Microfluidic‐Architected Nanoarrays/Porous Core–Shell Fibers toward Robust Micro‐Energy‐Storage

Abstract

Methods enabling the controllable fabrication of orderly structural and active nanomaterials, along with high‐speed ionic pathways for charge migration and storage are highly fundamental in fiber‐shaped micro‐supercapacitors (MSCs). However, due to fiber‐electrodes with compact internal microstructure and less porosity, MSCs usually display a low energy density. Here, an innovative microfluidic strategy is proposed to design ordered porous and anisotropic core–shell fibers based on nickel oxide arrays/graphene nanomaterials. Owing to the homogeneous microchannels reaction, the graphene core maintains a uniformly anisotropic porous structure, and the nickel oxide shell keeps steadily vertically aligned nanosheets. The MSC presents an ultrahigh energy density (120.3 µWh cm−2) and large specific capacitance (605.9 mF cm−2). This higher performance originates from the microfluidic‐architected core–shell fiber with abundant ionic channels (plentiful micro‐/mesopores), large specific‐surface‐area (425.6 m2 g−1), higher electrical conductivity (176.6 S cm−1), and sufficient redox activity, facilitating ions with quicker diffusion and greater accumulation. Considering those outstanding properties, a wearable self‐powered system, converting and storing solar energy into electric energy, is designed to light up displays. This microfluidic strategy offers an effective way to design new structural materials, which will advance the development of next‐generation wearable/smart industries.

Anisotropic Boron–Carbon Hetero‐Nanosheets for Ultrahigh Energy Density Supercapacitors

“…The electrochemical performances of as‐prepared FSCs are evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) measurements. As shown in Figure 4 a (Supporting Information, Figures S21–S23), the CV profiles of bulk boron FSC exhibits the smallest integral area with a rectangular shape, indicating the lowest energy storage ability of electric double‐layer capacitance (EDLC) [37] . In contrast, the boron nanosheets FSC noteworthily shows a larger CV integral area, which implies that the gas‐phase exfoliated boron nanosheets with graphene‐like lamellar structure can effectively improve the EDLC.…”

Anisotropic Boron–Carbon Hetero‐Nanosheets for Ultrahigh Energy Density Supercapacitors

“…Figure 5 e shows the cycling stability of as‐prepared FSC by continually operating the charging/discharging processes. Satisfactorily, the ABCNs FSC maintains 94.1 % initial capacitance retention for 10 000 cycling tests without any obvious deterioration, indicating higher reversible ion absorption/desorption into/out of electrode‐electrolyte interfaces and good structural stability [37, 39] . The energy and power densities are more important parameters to evaluate the potentially actual application of FSC (Figure 4 f).…”

“…Thee lectrochemical performances of as-prepared FSCs are evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) measurements.A ss hown in Figure 4a (Supporting Information, Figures S21-S23), the CV profiles of bulk boron FSC exhibits the smallest integral area with ar ectangular shape,i ndicating the lowest energy storage ability of electric double-layer capacitance (EDLC). [37] In contrast, the boron nanosheets FSC noteworthily shows alarger CV integral area, which implies that the gas-phase exfoliated boron nanosheets with graphene-like lamellar structure can effectively improve the EDLC.M ore importantly,b yd esigning the anisotropic and ordered hetero-nanosheets,the ABCNs FSC displays the highest CV integral area, which reveals the greatest ion migration and charge-storage capabilities.T here are faint redox reactions of CV curve derived from the nitrogen activity in doped carbon nanosheets. [32] Additionally,t he ABCNs FSC also presents the longest charging/discharging times than those of bulk boron and boron nanosheets FSCs (Figure 4b;S upporting Information, Figures S24-S26), demonstrating the best interfacial charge transfer and electrochemical performance.T he detailed specific volumetric capacitances of the as-prepared FSCs at different current densities are shown in Figure 4c.Obviously,the ABCNs FSC performs the largest specific capacitance of 534.5 Fcm À3 at ac urrent density of 0.1 Acm À3 ,w hich makes as ignificant promotion compared with bulk boron and boron nanosheets of 174.2 and 310 Fcm À3 ,respectively.T he coulombic efficien- Figure S27.…”

Porous Organic Polymers as Promising Electrode Materials for Energy Storage Devices

“…With the fastbooming growth of microscale electronics, flexible, and wearable electronics, MSCs and fibershaped SCs (FSCs) have gained increasing attention. [67] For efficient MSCs and FSCs, it is highly desired to develop fibershaped electrodes with interconnected holey networks, ordered microporosity, larger specific surface area, and efficient fabrication methods, such as magnetothermal microfluidic method [68] and microliter dropletbased method. [105] Besides, efficient SCs require not only good electrode materials but also suitable electrolytes and optimal devices.…”

“…The MSC based on this core-shell fiber electrode exhibited high energy density (120.3 µWh cm −2 ) and large specific capacitance (605.9 mF cm −2 ), which was ascribed to the microfluidicarchitected core-shell fiber with abundant ionic channels (plentiful micro/mesopores), large specific surfacearea (425.6 m 2 g −1 ), higher electrical conductivity (176.6 S cm −1 ), and sufficient redox activity, facilitating ions with quicker diffusion and greater accumulation. [67] Wu et al prepared hierarchical carbon polyhedrons/holey graphene (CP/HG) core-shell microfibers by magnetothermal micro fluidic method ( Figure 5). The MSC based on P/HG afforded excellent energy density of 335.8 µWh cm −2 and high areal capacitance of 2760 mF cm −2 due to large specific surface area (569.43 m 2 g −1 ), open and welldefined ionic pathways, rich nitrogen activity of 5.6%, enhanced electrical conduc tivity of 13 290 S cm −1 , and good mechanical strength.…”