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Nowadays, SiO2 based material is one of the widest used materials in optical, microelectromechanical system, aerospace and some other industries. In practical application, SiO2 based materials are required to be joined with themselves or other heterogeneous materials to assemble products with various functions. And the joining quality directly affects the mechanical performances and functional properties of assembled products. Though many researchers studied different joining technologies, explored the microstructure of joining interface and tested after-joining properties, a review that summarizes the recent cutting-edge researches and development tendency of joining technologies for SiO2 based ceramics is still absent. Therefore, according to different applications and requirements, this review summarizes the widely used joining technologies and discusses corresponding joining mechanisms, current research progress and suitable applications. Due to the wide applications in specific industry, laser welding, anodic bonding and wafer bonding are discussed in detail. Further, brazing, the widest used method in SiO2 joining, has been elaborated deeply in its wetting mechanism, residual stress control, interfacial microstructure and mechanical performance aspects. In the end, this review proposed the future development trends of SiO2 ceramics joining, aiming at offering a full-view of potential improvements in SiO2 ceramic joining technologies.

Surface structure of C/C composites has been regulated through electrochemical corrosion at room temperature to modify the residual stress and improve the joining strength when brazed to Nb. The unique crevice corrosion in C/C composites is investigated to reveal the change of corrosion depth and fiber size. The interlacing zone of carbon fiber reinforced brazing alloy replaces the reaction layer in the original joint. Joining area is increased dramatically and the continuous crack will be hindered. The interlacing zone eliminates the stress concentration and relieves the residual stress through reducing the property mismatch. All advantages contribute to the joining quality of C/C Nb. Shear strength of C/C Nb joint with 80 μm depth reached 37.7 MPa, which was 1.2 times higher than that of original joint. Surface structure design of C/C composites not only expands the application in structure component, but also exhibits the promising application in energy field.

C/C composites are brazed to GH3536 superalloy with BNi2+Ni interlayer based on in-situ alloying conception. Through the liquid-solid reaction and diffusion, the original microstructure of C/C/Cr23C6/Ni(s,s)+Cr3Ni2+Ni-Si + Cr9Mo21Ni20/GH3536 is transformed into C/C/Cr7C3/Ni(s,s)/GH3536. High Ni (s,s) content increases the deformability and uniforms the composition of joint. Residual stress caused by the property mismatch is modified through deformability increase. Both increases the joining strength consequently. The phase of low melting point diffuses into Ni interlayer, which improves the high temperature performance efficiently. The optimal range of Ni interlayer is from 150 μm to 300 μm. The highest shear strength of joint reaches 32.6 MPa and 20.1 MPa at room temperature and 1000 °C, respectively.

Electrocatalytic water splitting driven by electrocatalysts is recognized as a promising strategy to generate clean hydrogen fuel. Searching and constructing high-efficient and low-cost electrocatalysts is vital in the practical applications of electrocatalytic water splitting. Although transition metal-based materials have been considered as promising electrocatalysts, the satisfactory activities are usually not built on the bulk materials, but strongly relying on elaborately designing these electrocatalysts. Herein, the recent theoretical and experimental progress on modification strategies to improve the intrinsic activities is summarized, especially including element doping, phase engineering, structure cooperation, interface engineering, vacancy engineering, strain engineering and self-functionalization. Finally, the future opportunities and challenges on these modification strategies are also proposed. Overall, it is anticipated that these modification strategies offer some new understandings on rationally constructing non-noble electrocatalysts for efficient electrocatalytic water splitting.

Nano tungsten reinforced carbon cloth (W-Cc) has been fabricated successfully to improve the joining quality of C/SiC-Nb joints as interlayer. Prominent advantage of this interlayer was to disperse high content of W and carbon fibers homogenously. They would maintain their low CTE during metallurgy reaction with Ti. It could relieve the residual stress caused by properties mismatch effectively. Another contribution to joining strength was to modify the fracture path. The shear strength of joints reinforced with W-Cc was increased to 131.8 MPa, which was 57 % higher than that of the original joints.

