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Sintering performance at high temperatures is a serious issue for tetravalent metal pyrophosphate MP2O7 ceramics (M = Ti, Zr, Hf, Ge, Sn, etc.). Herein, we investigated the influence of high synthesis temperatures and amounts of ZrP2O7 precursors on the properties of ZrP2O7 ceramics. A ZrP2O7 powder was first synthesised via a solid-state reaction; this powder was used in the fabrication of the ZrP2O7 ceramic using a combination of two-step sintering and in situ bonding using MgO as the sintering aid. The phase composition and microstructure of the ZrP2O7 powder as well as the ZrP2O7 ceramic were studied by X-ray diffraction and scanning electron microscopy. The physical properties and room-temperature thermal conductivity of the ZrP2O7 ceramic were investigated. The ceramic exhibited high thermal stability at 1350 °C. This study indicates that the mechanical properties of the ZrP2O7 ceramic can be enhanced while maintaining their low thermal conductivity by sintering it at 1300 °C with the addition of an appropriate amount of the ZrP2O7 precursors to the ZrP2O7 powder.

Core-shell structured sulfur composite nanoparticles (NPs) and their various derivatives have been widely investigated as a promising cathode material for Li-S batteries (LSBs) thanks to their unique features in suppressing the lithium polysulfides shuttle effect, accommodating the sulfur electrode volume change, and providing abundant electrochemically active sites. The commonly used infiltration strategy falls short in producing a near ideal core-shell structure. Accordingly, the strategy of encapsulation, in which the prefabricated sulfur or sulfur precursor nanocore is encapsulated by a subsequently formed host shell has attracted broad interest, and this technique has significantly accelerated the LSB development. To advance the state of the art in producing encapsulated sulfur NPs, it becomes necessary to systematically survey the past relevant works and sum up research gaps. This review first takes an excursion to the infiltration strategy to highlight its limitations, followed by surveys on studies of synthesizing sulfur NPs, encapsulating sulfur NPs, and producing encapsulated sulfur NPs from metal sulfides. The strengths and weaknesses of each method, the resulted NPs, their electrochemical properties and the associated LSB performances are particularly emphasized. The rationales to design and the results of applying structural derivatives of the conventional core-shell configuration are then assessed. The encapsulated sulfur NPs applied in aqueous batteries are also discussed. This comprehensive review on sulfur encapsulation is concluded by a summary on further challenges and opportunities as well as our perspectives on possible future research directions, towards fundamental understanding and practical development of encapsulated sulfur NP-based LSB technology.

The practical application of lithium–sulfur batteries (LSBs) has been impeded by several chronic problems related to the insulating nature of sulfur and lithium sulfide, in addition to the dissolution and diffusion of lithium polysulfides. In view of these problems, a large variety of carbonaceous materials have been employed to enhance the electronic conductivity of the cathode and/or sequester lithium polysulfides within conductive matrixes. Although they may exhibit impressive electrochemical performance, the fabrication of most carbon materials involves costly precursors and complicated procedures. Waste paper—the main constituent of municipal waste—is composed of carbohydrates, and can be an ideal precursor for carbon materials. Herein, carbon microfiber meshes (CMFMs) obtained by the pyrolysis of common filter paper in argon (A-CMFM) or ammonia (N-CMFM) were used to form sulfur cathodes. Compared with LSBs based on A-CMFM, those based on N-CMFM demonstrated higher specific capacity and better rate capability, with a capacity of 650 mA h g−1 at 0.2 C and 550 mA h g−1 at 0.5 C. This was owing to the strong immobilization of lithium polysulfides resulting from the heteroatom doping and hydrophilicity of N-CMFM. The results indicate that cellulose paper-derived carbon is a promising candidate for application in high-performance LSBs.

