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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.

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.

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.

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.

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.

The brush surface structure of SiCf/SiC has been designed to obtain the robust SiCf/SiC-alloy joint by reducing the residual stress and improving interface bonding. SiC fibers are exposed through thermal corrosion at a low temperature, forming the transition layer of SiC fiber-reinforced AgCuTi. The transition layer replaces the original plate reaction layer, which increases the joining area effectively and forms the 3D network of the reaction layer. The crack propagation is hindered, and SiC fibers increase the interfacial bonding. The residual stress is reduced by decreasing the property mismatch between SiCf/SiC and alloy with this transition layer. All these improvements contribute to the high shear strength. The shear strength of joints reached 41.4 MPa with the transition layer of 67 μm, twice higher than that of original joints of 20.7 MPa.

Brazing SiO 2 -BN ceramic to Ti6Al4V is often associated with the problem of brittle continuous phases and high residual stress at the reaction layer of SiO 2 -BN, inducing low joining strength. To overcome these problems, SiO 2 -BN ceramic modified with in situ synthesized carbon nanotubes (CNTs) were joined to Ti6Al4V by TiZrNiCu alloy. Results show that CNTs can improve the wettability of TiZrNiCu on SiO 2 -BN rapidly, and break the continuous reaction layer of SiO 2 -BN into fine sizes. Residual stress can also be reduced by low CTE of CNTs and fine size phases among reaction layer. The shear strength of SiO 2 -BN/Ti6Al4V joints with CNTs modified is 35.3 MPa at 970 °C for 10 min, which is 3 times higher than that of the joints without CNTs modified.

Brazing SiO2-BN with Ti6Al4V is often associated with the problems of high residual stress and excessive Ti-based compounds formed. To overcome these problems, we report a new type interlayer of carbon nanotube (CNT) reinforced Ni foam fabricated by plasma enhanced chemical vapor deposition. The in-situ grown CNT are homogenously dispersed on 3D structure Ni foam, which could effectively avoid damage and agglomeration in the brazing seam. Result shows that Ni foam could consume excessive dissolved Ti, and CNT was beneficial for restricting the growth of phase, improving joining strength and releasing residual stress rapidly. The average shear strength of the joint brazed with CNT-Ni foam is about 50 MPa, and this value is about 5 times higher than that of joints brazed with pure TiZrNiCu. Further, a new simulated experiment was carried out innovatively to solving the difficulty of investigating interfacial behavior of CNT in brazing seam. Then the results clarify that integral structure of CNT can prevent the reaction with Ti. In situ growth of CNT on Ni foam could provide a way for introducing CNT into brazing seam without damaging structure of CNT.

Here, the core-core-shell architectural hybrid electrodes were successfully fabricated by coating of NiO nanosheets on Cu 2 O nanorod arrays with the help of carbon layers (NiO@C@Cu 2 O NAs), which was directly grown on Cu foam as battery-like electrode for supercapacitor. Starting from commercial Cu foam, the whole synthesis process mainly involved sequential solution immersion, a carbonization treatment and hydrothermal reaction, all of which were simple and potentially scalable. This core-core-shell hierarchical architecture can not only shorten ion diffusion path and optimize charge transport, but also enhance contact surface area. In addition, the carbon layer as an intermediate layer can shorten the charge transfer distance and protect the structural stability of Cu 2 O. Moreover, ultrathin nanosheet-like NiO coated on the C@Cu 2 O backbones can provide more contact area with the electrolyte, which is beneficial for the improvement of areal specific capacitance. Serving as the supercapacitor electrodes, the resulting NiO@C@Cu 2 O NAs hybrid electrodes exhibited excellent performance, e.g. high specific capacitances of 2.18 F cm −2 , and a superior long-cycle lifetime and high cycling stability (91.5% after 10,000 cycles). Such enhanced NiO@C@Cu 2 O NAs with core-core-shell hybrid structure are promising battery-like electrode for supercapacitors in future applications.

The joining of SiO 2f /SiO 2 to TC4 alloys suffers from the problems of poor wettability with AgCuTi, excessive Ti dissolving from TC4 and emergence of high residual stress among the joint. To solve these problems, an effective method by coating graphene on the SiO 2f /SiO 2 is developed. Wetting experiments confirm that contact angle notably reduces from 131° to 42.8° after coating rGO. Further, rGO react with Ti element from the brazing alloy and TC4 alloy, inhibiting the formation of excessive brittle reaction layer and in situ forming TiC reinforcement. The highest shear strength of SiO 2f /SiO 2 -TC4 brazed joints was up to 39.2 MPa.