Element doping is a general and effective approach to modify the electrocatalytic performances, but the low intrinsic activity in each electroactive site still limits the further improvements. Herein, we provide an effective strategy by simultaneously introducing P doping and Se vacancies to enhance the intrinsic activities in NiSe2 nanosheet arrays (A-NiSe2|P) through Ar plasma treatment. Owing to the increased active sites and enhanced electrical conductivity, the resulted A-NiSe2|P shows the enhanced hydrogen evolution performances. Theoretical calculations reveal that introduction of Se vacancies plays a significant role in lowering the adsorption free energy of H* in Ni, Se and P sites, leading to promoted intrinsic activities in A-NiSe2|P. Further, A-NiSe2|P as bifunctional electrocatalysts only needs 1.62 V to reach 10 mA cm−2 for overall water splitting. Our study and understanding of A-NiSe2|P may highlight the importance of element doping and vacancies in enhancing the catalytic activities in overall water splitting.

Exploring earth-abundant and effective electrode material for electrocatalytic water splitting is vital for energy conversion devices. In this study, S doped NiCoP nanosheet arrays with rich P vacancies (A-NiCoP|S) are developed through plasma treatment. Starting from growing NiCoP through hydrothermal and phosphating processes, S dopant and P vacancy are simultaneously introduced into NiCoP by Ar plasma treatment. The synergic effect of S dopant and P vacancy leads to increased exposed active sites, optimized surface chemical states and improved electrical conductivity. Consequently, A-NiCoP|S shows superior activities with low overpotentials of 88 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) in 1 M KOH, as well as a low Tafel slope of 73.7 mV dec−1. Further, theoretical calculations demonstrate that the synergistic effects of S dopant and P vacancy can modify the electronic structure and lower free energy of hydrogen adsorption in NiCoP, thus promoting the reaction mechanism. Moreover, the water-splitting configuration by A-NiCoP|S only needs 1.60 V to attain 10 mA cm−2.

Constructing well-defined interfaces is vital to improve the electrocatalytic properties, but the studies on transition-metal-interface electrocatalysts with rich vacancies are rarely reported. Here, rich P vacancies to modulate Ni2P/Cu3P interfaced nanosheets for overall water splitting is demonstrated. We conduct a series of experimental parameters to adjust the nanostructures of Ni2P/Cu3P, and to get insight into the synergistic effects of interfaces and P vacancies on the catalytic activities. Notably, Ni2P/Cu3P with rich P vacancies shows the lowest overpotential requirements of 88 and 262 mV at 10 mA cm−2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The good activity is ascribed to abundant electroactive sites, electric field effect at the interfaces and tuning the electron structure by P vacancies. In addition, as bifunctional electrode, Ni2P/Cu3P with rich P vacancies allows for a low water-splitting voltage of 1.60 V at 10 mA cm−2. This work may open up a new route for efficient electrocatalysts through the synergistic effects of interfaces and vacancies.

Transition metal oxides show great potential as electrocatalysts, owing to the low cost and rich chemical states. However, the limited surface areas, low intrinsic activity and poor hydrogen evolution reaction (HER) activity greatly restrict the application for overall water splitting. Herein, we have constructed S doped NiCo2O4 nanosheet arrays by Ar plasma (Ar-NiCo2O4|S) to enhance active sites and boost catalytic kinetics. Consequently, the Ar-NiCo2O4|S shows the improved performances for HER and oxygen evolution reaction (OER). Further, as bifunctional electrocatalysts, Ar-NiCo2O4|S exhibit a voltage of 1.63 V at 10 mA cm−2, as well as good stability.

Owing to low-cost and 3d electronic configurations, Co3O4 material is considered as promising candidate for oxygen evolution reaction (OER) electrocatalyst, but the intrinsically low conductivity and limited active site exposure greatly limit the electrocatalytic performances, Herein, we successfully achieve modulation of Co3O4 arrays by Mn and S dual-doping for OER. Results demonstrate that Mn doping modifies the electronic structure of Co center to boost the intrinsic activity of active site in Co3O4, while inducing S in Co3O4 increases the electrical conductivity and provides ample S sites for proton adsorption. In addition, Mn and S dual-doping effectively increase the proportion of Co3+, resulting in facilitating the four-electron transfer and thus higher electrochemical activities. Consequently, the optimal Mn and S dual-doping Co3O4 presents low overpotentials of 330, 407 and 460 mV at 10, 100 and 300 mA cm−2 for OER, as well as a low Tafel slope of 68 mV dec−1 and a good durability after 20 h. Current work highlights a feasible strategy to design electrocatalysts via dual-doping and maximizing the high-valence transition metal ions.