With its unique features, lithium sulfide (Li2S) has been investigated as the cathode material for next-generation rechargeable batteries. Even though Li2S itself cannot solve all the problems faced by lithium-sulfur batteries (LSBs) and it may also introduce new issues, it does provide new opportunities. As the fully lithiated state of sulfur, Li2S offers the prospect of lithium-metal-free anodes and will also alleviate the volume expansion issues otherwise occurred in the sulfur cathode. Perhaps a most radical change when substituting sulfur with Li2S lies at the high-temperature process ability of the latter, thus opening new avenues to construct rationally designed electrodes. Despite sharing certain similarities with sulfur-based LSB, Li2S-based has its own opportunities and challenges in term of material synthesis, electrode fabrication, cell construction, and electrochemical behavior. To advance its state of the art, this review article discusses the current understandings on the initial Li2S activation process, which plays a crucial role in guiding Li2S nanostructure design and fabrication. With this leading thread, the article surveys impactful works on producing Li2S nanoparticles, encapsulating Li2S nanoparticles, simultaneously producing and encapsulating Li2S nanoparticles, and fabricating Li2S cathodes, followed by constructing lithium-metal-free LSBs. The pros and cons of different methods and the associated electrochemical behaviors are highlighted. Throughout, we call out the important research opportunities and challenges, both scattered out in the survey and aggregated in our conclusion perspective on future works, towards the fundamental understanding and practical development of Li2S-based LSBs.

Nano rotor is of great value in military and civilian applications. Due to its nano size, it works at an ultra-low Reynolds number and aerodynamic performance deteriorates dramatically. The bio-inspired nano rotor is carried out to improve the rotor propulsive performance. Unsteady vortex lattice method (UVLM) model is established fully considering the influence of induced drag and wake vortex distortion on aerodynamic forces. The aim is to quickly and accurately simulate the flow field around the bio-inspired nano rotor and to efficiently perform the aerodynamic calculation to optimise the design of the bio-inspired rotor. The rotor parameters and motion parameters such as aspect ratio, taper ratio and camber are studied using UVLM. It is found that the aerodynamic performance of the rotor increased with the aspect ratio. The quality factor changes parabolically with the taper ratio and camber, and there is an optimal value for the ratio and camber, respectively. The influences of pitching angle and frequency are investigated as well. Results show that the bio-inspired motion improves the propulsion performance of nano rotor.

A compact two-mode switch with broad bandwidth is presented in this paper. The design of the proposed switch is based on a symmetric Y-junction which is composed of a silicon multimode straight waveguide, a silicon taper, and two symmetrical graphene–silicon s-bend waveguides. When voltage signals are applied to efficiently change the chemical potential of the embedded graphene, input modes can be separated, converted, and routed to the output ports flexibly at a high speed. Calculations indicate that, the crosstalk of the presented switch with an area of ∼ 65 × ∼ 1. 7 μ m 2 is less than −12.10 dB over a 95 nm band, the switching voltage for shifting the chemical potential is 4.18 V, the corresponding energy consumption is less than 2.90 pJ/bit, and the calculated 3-dB bandwidth larger than 47.94 GHz can be obtained.

In this paper, an electro-optic majority voting circuit based on graphene-silicon nitride waveguides is proposed and numerically investigated. The proposed circuit is composed of 2×1 multimode interference combiners and Mach-Zehnder interferometers where graphene-silicon nitride waveguides are designed for phase shifters. By adjusting graphene’s chemical potential electrically, the proposed graphene-silicon nitride waveguide has a large variation in the real part of the effective refractive index so that a relatively compact and low-energy-consumption majority voting circuit can be realized. Simulation results show that as graphene’s chemical potential is increased from 0.50 to 0.60 eV at an operating wavelength of 1550 nm, the designed graphene-silicon nitride waveguide with a 5 nm spacer of TiO2can have 0.34 pJ/bit energy consumption andVπ • Lπ of 43.15 V•μm.The corresponding electro-optic majority voting circuit has an extinction ratio larger than 20.11 dB.

