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The exploration towards cost-effective filler metal for ceramics joining has always been the key issues for ceramics joining. Herein, we reveal that the Al metal prefers to spread on the ZrO2 based ceramic under the air heating condition, due to the geometric limit effects by in-situ formed dense Al2O3 surface. Inspired by this, the joining of ZrO2 based ceramics was realized in air with Al metal as filler, through the diffusion of Al towards ceramic side. The Al element can induce obvious interfacial bonding effect on Al2O3 layer and ZrO2 ceramic, where the hybridization among the Al-p, Zr-d and O-p orbitals plays a key role. The in-situ formed Al2O3 layer on Al filler surface is vital for forming the fine interface (shear strength of ∼36 MPa), which results in the relief of lattice mismatch and peak stress at ceramic-filler metal transition interface.

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.

Electrocatalysis is vital towards the construction of future hydrogen economy, which exerts the critical significance on the macro preparation of nanostructured electrocatalysts. Herein, a fast micro-nano liquid layer induced construction (MLC) strategy is proposed, ensuring a tenfold increase on electrode size with almost negligible heat consumption. As a model-of-concept application, the cations coupled FeOOH nanosheets of thousands of square centimetres are synthesized within 20 minutes at room temperature for water splitting. The density functional theory (DFT) calculations further reveal that the modulation of binary cations (Ni, Zr) leads to the charge accumulation around Fe sites. This results in a more balanced proton adsorption for HER, as well as a lowered energy barrier for OER. As proposed strategy paves a technique for the scaled-up synthesis of nanostructured electrocatalysts, and also provides a platform for exploring more functional nanostructured compounds.

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.

Herein, porous Co3O4-CoO heterostructured nanosheets are constructed by plasma treatment. The density-functional theory calculations demonstrate that constructing Co3O4-CoO heterostructures modify the electronic structure to achieve enhanced electrical conductivity, but also boost the charge transfer to realize enhanced surface reactivity. Contributing to the short ion diffusion path, the rich electroactive surface sites and enhanced charge transfer capability, the resulting Co3O4-CoO nanosheet arrays possess the low overpotential of 270 mV at 10 mA cm−2 and the low Tafel slope of 49 mV dec−1. This work provides a novel strategy to construct heterostructured nanosheet arrays by surface reorganization for cost-effective OER electrocatalyst.

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.

Dual cation doping engineering can achieve high-performance electrocatalysts through the synergic effects between the two cation dopants. Here, we report a dual cation (Fe, Zn)-doped CoP core–shell nanostructure (Fe/Zn-CoP) derived from a metal–organic framework as a robust electrocatalyst. In this strategy, the introduction of Fe not only changes the morphology to provide abundant active sites, but also modifies the electronic structure of CoP to improve intrinsic activity. Furthermore, the Zn element as a sacrificial dopant can expose more active sites to boost the catalytic reaction. Consequently, the Fe/Zn-CoP core–shell arrays exhibit low overpotentials of 75 mV for the hydrogen evolution reaction (HER) and 267 mV for the oxygen evolution reaction (OER) at 10 mV cm−2 in an alkaline medium. When employed as both the anode and the cathode, Fe/Zn-CoP needs a low cell voltage of only 1.59 V to achieve 10 mV cm−2. This work highlights a feasible method for combining nanostructure design and dual cation doping to prepare highly efficient electrocatalysts.

Herein, NiS/VS heterostructures are designed as efficient electrocatalysts for overall water splitting. Vanadium modifies the electronic structure and induces a large amount of active sites. Strong interactions between the interfaces of the heterostructure lead to lower charge transfer resistance and enhance the intrinsic activity of active sites. As a result, NiS/VS only needs a potential of 158 mV for the HER and 240 mV for the OER to achieve 10 mA cm−2. When used in a two-electrode electrolyzer, NiS/VS can achieve 10 mA cm−2 at a low voltage of 1.64 V. Our research may provide a new approach for constructing bifunctional heterostructure electrocatalysts for highly efficient overall water splitting.

The interfacial behaviors of the filler metal and base material have always been the key issues for ceramics joining. Herein, we reveal that the Al metal prefers to spread on the ZrO2 based ceramic under the air heating condition, due to the geometric limit effects by in-situ formed dense Al2O3 surface. Inspired by this, the joining of ZrO2 based ceramics was realized in air with Al metal as filler, due to the diffusion of Al towards ceramic side. The Al element can induce obvious interfacial bonding effect towards Al2O3 layer and ZrO2 ceramic, where the hybridization among the Al-p, Zr-d and O-p orbitals plays a key role. The in-situ formed Al2O3 layer on Al filler surface is vital for forming the fine interface (shear strength of ~36 MPa), which results in the relief of lattice mismatch and peak stress at ceramic-filler metal transition interface.

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.

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.