Brazing SiO2f/SiO2 composites is always associated with the problem of poor wettability, and directly brazing SiO2f/SiO2 to Nb with AgCuTi cannot obtain the high strength joints. To overcome the problem, strong binding Si layer was synthesized on SiO2f/SiO2 surface by magnesiothermic reduction method. Results show that the content of Si raised to twice higher than original composites. The contact angle of AgCuTi on SiO2f/SiO2 composites was decreased from 95.9° to 34.7° via reducing SiO2 into Si. Due to the reaction of Si and Mg, SiO2 matrix were corroded to some extent inducing the zigzag reaction layer in the joints. With the increasing of Si content, O contained compounds in reaction layer were replaced by Ti-Si phase. And low thermal expansion Ti5Si3 particles would disperse near the reaction layer to maintain the stability of reaction layer. The highest shear strength reached 38.3 MPa with 4 h reducing treatment.

Titanium dioxide (TiO2) is an excellent photocatalyst and transparent conducting oxide. It has two major crystal structures: rutile and anatase. Anatase TiO2 is valuable from an industrial point of view because it typically displays better photocatalytic and electronic transport properties than rutile TiO2. To further extract the functional properties of TiO2, understanding the correlation between the electronic structure and the crystal structure is essential. Because the electronic structure strongly depends on the crystal structure, introducing lattice distortion to rutile TiO2 should effectively modulate its electronic structure. Here, we show that Nb-doped rutile TiO2 epitaxial films on ([Formula: see text]) α-Al2O3 substrates exhibit anatase-like optoelectronic properties due to orthorhombic lattice distortions and experimentally observe the change in the electronic structure. Reducing the film thickness increases the orthorhombic distortion ratio ( b/ a) up to 3.4%. As b/ a increases, the carrier effective mass decreases from 35 to 3 m0 ( m0: electron mass) and the optical bandgap significantly increases. The present observations provide insight into regulating the TiO2 physical properties and should be beneficial for designing TiO2-based photocatalysts and transparent conducting electrodes.

As a next-generation anode material for lithium batteries, Li metal anode suffers from inherent drawbacks such as infinite volume expansion and uneven Li plating/stripping. Herein, we propose a lightweight lithiophilic Prussian blue analogue (PBA) with honeycomb-like structure on Cu foam by self-assembly method to address these issues. The unique honeycomb-like architecture could provide enlarged surface areas and abundant deposition sites for homogenizing Li+ flux during Li plating. Consequently, the elaborate PBA-decorated Cu foam current collector enables long-term (1800 h) reversible plating/stripping behavior and an observably improved Coulombic efficiency (98.3% after 350 cycles). The concept of the direct self-assembly synthesis method on metal foam provides new insights into the design of a lightweight 3-dimensional current collector for Li metal anode.

A negative expansion LiAlSiO4 (LAS) network has been developed for C/C–Nb joints to modify the residual stress. LAS network was sintered elaborately obtaining high strut strength and smooth surface. AgCuTi brazing alloy had good wettability on LAS and infiltrated into network with faultless interfacial joining. The effect of stiff network structure on the stress dispersion of composite joints was investigated innovatively. The shear strength of joints modified with LAS network raised to 45.5 MPa, which was 2.6 times superior to the joints without this interlayer.

