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1. MoS 2 Nanoflakes based Kilohertz Electrochemical Capacitors

   https://doi.org/10.1002/batt.202300363  

   Bal, Sourayan ; Baranwal, Rishav ; Lin, Xueyan ; Li, Wenyue ; Yang, Shize ; Islam, Nazifah ; Fan, Zhaoyang ( November 2023 , Batteries & Supercaps)

   An ultra‐fast electrochemical capacitor (EC) designed for efficient ripple current smoothing was fabricated using vertically oriented MoS₂(VOM) nanoflakes deposited on freestanding carbonized cellulose (CC) sheets as electrodes. The daily used cellulose tissue sheets were transformed into electrode scaffolds through a rapid pyrolysis process within a preheated furnace, on which VOM nanoflakes were formed in a conventional hydrothermal process. With these ~10 μm thick VOM‐CC electrodes, ultrafast ECs with tunable frequency response and specific capacitance density were fabricated. The ECs with a cell‐level areal capacitance density of 0.8 mF/cm²at 120 Hz were demonstrated for ripple current filtering from 60 Hz to 60 kHz. At a lower frequency response level, EC cell with a large capacitance density of 4.8 mF/cm²was also demonstrated. With the facile and easily scaled up process to producing the nanostructured electrode, the miniaturized VOM‐CC based ECs have the potential to substitute the bulky aluminum electrolytic capacitors for current smoothing and pulse power applications.

    

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2. ZIF-67-derived edge-oriented graphene clusters coupled with carbon nanotubes containing encapsulated Co nanoparticles for high-frequency electrochemical capacitors

   https://doi.org/10.1039/c9se00503j  

   Li, Wenyue ; Islam, Nazifah ; Azam, Sakibul ; Xu, Zhen ; Warzywoda, Juliusz ; Fan, Zhaoyang ( January 2019 , Sustainable Energy & Fuels)

   There is a strong interest in increasing the frequency response of electrochemical capacitors (ECs) from typically less than 1 Hz to the hundreds or the kilo Hz range, so that such high-frequency ECs (HF-ECs) could replace conventional capacitors for AC line-frequency filtering and other capacitor applications. The development of such HF-ECs is hindered by their typically low capacitance density and operation voltage. Herein, by treating ZIF-67 particulate films in CH 4 /H 2 plasma, edge-oriented graphene (EOG) formed around the carbonized ZIF-67 particulate skeleton, and this EOG was coupled with carbon nanotubes (CNTs) that were grown with the aid of Co catalyst nanoparticles, which were generated by reducing the Co 2+ ions associated with ZIF in the plasma. Used as electrodes, these EOG/CNT/carbonized ZIF-67 composites exhibited a large electrode areal capacitance of 1.0 mF cm −2 and an excellent frequency response of −84° phase angle at 120 Hz in aqueous electrolyte cells, whereas values of 0.67 mF cm −2 and −78° for the electrode areal capacitance and the phase angle at 120 Hz, respectively, were obtained in organic electrolyte cells with the operation voltage of 2.5 V. Using three pairs of electrodes stacked together, a single integrated cell operating at 7.5 V and having a characteristic frequency of ∼3.8 kHz at −45° phase angle, was demonstrated. These results suggest the potential to use this EOG/CNT/carbonized ZIF-67 composite structure for developing HF-ECs. 

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3. AC-Filtering Supercapacitors Based on Edge Oriented Vertical Graphene and Cross-Linked Carbon Nanofiber

   https://doi.org/10.3390/ma12040604  

   Li, Wenyue ; Islam, Nazifah ; Ren, Guofeng ; Li, Shiqi ; Fan, Zhaoyang ( February 2019 , Materials)