In this paper, a two-mode (de)multiplexer utilizing the coupling between tapered waveguides and a wide multimode waveguide is designed and experimentally demonstrated. The tapered waveguides are composed of a reverse-tapered waveguide and a narrow tapered waveguide. The proposed mode (de)multiplexer is fabricated on silicon-on-insulator (SOI) wafer in a commercial 0.18-μm CMOS-compatible process. The qualitative functionality of the device is mainly determined by the width of the large end of the reverse-tapered waveguide. Experimental results show that the demultiplexing crosstalk of a pair of tapered-coupler-based two-mode (de)multiplexers is lower than −13.5 dB within a bandwidth from 1528 nm to 1570 nm and less than −16.6 dB from 1540 nm to 1560 nm.

Conductive and porous carbon plays critical roles as electrode material for electrochemical energy storage devices, including supercapacitors. Using commonly available biomass cellulous fibers as the raw material to produce porous carbon is a promising approach to achieve high-performance and low-cost electrodes. Herein, carbon microfiber (CMF) membranes were prepared via a direct carbonization method using cotton fiber meshes as precursors. The nitrogen doping content, carbon surface area and pore density could be well adjusted by the carbonization atmosphere and temperature. With CMF membranes as freestanding electrodes in supercapacitors, remarkable electrochemical performances were demonstrated. In particular, the CMF membrane obtained at 800 °C in ammonia (CMFs-800) can achieve a high capacitance of 172 F g-1 at the current density of 0.1 A g−1, meanwhile it shows excellent rate capability and superior cycling stability. This study indicates that the pyrolyzed cotton mesh, due to its large pore density, high specific surface area, and heteroatom doping, has potential to be used as cost-effective electrode for supercapacitors.

Dendrimers, with their unique structure and polyfunctionality, have shown excellent performance in many biomedicinal applications, such as drug carriers and gene transfection. In this study, titanium dioxide (TiO2) films with four generations (G1, G2, G3, G4) of amino-terminated dendrimers were prepared in situ using a simple iterative Michael addition and aminolysis reaction for generational growth. The TiO2 films with different generations of dendrimers were characterized using X-ray diffraction, water contact angle measurements, and scanning electron microscopy. The chemical compositions of these films were confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Blood compatibility was evaluated using platelet adhesion and activation assays utilizing platelet-rich plasma. The results indicated that the dendrimers immobilized on the surface of the TiO2 films effectively reduced platelet adhesion and aggregation. Endothelial cell culturing on the dendrimer-immobilized surfaces showed that the amino-terminated dendrimers exhibited a certain degree of cytotoxicity due to the positive charges of the amino groups. These results indicated that amino-terminated dendrimers immobilized on TiO2 films provided numerous functional groups for the future immobilization of specific biological molecules and may be used for manufacturing future blood-contacting implants.

Polysulfide shuttle effect, causing extremely low Coulombic efficiency and cycling stability, is one of the toughest challenges hindering the development of practical lithium sulfur batteries (LSBs). Introducing catalytic nanostructures to stabilize the otherwise soluble polysulfides and promote their conversion to solids has been proved to be an effective strategy in attacking this problem, but the heavy mass of catalysts often results in a low specific energy of the whole electrode. Herein, by designing and synthesizing a free-standing edge-oriented NiCo 2 S 4 /vertical graphene functionalized carbon nanofiber (NCS/EOG/CNF) thin film as a catalytic overlayer incorporated in the sulfur cathode, the polysulfide shuttle effect is largely alleviated, revealed by the enhanced electrochemical performance measurements and the catalytic function demonstration. Different from other reports, the NiCo 2 S 4 nanosheets synthesized here have a 3-D edge-oriented structure with fully exposed edges and easily accessible in-plane surfaces, thus providing a high density of active sites even with a small mass. The EOG/CNF scaffold further renders the high conductivity in the catalytic structure. Combined, this novel structure, with high sulfur loading and high sulfur fraction, leads to high-performance sulfur cathodes toward a practical LSB technology.

