The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Design and fabrication of electrochemical energy storage systems with both high energy and power densities as well as long cycling life is of great importance. As one of these systems, Battery-supercapacitor hybrid device (BSH) is typically constructed with a high-capacity battery-type electrode and a high-rate capacitive electrode, which has attracted enormous attention due to its potential applications in future electric vehicles, smart electric grids, and even miniaturized electronic/optoelectronic devices, etc. With proper design, BSH will provide unique advantages such as high performance, cheapness, safety, and environmental friendliness. This review first addresses the fundamental scientific principle, structure, and possible classification of BSHs, and then reviews the recent advances on various existing and emerging BSHs such as Li-/Na-ion BSHs, acidic/alkaline BSHs, BSH with redox electrolytes, and BSH with pseudocapacitive electrode, with the focus on materials and electrochemical performances. Furthermore, recent progresses in BSH devices with specific functionalities of flexibility and transparency, etc. will be highlighted. Finally, the future developing trends and directions as well as the challenges will also be discussed; especially, two conceptual BSHs with aqueous high voltage window and integrated 3D electrode/electrolyte architecture will be proposed.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201600539

Battery-Supercapacitor Hybrid Devices: Recent Progress and Future Prospects.

Mixed metal sulfides (MMSs) have attracted increased attention as promising electrode materials for electrochemical energy storage and conversion systems including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), hybrid supercapacitors (HSCs), metal–air batteries (MABs), and water splitting. Compared with monometal sulfides, MMSs exhibit greatly enhanced electrochemical performance, which is largely originated from their higher electronic conductivity and richer redox reactions. In this review, recent progresses in the rational design and synthesis of diverse MMS-based micro/nanostructures with controlled morphologies, sizes, and compositions for LIBs, SIBs, HSCs, MABs, and water splitting are summarized. In particular, nanostructuring, synthesis of nanocomposites with carbonaceous materials and fabrication of 3D MMS-based electrodes are demonstrated to be three effective approaches for improving the electrochemical performance of MMS-based electrode materials. Furthermore, some potential challenges as well as prospects are discussed to further advance the development of MMS-based electrode materials for next-generation electrochemical energy storage and conversion systems.

Mixed Metal Sulfides for Electrochemical Energy Storage and Conversion

In this paper, a hierarchical NiCo2S4@polypyrrole core–shell heterostructure nanotube array on Ni foam (NiCo2S4@PPy/NF) was successfully developed as a bind-free electrode for supercapacitors. NiCo2S4@PPy-50/NF obtained under 50 s PPy electrodeposition shows a low charge-transfer resistance (0.31 Ω) and a high area specific capacitance of 9.781 F/cm2 at a current density of 5 mA/cm2, which is two times higher than that of pristine NiCo2S4/NF (4.255 F/cm2). Furthermore, an asymmetric supercapacitor was assembled using NiCo2S4@PPy-50/NF as positive electrode and activated carbon (AC) as negative electrode. The resulting NiCo2S4@PPy-50/NF//AC device exhibits a high energy density of 34.62 Wh/kg at a power density of 120.19 W/kg with good cycling performance (80.64% of the initial capacitance retention at 50 mA/cm2 over 2500 cycles). The superior electrochemical performance can be attributed to the combined contribution of both component and unique core–shell heterostructure. The results demonstrate that the ...

Construction of a Hierarchical NiCo2S4@PPy Core–Shell Heterostructure Nanotube Array on Ni Foam for a High-Performance Asymmetric Supercapacitor

The metal oxides/graphene composites are one of the most promising supercapacitors (SCs) electrode materials. However, rational synthesis of such electrode materials with controllable conductivity and electrochemical activity is the topical challenge for high-performance SCs. Here, the Co_3O_4/graphene composite is taken as a typical example and develops a novel/universal one-step laser irradiation method that overcomes all these challenges and obtains the oxygen-vacancy abundant ultrafine Co_3O_4 nanoparticles/graphene (UCNG) composites with high SCs performance. First-principles calculations show that the surface oxygen vacancies can facilitate the electrochemical charge transfer by creating midgap electronic states. The specific capacitance of the UCNG electrode reaches 978.1 F g^(−1) (135.8 mA h g^(−1)) at the current densities of 1 A g^(−1) and retains a high capacitance retention of 916.5 F g^(−1) (127.3 mA h g^(−1)) even at current density up to 10 A g^(−1), showing remarkable rate capability (more than 93.7% capacitance retention). Additionally, 99.3% of the initial capacitance is maintained after consecutive 20 000 cycles, demonstrating enhanced cycling stability. Moreover, this proposed laser-assisted growth strategy is demonstrated to be universal for other metal oxide/graphene composites with tuned electrical conductivity and electrochemical activity.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201700659

Oxygen-Vacancy Abundant Ultrafine Co3O4/Graphene Composites for High-Rate Supercapacitor Electrodes.