Brazing C/C composites to TC4 is often associated with the problems of excessive Ti and high residual stress, which results in low-strength joints. To overcome these problems, AgCu brazing alloy incorporated with Si3N4 or SiO2 particles was used to join the C/C composites to TC4 alloy. The effect of Si3N4 or SiO2 particles on the microstructure and mechanical properties of brazed joints was investigated in detail. Results show that Si3N4 or SiO2 particles can react with Ti element from TC4, which is beneficial to inhibit too many brittle compounds at the C/C side. Meanwhile, it can in situ form the homogeneous distribution of fine-grained Ti based compounds during the brazing process. Due to their fine size, uniform distribution, and favorable cohesion with the matrix, the in situ Ti based compounds as reinforcements have excellent reinforcing effects in the brazing seam. Finite element analyze was adopted to investigate the residual stress state of the joins, and the result shows that the addition of silicide particles can reduce the residual stress obviously. The highest average shear strength reached about 45 MPa for Si3N4 and 41 MPa for SiO2 particles additions, which was higher than that of joints brazed using pure AgCu.

Due to the poor wettability with AgCuTi and high residual stress, it is difficult to achieve high-strength brazed joint of SiO 2f /SiO 2 (quartz fiber reinforced silica) with metals. Herein, plasma treatment as an effective approach was conducted to modify the surface state of SiO 2f /SiO 2 for better wettability and high-strength brazed joints. Based on SEM, Raman, XPS and wetting experiment analysis, the mechanism of plasma treatment on the improved wettability of SiO 2f /SiO 2 with AgCuTi is proposed. Plasma treatment can coat thin carbon film and form C-Si bonding on the surface of SiO 2f /SiO 2 , which both show good wettability with AgCuTi. Therefore, the contact angle was notably reduced from 131° to 45° with only 5min plasma treatment on the SiO 2f /SiO 2 . Afterwards, the effect of plasma treating time on the interfacial microstructure and mechanical property of SiO 2f /SiO 2 -Nb joints were investigated in detail. It was found that adjusting the plasma treating time can control the distance of brazing alloy infiltration. Further, the shear strength and the fracture morphologies were closely related with the distance of brazing alloy infiltration. The infiltration of AgCuTi at the SiO 2f /SiO 2 side can significantly increase the bonding areas and reduce residual stress, and thus enhance the mechanical properties of brazed joints.

Highlights Freestanding Mo-doped NiCoP nanosheets are designed as bifunctional electrocatalysts for overall water splitting.Remarkable electrocatalytic performances are achieved by Mo doping, where a low-water-splitting voltage of 1.61 V at 10 mA cm−2 is obtained. Electronic supplementary material The online version of this article (10.1007/s40820-019-0289-6) contains supplementary material, which is available to authorized users., Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes, serving as bifunctional electrocatalysts for overall water splitting. Notably, Mo doping could effectively modulate the electronic structure of NiCoP, leading to the increased electroactive site and improved intrinsic activity of each site. Furthermore, an electrochemical activation strategy is proposed to form Mo-doped (Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction. Benefiting from the unique freestanding structure and Mo doping, Mo-doped NiCoP and (Ni,Co)OOH show the remarkable electrochemical performances, which are competitive among current researches. In addition, an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm−2. Therefore, this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation. Electronic supplementary material The online version of this article (10.1007/s40820-019-0289-6) contains supplementary material, which is available to authorized users.

A novel type negative expansion β-LiAlSiO4 (LAS) particles reinforced Cu composites was fabricated to reduce the generation of residual stress in C/C–Nb joints brazed with AgCuTi. LAS-Cu composite layer could disperse high-content LAS particles uniformly among brazing seam. It induced the gradient change of coefficient of thermal expansion (CTE) from C/C to Nb. High stress among brazing seam was weakened and C/C interface presented low stress condition. Cu matrix also maintains the activity of brazing alloy to form reliable bonding of C/C interface. The shear strength of joints modified with 40 vol% LAS-Cu interlayer was 40.9 ± 2.8 MPa, which was 2.3 times more than that of original joints.