High-quality perovskite films are essential for high-performance perovskite solar cells (PSCs). Here we first proposed a polar anti-solvent technology of sec-pentyl alcohol (2-PA) for the fabrication of perovskite films. Our investigations have proven that 2-PA, as a better anti-solvent than conventional those with non- and high-polarity, enables the fabrication of uniform and dense perovskite films with mirror-like surface and film-through large grains. We found that moderate polar solvent more advantageously influences the crystallinity and morphology of perovskite films by extracting thoroughly the residual solvent and promoting a more complete and fast transformation from the lead polyhalide framework to the targeted perovskite film. By our proposed way, the best performing PSCs based on methylammonium lead iodide showed a power conversion efficiency (PCE) of over 17% under AM 1.5G illumination with high reproducibility and no photocurrent hysteresis. Our investigation indicates that sec-pentyl alcohol as anti-solvent could be an universal method for the preparation of hybrid organic-inorganic perovskite film.

Highly insulating nature of sulfur species and the shuttling effects caused by soluble lithium polysulfides have been blamed for hindering the development of lithium–sulfur (Li–S) batteries. A variety of carbonaceous materials have been investigated to ameliorate these problems by providing a conductive matrix with physical trapping and chemical binding capabilities, but inevitably resulted in typically low sulfur content in the cathode and hence low gross specific energy when considering all the active and inactive masses. A highly conductive and crosslinked matrix with superior trapping and binding capability to sulfur species but a very low mass density is essential. Herein, crosslinked carbon nanofiber aerogel (CNFA) with extremely low density, attained from pyrolysis of bacterial cellulose (BC) aerogel, was studied for sulfur cathodes. With its unique combination of several merits, in particular the capability of strong absorption of catholyte, CNFA based sulfur electrodes exhibit outstanding performance. With 75% sulfur content of the gross cathode mass, cells demonstrated an initial capacity of 1360 mA h g−1 at 0.2 C, and exhibited excellent cycling stability with 76% of the initial capacity retained after 200 cycles.

There are great needs in developing compact-size kilohertz (kHz) high-frequency (HF) electrochemical capacitors (ECs) for ripple current filtering and environmental vibration energy harvesting. However, the previously demonstrated electrodes are generally limited to a very small areal capacitance density at 120 Hz due to sub-μm thick electrode used for meeting frequency requirement, which renders them unsuitable for practical ECs. Here, using crosslinked carbon nanofiber aerogel, derived from rapid microwave plasma pyrolysis of bacterial cellulose that was synthesized in a fermentation process, we demonstrated kHz HF-ECs with areal capacitance density as high as 4.5 mF cm −2 at 120 Hz in an aqueous electrolyte. The cruciality of plasma pyrolysis on high frequency response of the derived carbon nanofiber aerogel was discussed. The electrode performance in an organic electrolyte was further studied for operation in a large potential window of more than 3 V. Using such kHz HF-ECs, we further demonstrated their applications in rapid pulse energy storage for vibrational energy harvesting, as well as in ripple current filtering for AC/DC conversion. The promising results suggest this technology has great potential for developing practical compact HF-ECs in substitution of electrolytic capacitors for several crucial applications.

A significantly improved conductive matrix design for the sulfur electrode is essential to solve several problems related to sulfur electrochemistry toward the development of practical lithium–sulfur batteries (LSBs). Great progress has been made by using a variety of carbon-based nanostructures for physically and chemically confining soluble polysulfides as well as providing conductive paths. However, most of these electrode designs have a low sulfur content or a low sulfur loading, leading to a low specific capacity or low areal capacity at the electrode level. Herein, intrinsically N- and O-doped carbon nanoribbon (CNR) aerogels, obtained by pyrolysis of bacterial cellulose (BC) aerogels, were employed to form gel-based sulfur cathodes, simultaneously achieving both a high sulfur content and a high sulfur loading. With a sulfur loading of 6.4 mg cm−2 and a sulfur content of 90% at the whole electrode (including the current collector) level, a capacity as high as 943 mA h g−1 was achieved, which corresponds to an areal capacity of 5.9 mA h cm−2. The outstanding cell performance is attributed to the gel based cathode structure, which can strongly hold a large amount of the catholyte and relieve the shuttle effect of lithium polysulfides.

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.

