanoarchitectured current collectors aims to reach their full potential in the field of charge storage by addressing challenging problems such as the inherently low electrical conductivity and the sluggish charge and discharge behavior of most pseudo-capacitive materials. In this regard, three kinds of nanoarchitectured current collectors, i.e., Ni nanorod arrays (NN), etched porous alumina membrane (EPAM) coated with SnO2 layer (EPAM@SnO2), and Ni nanowires confined into EPAM (NiNWs-EPAM), were designed to construct pseudocapacitive electrodes and they were investigated in different aspects: Firstly, the role of NN nanoarchitectured current collectors in supercapacitor electrodes with the pseudocapacitive materials in the case of high mass loading and thick layer is firstly evaluated. Through electrochemical performance and impedance analysis of the electrodes with and without the NN nanoarchitectured current collectors, the validation of thick-layer electrodes design based on nanoarchitectured current collectors is demonstrated. Secondly, EPAM@SnO2 scaffolds are designed and employed as nanoarchitectured current collectors for nanoelectrodes in order to improve the device energy density of the micro-supercapacitor (MSC). Owing to the oriented and robust nanochannels in EPAM@SnO2, the resultant nanoelectrodes can synergize both effective ion migration and abundant electroactive surface area within the limited footprint. A MSC is finally constructed and exhibits record high performance, suggesting the feasibility of the current design for energy storage devices. Thirdly, the NiNWs-EPAM nanoarchitectured current collector is fabricated to construct non-aggregative and robust one-dimensional (1D) nanoelectrode arrays. The EPAM prevents 1D nanoelectrode arrays from self-aggregating and meanwhile endows them with high structural integrity and electrochemical stability during device assembly and operation process. MSCs assembled with these non-aggregative and robust 1D nanoelectrodes attain remarkable energy storage performance. The achieved results within this work on nanoarchitectured current collectors for supercapacitors shed light on the design of future energy storage and conversion devices.Superkondensatoren sind als elektrochemische Energiespeicher von großer Bedeutung, was auf ihre hervorragende elektrische Leistung, ihre ausgezeichnete Reversibilität und ihre lange Lebensdauer zurückzuführen ist. Im Vergleich zu Batterien haben Superkondensatoren jedoch eine geringe Energiedichte, was ihre breite Anwendung einschränkt. Pseudokapazitive Materialien mit einer hohen theoretischen Kapazität sind sehr vielversprechend, um die Energiespeicherfähigkeit von Superkondensatoren zu erhöhen. Die Forschung an nanoarchitektonischen Stromspeichern zielt darauf ab, ihr volles Potenzial im Bereich der Ladungsspeicherung auszuschöpfen, indem man sich mit den herausfordernden Aspekten wie der inhärent niedrigen elektrischen Leitfähigkeit und dem trägen Lade- und Entladeverhalten der meisten pseudokapazitiven Materialien befasst. In diesem Zusammenhang wurden drei Arten von nanoarchitektonischen Stromkollektoren entworfen, um pseudokapazitive Elektroden zu konstruieren, die unter verschiedenen Aspekten untersucht werden sollten. Es handelt sich dabei um Nickel-Nanorod-Arrays (NN), geätzte poröse Aluminiumoxidmembranen (EPAM), die mit einer SnO2-Schicht beschichtet sind (EPAM@SnO2), und in EPAM eingeschlossene Nickel-Nanodrähte (NiNWs-EPAM): Zunächst wird die Rolle von NN-Nanoarchitekten-Stromkollektoren in Superkondensator-Elektroden mit den pseudokapazitiven Materialien bei hoher Massenbelastung und dicker Schicht bewertet. Durch die elektrochemische Leistungs- und Impedanzanalyse der Elektroden mit und ohne die NN-nanoarchitektierten Stromkollektoren wird die Validierung des Designs von Dickschichtelektroden auf der Basis von nanoarchitektierten Stromkollektoren demonstriert. Zweitens werden EPAM@SnO2-Gerüste als nanoarchitektonische Stromkollektoren für Nanoelektroden entworfen und eingesetzt, um die Energiedichte des Mikro-Superkondensators (MSC) zu verbessern. Dank der orientierten und robusten Nanokanäle in EPAM@SnO2 können die daraus resultierenden Nanoelektroden sowohl die effektive Ionenmigration als auch die sehr große elektroaktive Oberfläche innerhalb des begrenzten Footprints synergetisch nutzen. Ein MSC wird schließlich konstruiert und weist eine rekordverdächtig hohe Leistung auf, was auf die Umsetzbarkeit des derzeitigen Designs für Energiespeichervorrichtungen hindeutet. Drittens wird der NiNWs-EPAM nanoarchitektierte Stromkollektor hergestellt, um nicht aggregierende und robuste eindimensionale (1D) Nanoelektroden-Arrays zu konstruieren. Das EPAM verhindert die Selbstaggregation von 1D-Nanoelektroden-Arrays und verleiht ihnen gleichzeitig eine hohe strukturelle Integrität und elektrochemische Stabilität während der Montage und des Betriebsprozesses der Geräte. MSCs, die mit diesen nicht aggregierenden und robusten 1D-Nanoelektroden bestückt sind, erreichen eine bemerkenswerte Energiespeicherleistung. Die im Rahmen dieser Arbeit zu nanoarchitektonischen Stromkollektoren für Superkondensatoren erzielten Ergebnisse geben einen Ausblick auf den Entwurf zukünftiger Energiespeicher und -wandler

Graphene as a flexible electrode: review of fabrication approaches

In recent years, the technological advancement of supercapacitors has been increasing exponentially due to the high demand in electronic consumer products. As so, researchers have found a way to meet that demand by fabricating graphene. As developments are made toward the future, two big advancements to be made are large-scale fabrication of graphene and fabricating graphene as a flexible electrode. This would allow for use in larger products and for manipulation of the unique properties of graphene to accommodate superior design alternatives. While large scale production is still mentioned, this review is specifically focusing on different methods used to fabricate graphene as a flexible electrode. Various fabrication methods, such as Hummers\u27 method, chemical vapor deposition, epitaxial growth, and exfoliation of graphite oxide, used to fabricate graphene in such a way that allows flexibility and utilization of graphene\u27s mechanical and electrical properties are discussed. Additionally, a section on environmentally friendly fabrication approaches is presented and discussed