Constructing heterointerfaces in heterostructures could effectively enlarge the electroactive sites and enhance the interfacial charge transfer, and thus improve the electrocatalytic performances. Herein, free-standing porous Ni2P-Ni5P4 heterostructured arrays are successfully prepared through in situ phosphating Ni(OH)2 arrays by simply tuning the reaction temperatures. Contributing from the interfacial coupling effects of two phases, large surface areas, highly conductive support of carbon cloth substrates and unique free-standing arrays, Ni2P-Ni5P4 heterostructured arrays show the enhanced kinetics and electrocatalytic performances for the hydrogen evolution reaction, oxygen evolution reaction and overall water splitting. Our research might offer insight into constructing heterophase junctions for efficient overall water splitting.

Rational design and fabrication of advanced electrodes with tailored functionality is of great significance for high-performance asymmetric supercapacitors. Herein, we report the preparation of Fe2O3 nanotube arrays and core-branch NiO nanotube arrays directly on carbon paper by using ZnO nanorods as sacrificial templates via similar synthesis process, which works anode and cathode electrodes for the asymmetric supercapacitors. Benefiting from the free-standing nanotube nanostructures, a large number of surface active sites and fast ion diffusion paths, the Fe2O3 and NiO electrodes could achieve the high capacity up to 81.9 mAh g−1 and 119.7 mAh g−1, respectively. Further, an asymmetric supercapacitor is also assembled by using Fe2O3 as anode and NiO as cathode, which shows a high energy density of 48 Wh kg−1 at the power density of 2089 W kg−1. Current research may put a general route for constructing high-performance anode and cathode materials in energy storage devices.

Herein, a general strategy is provided to construct N-doped carbon-confined MoO2 and MnO by the hydrothermal process, polymerization process and carbonation process, which serves as negative electrode and positive electrode for hybrid supercapacitors. The N-doped carbon as shell can provide fast electron pathways and short ion diffusion paths, resulting in the improved performances at the high rates. Consequently, the obtained N-doped carbon-confined MoO2 and MnO possess the good electrochemical performances, including high specific capacitance, excellent cycling stability and good rate capability. Furthermore, the as-fabricated hybrid supercapacitor using N-doped carbon-confined MoO2 and MnO shows a high energy density up to 44.82 Wh kg−1 at a power density of 900 W kg−1, as well as good cycling performance. This work may provide a general strategy for constructing high-performance energy storage devices.

Hollow nanostructures with high complexity in shell architectures have attracted tremendous interest in electrode materials for energy storage and conversion because of their unique structural features. However, the synthesis of delicate structures for hollow metal sulfides are still difficult. Herein, we demonstrate the designed synthesis of porous quadruple-shelled CoS2 hollow dodecahedrons with the concave surfaces through a template engaged formation process. Uniform yolk-shell Co3O4 dodecahedrons are first synthesized from zeolitic imidazolate framework-67 and then transformed into quadruple-shelled CoS2 hollow dodecahedrons through the reaction with sulfur powder. As the result of the assembly of the advantages from materials and structures, when evaluating as electrodes for supercapacitors, the porous quadruple-shelled CoS2 shows a high specific capacity of 375.2 C g−1 with a good rate performance and excellent stability with 92.1% retention after 10000 cycles. Moreover, the assembling quadruple-shelled CoS2//active carbon asymmetric supercapacitor achieves a high energy density of 52.1 Wh kg−1, excellent specific capacitance (146 F g−1 at 0.5 A g−1), and electrochemical cycling stability (89% retention after 5000 cycles). The improved electrochemical performance of quadruple-shelled CoS2 hollow dodecahedrons demonstrates the importance of design of hollow electrodes materials with higher complexity.

Here, by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy, we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0–4.8 V). We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases. These Li-deficient phases exhibit structure distortion with superstructure stripes, likely caused by the migration of the vanadium, which can slow down the lithium ion diffusion or even block the diffusion channels. Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss. Thus, the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling. After 500 cycles, the thickness of active LVP layer decreases to be ∼ 5–20 nm. Moreover, the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated, indicating the thick SEI film also contributes to the capacity loss. The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale, which is essential to understand the voltage fading and capacity decaying of LVP cathode.