   There is strong interest in developing high-frequency (HF) supercapacitors or electrochemical capacitors (ECs), which can work at the hundreds to kilo hertz range for line-frequency alternating current (AC) filtering in the substitution of bulky aluminum electrolytic capacitors, with broad applications in the power and electronic fields. Although great progress has been achieved in the studies of electrode materials for ECs, most of them are not suitable to work in this high frequency range because of the slow electrochemical processes involved. Edge-oriented vertical graphene (VG) networks on 3D scaffolds have a unique structure that offers straightforward pore configuration, reasonable surface area, and high electronic conductivity, thus allowing the fabrication of HF-ECs. Comparatively, highly conductive freestanding cross-linked carbon nanofibers (CCNFs), derived from bacterial cellulose in a rapid plasma pyrolysis process, can also provide a large surface area but free of rate-limiting micropores, and are another good candidate for HF-ECs. In this mini review, advances in these fields are summarized, with emphasis on our recent contributions in the study of these materials and their electrochemical properties including preliminary demonstrations of HF-ECs for AC line filtering and pulse power storage applications. 

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4. A High‐Performance Symmetric Supercapacitor from Porous Activated Carbon under Compression

   https://doi.org/10.1002/ente.202100068  

   Sun, Wei ; Zhang, Yulin ; Yang, Fuqian ( April 2021 , Energy Technology)

   The realization of biomass‐derived supercapacitors of high performance is of practical importance for the manufacturing of supercapacitors from green and renewable sources. Herein, the feasibility of constructing high‐performance supercapacitors from potato‐derived activated carbon (AC) is demonstrated. The potato‐derived AC is produced from potato mash through hydrothermal treatment and high‐temperature activation with KOH as agent. The supercapacitors with aqueous electrolyte of 6 mKOH and a mass loading of 5 mg per electrode achieve a specific gravimetric capacitance of 333.7 F g⁻¹per electrode and a specific energy of 11.75 W h g⁻¹at a specific power of 197.6 W kg⁻¹at a current density of 0.4 A g⁻¹under a nominal compressive stress of 7.96 MPa. The supercapacitors with a mass loading of 10 mg per electrode achieve the maximum specific gravimetric capacitance of 340.6 F g⁻¹and a specific energy of 11.75 W h g⁻¹at a specific power of 194.2 W kg⁻¹at a current density of 0.4 A g⁻¹under a nominal compressive stress of 7.96 MPa. Increasing the compaction of electrode materials under compressive stress has the potential to increase the electrochemical performance of supercapacitors.

    

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5. Wood‐Inspired Morphologically Tunable Aligned Hydrogel for High‐Performance Flexible All‐Solid‐State Supercapacitors

   https://doi.org/10.1002/adfm.201909133  

   Zhao, Yusen ; Alsaid, Yousif ; Yao, Bowen ; Zhang, Yucheng ; Zhang, Bozhen ; Bhuskute, Neel ; Wu, Shuwang ; He, Ximin ( January 2020 , Advanced Functional Materials)

   Oriented microstructures are widely found in various biological systems for multiple functions. Such anisotropic structures provide low tortuosity and sufficient surface area, desirable for the design of high‐performance energy storage devices. Despite significant efforts to develop supercapacitors with aligned morphology, challenges remain due to the predefined pore sizes, limited mechanical flexibility, and low mass loading. Herein, a wood‐inspired flexible all‐solid‐state hydrogel supercapacitor is demonstrated by morphologically tuning the aligned hydrogel matrix toward high electrode‐materials loading and high areal capacitance. The highly aligned matrix exhibits broad morphological tunability (47–12 µm), mechanical flexibility (0°–180° bending), and uniform polypyrrole loading up to 7 mm thick matrix. After being assembled into a solid‐state supercapacitor, the areal capacitance reaches 831 mF cm⁻²for the 12 µm matrix, which is 259% times of the 47 µm matrix and 403% times of nonaligned matrix. The supercapacitor also exhibits a high energy density of 73.8 µWh cm⁻², power density of 4960 µW cm⁻², capacitance retention of 86.5% after 1000 cycles, and bending stability of 95% after 5000 cycles. The principle to structurally design the oriented matrices for high electrode material loading opens up the possibility for advanced energy storage applications.

    

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