Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries

Nickel foam-loaded Co-MOF@TiO2/MoS2 as electrode materials for dual-function devices for glucose detection and hydrogen evolution

Dual-functional nanomaterial electrodes have the capability to satisfy the requirements for both sweat analysis and the hydrogen evolution reaction (HER), thereby enabling the integration of electrochemical sensing and hydrogen production. In this study, ZIF-67 cubes are synthesized on nickel foam (NF), while TiO2 is obtained through an annealing process. Subsequently, the ZIF-67@TiO2/MoS2 nanocomposite is fabricated on nickel foam via a hydrothermal method. This composite material exhibits exceptional photocatalytic properties and is also suitable for the detection of glucose in sweat. The glucose detection range spans from 10 nM to 10 mM with a sensitivity of 7.24 μA mM-1 cm-2 for a signal-to-noise ratio of 3 and a detection limit of 0.43 μM. Moreover, when utilized as a hydrogen evolution electrode, this material demonstrates a current density of 10 mA cm-2 at an overpotential of 118 mV, with a Tafel slope of 73 mV/dec. The synthesis process is both straightforward and economical. This research introduces a novel concept for the design of multifunctional chemical sensors.

In Situ Fabrication of Hierarchical CuO@CoNi-LDH Composite Structures for High-Performance Supercapacitors

Layered double hydroxide (LDH) materials, despite their high theoretical capacity, exhibit significant performance degradation with increasing load due to their low conductivity. Simultaneously achieving both high capacity and high rate performance is challenging. Herein, we fabricated vertically aligned CuO nanowires in situ on the copper foam (CF) substrate by alkali-etching combined with the annealing process. Using this as a skeleton, electrochemical deposition technology was used to grow the amorphous α-phase CoNi-LDH nanosheets on its surface. Thanks to the high specific surface area of the CuO skeleton, ultrahigh loading (̃16.36 mg cm-2) was obtained in the fabricated CF/CuO@CoNi-LDH electrode with the cactus-like hierarchical structure, which enhanced the charge transfer and ion diffusion dynamics. The CF/CuO@CoNi-LDH electrode achieved a good combination of high areal capacitance (33.5 F cm-2) and high rate performance (61% capacitance retention as the current density increases 50 times). The assembled asymmetric supercapacitor device demonstrated a maximum potential window of 0-1.6 V and an energy density of 1.7 mWh cm-2 at a power density of 4 mW cm-2. This work provides a feasible strategy for the design and fabrication of high-mass-loading LDH composites for electrochemical energy storage applications.

Surface Engineering of Ni wires and Rapid Growth Strategy of Ni-MOF Synergistically Contribute to High-Performance Fiber-Shaped Aqueous Battery

The fiber-shaped aqueous battery (FSAB) has the advantages of flexibility, portability and safety making it promising for energy storage applications. In particular, FSABs based on metal wire current collectors with good electrical conductivity can provide excellent energy storage properties. However, the low adhesion caused by the smooth surface of the metal wire and the unavailability of many electrochemically active materials for use in FSAB is holding back their development. Herein, a substrate is effectively constructed for the strongly applicable growth of the active material via a Ni wire etching strategy. In addition, core-shell structured nanorod arrays consisting of NiCo₂ O₄ and Ni-metal-organic frameworks (MOFs) are constructed, where Ni-MOF can be obtained rapidly via β-Ni(OH)₂ intermediates. The NCO/NM-15 electrode obtained by structural regulation exhibits high capacity and outstanding cycling stability. De calculations further demonstrate that the formation of NiCo₂ O₄ and Ni-MOF heterostructures results in a significant increase in the Fermi level leading to more active internal electrons, which facilitates electron transfer in electrochemical reactions. An assembled FSAB device can provide an energy density of 158.33 µWh cm^-2 and the devices can provide power for a calculator and an electronic watch screen, demonstrating a wide application prospect in the field of energy storage.

Bi-functional 3D-NiCu-Double Hydroxide@Partially Etched 3D-NiCu Catalysts for Non-Enzymatic Glucose Detection and the Hydrogen Evolution Reaction

Hydrogen production, which is in the spotlight as a promising eco-friendly fuel, and the need for inexpensive and accurate electronic devices in the biochemistry field are important emerging technologies. However, the use of electrocatalytic devices based on expensive noble metal catalysts limits commercial applications. In recent years, to improve performance and reduce cost, electrocatalysts based on cheaper copper or nickel materials have been investigated for the non-enzymatic glucose oxidation reaction (GOR) and hydrogen evolution reaction (HER). In this study, we demonstrate a facile and easy electrochemical method of forming a cheap nickel copper double hydroxide (NiCu-DH) electrocatalyst deposited onto a three-dimensional (3D) CuNi current collector, which can effectively handle two different reactions due to its high activity for both the GOR and the HER. The as-prepared electrode has a structure comprising abundant 3D-interconnected porous dendritic walls for easy access of the electrolyte ions and highly conductive networks for fast electron transfer; additionally, it provides numerous electroactive sites. The synergistic combination of the dendritic 3D-CuNi with its abundant active sites and the self-made NiCu-DH with its excellent electrocatalytic activity toward the oxidation of glucose and HER enables use of the catalyst for both reactions. The as-prepared electrode as a glucose sensor exhibits an outstanding glucose detection limit value (0.4 μM) and a wide detection range (from 0.4 μM to 1.4 mM) with an excellent sensitivity of 1452.5 μA/cm2/mM. The electrode is independent of the oxygen content and free from chloride poisoning. Furthermore, the as-prepared electrode also requires a low overpotential of -180 mV versus reversible hydrogen electrode to yield a current density of 10 mA/cm2 with a Tafel slope of 73 mV/dec for the HER. Based on this performance, this work introduces a new paradigm for exploring cost-effective bi-functional catalysts for the GOR and HER.

A Better Zn-Ion Storage Device: Recent Progress for Zn-Ion Hybrid Supercapacitors

As a new generation of Zn-ion storage systems, Zn-ion hybrid supercapacitors (ZHSCs) garner tremendous interests recently from researchers due to the perfect integration of batteries and supercapacitors. ZHSCs have excellent integration of high energy density and power density, which seamlessly bridges the gap between batteries and supercapacitors, becoming one of the most viable future options for large-scale equipment and portable electronic devices. However, the currently reported two configurations of ZHSCs and corresponding energy storage mechanisms still lack systematic analyses. Herein, this review will be prudently organized from the perspectives of design strategies, electrode configurations, energy storage mechanisms, recent advances in electrode materials, electrolyte behaviors and further applications (micro or flexible devices) of ZHSCs. The synthesis processes and electrochemical properties of well-designed Zn anodes, capacitor-type electrodes and novel Zn-ion battery-type cathodes are comprehensively discussed. Finally, a brief summary and outlook for the further development of ZHSCs are presented as well. This review will provide timely access for researchers to the recent works regarding ZHSCs.

NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor

In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.