Brazing C/SiC composites to Ti6Al4V alloy is associated with the problem of high residual stress inducing low joining strength. To overcome this problem, negative thermal expansion Zr2P2WO12 (ZWP) nanoparticles were introduced into AgCu brazing alloy to obtain robust C/SiC-Ti6Al4V joints. Microstructures and mechanical properties of the joints brazed with different ZWP contents were investigated. Results indicated that 3 wt% ZWP nanoparticles dispersed homogeneously among brazing seam and compatible with brazing alloy. The width of reaction layer at C/SiC side was reduced sharply. Meanwhile, the finite element analysis showed that residual stress was reduced by 52.9 MPa and stress concentration among reaction layer was eliminated. The average shear strength of the joints brazed with AgCu + 3 wt% ZWP increased to 146.2 MPa, which was 70.8% higher than that of joints brazed without ZWP.

Herein, we successfully design and construct core-shell nanostructured NiCo2S4@Ni3S2 directly on Ni foam by a scalable and effective one-step strategy. Further, through simply and accurately controlling the concentration of sulfur source, various nanostructures of NiCo2S4@Ni3S2 arrays in situ on Ni foam are successfully synthesized. The intriguing core-shell structures and integrated electrode configurations endow NiCo2S4@Ni3S2 electrode a large electroactive sites, fast electron transport path and sufficient contacts with electrolyte. Serving as free-standing electrode, as-fabricated NiCo2S4@Ni3S2 arrays exhibit the high specific capacity (4.55 C cm−2 at 5 mA cm−2), good rate performance and good cycling stability. Impressively, current research provides a general, scalable and effective one-step strategy for constructing core-shell nanostructures for energy storage devices.

Vacancy engineering or element doping has been extensively developed to tune the electrocatalytic activity of electrocatalysts. However, it is challenging to simultaneously generate doping and defects, and insights into the structure–property relationship in vacancy-rich and doped catalysts are lacking. Herein, a V-doped NiCoP electrocatalyst is developed through utilizing the V-doping effect enhanced by P vacancies via plasma treatment. The P vacancies can enhance the V doping effect to increase the electroactive sites and regulate the electron density of the active site center. Thus, an enlarged electrochemical active area, accelerated electron transportation and promoted electronic coupling effects can be achieved. As a result, the overpotentials at a current density of 10 mA cm−2 are 58 and 246 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, respectively. When serving as a bifunctional electrode for overall water splitting, V-doped NiCoP with P vacancies can achieve a low voltage of 1.55 V at 10 mA cm−2. This work highlights a feasible strategy to explore efficient electrocatalysts via the heterogeneous atom doping effect enhanced by vacancies.

Strong chemical bonds between transition metal oxides and carbon materials which enable fast electron transfer kinetics are highly required in supercapacitor electrodes. Meanwhile, hollow transition metal oxide nanostructures have promising potential for advanced energy storage applications. Herein, an oxygen vacancy assisted hydroxyl modification method is proposed to encapsulate Mn3O4 hollow spheres with controlled shell numbers in reduced graphene oxide (Mn3O4–rGO). The strong bonds between Mn3O4 and graphene result in fast charge transport, uniform distribution, increased active sites and enhanced structural stability. Originating from the structural features, when these materials were evaluated as electrodes for supercapacitors, Mn3O4–rGO shows a high specific capacitance of 561.5 C g−1 with good rate performance and excellent stability with 98% retention after 10 000 cycles. In order to widen the potential application of supercapacitors, asymmetric supercapacitors (ASCs) are assembled using Mn3O4–rGO as positive electrodes and active carbon as negative electrodes. The ASCs exhibit a high specific capacitance of 180.2 F g−1, delivering a high energy density of 72.3 W h kg−1 at a power density of 864 W kg−1. This surface-confined strategy may pave a way for realizing strong chemical bonds between hollow oxides and carbon-based materials for high performance supercapacitors.