The applications of traditional asymmetric supercapacitors are restricted due to the low specific capacitance of carbon negative materials. The rational design of positive and negative electrodes that afford high-performance asymmetric devices is particularly important. In this paper, we fabricate a cost-effective, environmental-friendly aqueous asymmetric supercapacitor by using CuCo2O4/CuO nanowire arrays as the positive electrode and RGO/Fe2O3 composites as the negative electrode. The assembled device exhibits a high energy density of 33.0 W h kg−1 at a power density of 200 W kg−1, and it still operates at a high power density of 8.0 kW kg−1 with an energy density of 9.1 W h kg−1. The current strategy will provide a fresh route for the design and fabrication of novel asymmetric supercapacitors with high energy density and high power density.

Hydrothermal synthesis of CuCo2O4/CuO nanowire arrays and RGO/Fe2O3 composites for high-performance aqueous asymmetric supercapacitors

A hierarchical NiCo2S4@Ni3V2O8 core/shell hybrid was in situ grown on nickel foam through a facile hydrothermal process combined with a simple co-precipitation method. Further characterization shows that the hybrid consists of highly conductive NiCo2S4 as the core and uniformly distributed Ni3V2O8 nanoparticles as the shell. When used as the binder-free electrode, the hybrid material takes advantage of both components and exhibits excellent electrochemical activity, demonstrating a higher specific capacity of 512 C g−1 at a current density of 1 A g−1 and a better rate capability of 396 C g−1 at 10 A g−1. The enhanced pseudocapacitive performance of the NiCo2S4@Ni3V2O8 hybrid is mainly attributed to its unique core/shell structure, which provides fast ion and electron transport. Finally, a NiCo2S4@Ni3V2O8//activated carbon asymmetric supercapacitor is successfully assembled and it can deliver a maximum energy density of 42.7 W h kg−1 at a power density of 200 W kg−1, making it a promising candidate for superior electrodes for supercapacitor applications.

In situ growth of NiCo2S4@Ni3V2O8 on Ni foam as a binder-free electrode for asymmetric supercapacitors

High rate capability of mesoporous NiWO4–CoWO4 nanocomposite as a positive material for hybrid supercapacitor

Immunoassay as a rapid and convenient method for detecting a variety of targets has attracted tremendous interest with its high specificity and sensitivity. Among the commonly used immunoassays, enzyme‐linked immunosorbent assay has been widely used as a gold standard method in various fields that consists of two main components including a recognition element and an enzyme label. With the rapid advances in nanotechnology, nanobodies and nanozymes enable immunoassays with enhanced specificity and sensitivity compared with conventional antibodies and natural enzymes. This review is focused on the applications of nanobodies and nanozymes in immunoassays. Nanobodies advantage lies in their small size, high specificity, mass expression, and high stability. Nanozymes with peroxidase, phosphatase, and oxidase activities and their applications in immunoassays are highlighted and discussed in detail. In addition, the challenges and outlooks in terms of the use of nanobodies and the development of novel nanozymes in practical applications are discussed.

Yidan Wang

Papers

Hydrothermal synthesis of CuCo2O4/CuO nanowire arrays and RGO/Fe2O3 composites for high-performance aqueous asymmetric supercapacitors

In situ growth of NiCo2S4@Ni3V2O8 on Ni foam as a binder-free electrode for asymmetric supercapacitors

High rate capability of mesoporous NiWO4–CoWO4 nanocomposite as a positive material for hybrid supercapacitor

Nanobody and Nanozyme‐Enabled Immunoassays with Enhanced Specificity and Sensitivity

Facilely synthesis of 3D CuxO–Cu nanostructures as binder-free electrode for supercapacitors