To alleviate the polysulfides shuttle effect in lithium–sulfur batteries (LSBs), the use of a functionalized carbon matrix with a polar surface has been widely reported to chemically bind the soluble polysulfides. However, whether and how such a polar carbon surface affects the overall cathode performance, particularly the initial discharge corresponding to the reduction of cyclooctasulfur (S8), has not caught enough attention. By combining polar and nonpolar carbon matrix surfaces in different configurations through sandwiching sulfur species between two carbon matrix membranes, we found cells with dramatically different performance. The discharge process at different states, particularly the charge-transfer resistances corresponding to nonpolar S8 and polar polysulfide intermediates and the final Li2S, were investigated. The experimental results, further supported by first-principles density functional theory calculations, indicate that the adsorption energy and barrier for electron transfer together af...

An hierarchical porous carbon nanostructure with intrinsic O- and N-dopants and an ultrahigh specific surface area of 1500 m2 g−1 is reported towards the goal of designing and achieving a better sulfur electrode for lithium–sulfur batteries (LSBs) that can provide both large sulfur loading and large sulfur content and are based on a facile fabrication process. This nanostructure was derived from crude soybeans in a facile pyrolysis process. Using it as a sulfur host, the S/C active composite with 80% sulfur content was made. Cells with different sulfur loadings were investigated and were found to demonstrate large capacity, high coulombic and energy efficiencies, and high cycling stability. In particular, for a sulfur loading of 5.5 mg cm−2 and a sulfur content of 80%, cells displayed a specific capacity of ca. 950 mA h g−1, which corresponds to an areal capacity of 5.2 mA h cm−2. Such a performance moves LSB technology closer to practical applications.

Lithium sulfide (Li2S) cathode can pair with metallic-Li-free high-capacity anodes to avoid the notorious lithium dendrite growth and resulting serious safety hazards. However, its high sensitivity to moisture and oxygen makes time-consuming slurry-casting process not appropriate for Li2S cathode production. Herein, interconnected carbon nanofibers (CNFs) and porous carbon (PC) inlaid with Li2S (Li2S@PC@CNF) has been fabricated via a carbothermal reduction strategy by selecting a cost-effective and environmentally friendly precursor, i.e., bacterial cellulose (BC) hydrogel filled with glucose and Li2SO4. Self-supporting Li2S@PC@CNF could be directly applied as the cathode, thereby detouring the routinely needed slurry-casting procedure. CNFs serve as a network for electron transport and meanwhile a skeleton to support the free-standing Li2S@PC@CNF electrode, while PC seamlessly connects CNFs due to the initial hydrogen bonding between glucose and cellulose, providing physical confinement for lithium polysulfides and large interface area for electrochemical reaction. Thereby, due to its unique ferroconcrete-like architecture, Li2S@PC@CNF based LSBs delivers a high initial specific capacity of 700 mA h g−1 with 500 mA h g−1 retained after 400 cycles, and presents promising rate capability of 450 mA h g−1 at 2 C.

A graphene-based plasmonic half-adder using cascaded microring resonators is proposed and theoretically investigated. Two electrical signals are applied to modulate microring resonators to adjust the chemical potentials of graphene, resulting in a change in the modal effective index so that the logic function of the half-adder can be performed. Performance of the designed graphene-based plasmonic half-adder is analyzed by using COMSOL and CST. Calculation results show that the maximum crosstalk of the half-adder at an operating frequency of 30 THz is -10.23 dB when input logic states are '00', '01', '10', and '11'.

An integrated flexible-grid 1×2 wavelength-selective switch based on reconfigurable add-drop silicon microring resonators using strip waveguides is designed and experimentally demonstrated. By flexibly tuning the resonance of microring resonators and path phase differences via the thermo-optic effect, the transmission spectra with adjustable bandwidths can be formed as desired at the output ports. Our experimental results reveal that the fabricated flexible-grid 1×2 wavelength-selective switch provides crosstalk lower than -10.39 dB. The 3-dB bandwidth varies from 0.38 nm to 1 nm, the in-band ripple is less than 0.52 dB, and the response time is about 17.6 μs.