Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

Metal oxide nanostructures are promising electrode materials for lithium-ion batteries and supercapacitors because of their high specific capacity/capacitance, typically 2-3 times higher than that of the carbon/graphite-based materials. However, their cycling stability and rate performance still can not meet the requirements of practical applications. It is therefore urgent to improve their overall device performance, which depends on not only the development of advanced electrode materials but also in a large part "how to design superior electrode architectures". In the article, we will review recent advances in strategies for advanced metal oxide-based hybrid nanostructure design, with the focus on the binder-free film/array electrodes. These binder-free electrodes, with the integration of unique merits of each component, can provide larger electrochemically active surface area, faster electron transport and superior ion diffusion, thus leading to substantially improved cycling and rate performance. Several recently emerged concepts of using ordered nanostructure arrays, synergetic core-shell structures, nanostructured current collectors, and flexible paper/textile electrodes will be highlighted, pointing out advantages and challenges where appropriate. Some future electrode design trends and directions are also discussed.

Recent Advances in Metal Oxide-based Electrode Architecture Design for Electrochemical Energy Storage

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

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Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

In recent years, tremendous research effort has been aimed at increasing the energy density of supercapacitors without sacrificing high power capability so that they reach the levels achieved in batteries and at lowering fabrication costs For this purpose, two important problems have to be solved: first, it is critical to develop ways to design high performance electrode materials for supercapacitors; second, it is necessary to achieve controllably assembled supercapacitor types (such as symmetric capacitors including double-layer and pseudo-capacitors, asymmetric capacitors, and Li-ion capacitors) The explosive growth of research in this field makes this review timely Recent progress in the research and development of high performance electrode materials and high-energy supercapacitors is summarized Several key issues for improving the energy densities of supercapacitors and some mutual relationships among various effecting parameters are reviewed, and challenges and perspectives in this exciting field are also discussed This provides fundamental insight into supercapacitors and offers an important guideline for future design of advanced next-generation supercapacitors for industrial and consumer applications

Recent Advances in Design and Fabrication of Electrochemical Supercapacitors with High Energy Densities

Supercapacitors have attracted intense attention due to their great potential to meet the demand of both high energy density and power density in many advanced technologies. Various carbon-based nanocomposites are currently pursued as supercapacitor electrodes because of the synergistic effect between carbon (high power density) and pseudo-capacitive nanomaterials (high energy density). This feature article aims to review most recent progress on 3D (3D) carbon based nanostructures for advanced supercapacitor applications in view of their structural intertwinement which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The carbon nanostructures comprise of CNTs-based networks, graphene-based architectures, hierarchical porous carbon-based nanostructures and other even more complex carbon-based 3D configurations. Their advantages and disadvantages are compared and summarized based on the results published in the literature. In addition, we also discuss and view the ongoing trends in materials development for advanced supercapacitors.

3D carbon based nanostructures for advanced supercapacitors

In this paper, a very simple solution-based method is employed to coat amorphous MnO2 onto crystalline SnO2 nanowires grown on stainless steel substrate, which utilizes the better electronic conductivity of SnO2 nanowires as the supporting backbone to deposit MnO2 for supercapacitor electrodes. Cyclic voltammetry (CV) and galvanostatic charge/discharge methods have been carried out to study the capacitive properties of the SnO2/MnO2 composites. A specific capacitance (based on MnO2) as high as 637 F g−1 is obtained at a scan rate of 2 mV s−1 (800 F g−1 at a current density of 1 A g−1) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 50 A g−1 are 35.4 W h kg−1 and 25 kW kg−1, respectively, demonstrating the good rate capability. In addition, the SnO2/MnO2 composite electrode shows excellent long-term cyclic stability (less than 1.2% decrease of the specific capacitance is observed after 2000 CV cycles). The temperature-dependent capacitive behavior is also discussed. Such hi...

Facile Coating of Manganese Oxide on Tin Oxide Nanowires with High-Performance Capacitive Behavior

A novel 1D/1D nanocomposite-based photodetector is successfully fabricated from high-crystalline ZnS/ZnO biaxial nanobelts for the first time. Optimized performance of the ZnS/ZnO nanobelt photodetector is much better than that of pure ZnS or ZnO nanostructures, with a wide-range UV-A light photoresponse, high sensitivity, and very fast response speed.

An Optimized Ultraviolet‐A Light Photodetector with Wide‐Range Photoresponse Based on ZnS/ZnO Biaxial Nanobelt

Conducting nanowires are of particular interest in energy-related research on devices such as supercapacitors, batteries, water splitting electrodes and solar cells. Their direct electrode/current collector contact and highly conductive 1D structure enable conducting nanowires to provide ultrafast charge transportation. In this paper, we report the facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn2SnO4 (ZTO) and the application of this material to a supercapacitor. This study also presents the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure. This novel material demonstrates outstanding electrochemical performance with a high specific capacitance of 1805 F g−1 at 0.5 A g−1, and an excellent rate performance of 1275 F g−1 can be achieved at 100 A g−1. Furthermore, an asymmetric supercapacitor was successfully fabricated using active carbon as a negative electrode. This asymmetric device exhibits a high energy density of 23.7 W h kg−1 at a power density of 284.2 W kg−1. Meanwhile, a high power density of 5817.2 W kg−1 can be achieved at an energy density of 9.7 W h kg−1. More importantly, this device exhibits long-term cycling stability, with 92.7% capacity retention after 5000 cycles.

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Enhancing electrochemical reaction sites in nickel-cobalt layered double hydroxides on zinc tin oxide nanowires: a hybrid material for an asymmetric supercapacitor device.

In this work, monodisperse polydopamine (PDA) spheres with tunable diameters have been synthesized through a facile and low cost method using a deionized water and alcohol mixed solvent. The PDA spheres possess surface functional groups (-OH, -NH(2)), exhibiting an extraordinary versatile active nature. It is demonstrated that the PDA spheres could serve as an active template for the convenient synthesis of various nanostructures, e.g., MnO(2) hollow spheres or PDA/Fe(3)O(4) and PDA/Ag core/shell nanostructures. No surface modification or special treatment is required for the synthesis of these nanostructures, which makes the fabrication process simple and very convenient. The novel application of PDA/Fe(3)O(4) spheres as fillers in nanocomposites for high-performance capacitors is demonstrated, indicating a promising practicality. The PDA spheres provide a new general platform not only for the facile assembly of nanostructures but also a green synthetic template for practical applications.

Jian Yan

Papers

Facile Coating of Manganese Oxide on Tin Oxide Nanowires with High-Performance Capacitive Behavior

An Optimized Ultraviolet‐A Light Photodetector with Wide‐Range Photoresponse Based on ZnS/ZnO Biaxial Nanobelt

Enhancing electrochemical reaction sites in nickel-cobalt layered double hydroxides on zinc tin oxide nanowires: a hybrid material for an asymmetric supercapacitor device.

Polydopamine Spheres as Active Templates for Convenient Synthesis of Various Nanostructures

Ultrahigh external quantum efficiency from thin SnO2 nanowire ultraviolet photodetectors.