The electrochemical performance of nanostructured nickel-cobalt sulfides is greatly limited by the sluggish reaction kinetics and limited electroactive sites. Herein, we design and synthesize free-standing Se doped nickel-cobalt sulfides with controllable-component directly on carbon cloth, which involves the hydrothermal process and sulfuration/selenylation reaction. Serving as free-standing electrode, as-synthesized Se doped nickel-cobalt sulfides not only favor the fast ion diffusion path and low contact resistance, but also provide rich electroactive sites with electrolyte. More importantly, proper Se doping in nickel-cobalt sulfides greatly increases the electrochemically active surface area and reduces the charge transfer resistance. Based on the X-ray photoelectron spectroscopy and transmission electron microscopy results, the reaction mechanism is convincingly revealed that Se dopants have been changed into SeOx. And electrochemical activated oxyhydroxides are mainly involved in electrochemical reactions. As a result, as-fabricated Se doped nickel-cobalt sulfides show a good electrochemical performance for supercapattery. Further, the supercapattery device is also assembled by using nickel-cobalt sulfide/selenide as positive electrode and activated carbon as negative electrode, which shows a high energy density of 39.6 Wh kg−1 at the power density of 1501 W kg−1.

High electrochemical performance of supercapacitor electrodes largely rely on the smart design of nanoarchitectures with scrupulous combination of different active materials. We present a facile method for the multicomponent design of hierarchical Co9S8 hollow nanotubes (CS NTs) wrapped with Ni-Co layered double hydroxides nanosheets (Ni-Co LDH NSs) core-shell high-performance supercapacitors. The CS NTs serve as an ideal backbone with pentagonal cross-section to enhance the conductivity for acting as a “superhighway” for electron transport, whereas the Ni-Co LDH NSs with high electrochemical activity electrodeposited on the surface of CS NTs provide the electroactive sites and enhance the structural stability for faradaic reaction. The CS NTs@Ni-Co LDH NSs hierarchical electrode presents a high specific capacitance of 1020 C g−1 and high cycling stability of 90.4% after 10,000 cycles. Moreover, an asymmetric supercapacitor (ASC) was assembled with CS NTs@Ni-Co LDH NSs as the anode and active carbon as cathode. The as-fabricated ASC shows high energy density of 50 Wh kg−1 and exhibit superior cyclic stability of 86.4% retention over 5000 cycles, suggesting this electrode is promising for efficient electrochemical capacitors.

Carbon nanomaterials have been widely used to enhance the performance of MnO2-based supercapacitors. However, it still remains a challenge to directly fabricate high combining strength, mesostructured and high-performance MnO2/carbon nanotube (CNT)-nanostructured composite electrodes with a little weight percentage of carbon materials. Here, we report a novel mesostructured composite of the CNT-on-MnO2 nanosheet with a high MnO2 percentage, which consists of vertically aligned MnO2 nanosheets with nanopores and in situ formed oriented CNTs on MnO2 nanosheets (tube-on-sheet). The optimized CNTs/MnO2 possesses favorable features, namely, vertically aligned nanosheets to shorted ion diffusion path, a hierarchical porous structure for increased specific surface areas and active sites, and in situ formed CNTs for enhanced conductivity and robust structural stability. It is found that the unique tube-on-sheet CNTs/MnO2 nanocomposites with the high MnO2 percentage (>90 wt %) exhibit a high specific capacity of 1...

Developing efficient and low-cost electrocatalysts for the oxygen evolution reaction and hydrogen evolution reaction is urgently needed for overall water splitting. Herein, three dimensional core-branch Ni3S2/Co9S8 arrays are directly grown on Ni foam by controllably sulfidizing NiCo-precursor with different concentrations of sulfur source. The unique core-branch Ni3S2/Co9S8 arrays provide large surface active areas for electrochemical reactions, open channels for effective gas release and intimate contact with Ni foam for fast electron transport. Serving as a free-standing electrocatalytic electrode, the as-synthesized Ni3S2/Co9S8 arrays show outstanding catalytic activity with an overpotential of 340 mV and 269 mV for oxygen evolution reaction and hydrogen evolution reaction at a current density of 100 mA cm−2 in 1 M KOH, respectively. Moreover, Ni3S2/Co9S8 works as a bifunctional electrocatalyst for overall water splitting, where the low cell voltage of 1.55 V at 10 mA cm−2 and good cycling performance can be successfully achieved. This work provides a facile strategy to construct core-branch nanostructures for an efficient bifunctional electrocatalyst for overall water splitting.