Developing high-efficiency, low-cost electrocatalysts for water splitting is important but challenging. Two-dimensional nanosheet manganese dioxide (MnO2) arrays are promising candidates for the design and development of advanced catalysts because of their large surface area. Here, a feasible solution to improve the catalytic activity of MnO2 materials via decorating the active sites on the surface is proposed. With the help of plasma engineering, we successfully enabled surface activity of the MnO2 nanosheets by decorating P or Fe species together with rich vacancies on the surface. The decorated P (P-MnO2) or Fe (Fe-MnO2) species were highly beneficial for the absorption of protons and OH− respectively, and rich oxygen vacancies induced the formation of stable Mn3+, which contributed to electron and charge transfer. Thus, increased electrochemically active specific areas, accelerated charge transfer, and a proper surface electronic structure could be achieved. On the basis of this activation strategy, the fabricated P-MnO2 and Fe-MnO2 showed excellent catalytic performance for the hydrogen evolution and oxygen evolution reactions. To our knowledge, the performance of P-MnO2 and Fe-MnO2 outperformed most MnO2-based electrocatalysts in the field of electrocatalytic water splitting. Surface activation of two-dimensional MnO2 materials by decorating active species via plasma treatment can provide a feasible route for modulating the performance of earth-abundant electrocatalysts for practical applications.

Herein, porous Co

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 Ni

Arc stability and cutting quality of flux-cored arc cutting (FCAC) process were characterized using gas-forming wire and exothermic wire. The measured values of voltage and current fluctuated greatly during cutting process. Arc extinction phenomena was very common for underwater FCAC process. The variation coefficient of arc voltage and the form of arc voltage histogram were the best indicators to evaluate cutting process. Gas-forming wire and exothermic wire functioned differently in FCAC process. With increasing arc voltage, cutting process became unstable while cutting quality was improved. An increase in wire feeding speed would increase the consumption of wires, and the high proportion of arc extinction decreased the stability of the cutting process. Low cutting speed would deteriorate cutting arc stability. Successful cut could be achieved at all investigated cutting parameters. Cutting quality were evaluated using indexes include cut width, cut bevel angle, cut edges straightness, bridging degree and residual metal on the backside of the cut.

Nanotube arrays have shown great potential in a variety of important applications, such as hybrid supercapacitors. In order to endow nanotubes with multifunctionality, rationally designed and fabricated nanotube arrays with controllable structures are highly desired, but still remain a great challenge. Herein, we report a facile synthesis strategy for core-branched CoSe2/Ni0.85Se nanotube arrays directly on Ni foam by simply selenizing Co-precursor nanowires for hybrid supercapacitors. This structure design could not only ensure the intimate contact of self-branched heterostructures, but also offer sufficient active sites for electrochemical reactions. Further, we propose an electrochemical activation strategy to fully boost the electrochemical performance of CoSe2/Ni0.85Se nanotube arrays. After electrochemical activation, CoSe2/Ni0.85Se nanotube arrays have been changed into porous CoOOH/NiOOH, accounting for the remarkable performance. Contributed to by short ion diffusion paths, large electroactive sites and low contact resistance, the CoSe2/Ni0.85Se electrode after electrochemical activation shows remarkable performance for hybrid supercapacitors.

Real-time electric signal data, microstructure characteristics and mechanical properties at six different heat inputs (16 kJ/cm ∼39 kJ/cm) in underwater wet flux-cored arc welding (FCAW) of E40 steel were investigated. The electric signal results showed that the arc stability would deteriorate at high heat input because of the formation of spatters. The heat input changed the chemical composition of weld metal. With increase in the heat input, the ultimate tensile strength and impact toughness of weld metal increased due to solid solution strengthening of alloying elements. Moderate heat input (22 kJ/cm and 25 kJ/cm) was optimum, good arc stability was obtained and mechanical properties was excellent. The heat input had limited effect on the hardness of CGHAZ although the cooling rate slowed down.

Interface structures and behaviors are omnipresent in heterogeneous materials joining. Herein, we reveal that the third alloying element (typically Ti and In) would exert obvious effects not only on the interfacial structure between base material and filler, but also on the phase boundary properties of the main solid solution in the filler. The interface integration depends mainly on the bonding between Ag-based and Cu-based solid solution, which mainly originates from the hybridization among the p and d orbitals electrons. The emergence of Ti or In changes the electron orbital hybridization type between Ag-based and Cu based solid solution. Importantly, the In leads to the tightest electron cloud crossover and maximum interface separation energy, which results in the best mechanical performance (shear strength of ~300 MPa) of cemented carbide/316L stainless steel heterogeneous metal joint.

Underwater wet flux-cored arc welding of Q460 steel using specially developed Ni-based filler and commercially obtained ER308 were investigated. Wet welded joints using Ni-based filler were of high performance with high ultimate tensile strength (518 MPa) and impact toughness of the weld metal (128.9 J/cm 2 ). ER308 failed to acquire sound welded joints due to extensive slag remained in the bottom of groove. The highest microhardness (450 HV) was recorded on the coarse-grained heat-affected zone of the base metal for both joints. TypeⅡboundaries existed in the interfaces between austenitic weld metal and ferritic base metal. Compared to austenitic stainless steel weld metal, nickel-based weld metal possessed the ability to be significantly diluted by Q460 base metal.

Underwater wet welding of 316L stainless steel was performed with specially designed nickel-based tubular wire at shallow water. Microstructural observations showed that fully austenitic weld metal without cracks and pores was achieved by the nickel-base filler materials. The ultimate tensile strength of welded joints was 508 MPa and the average elongation of the joints was up to 32%. The impact test results indicated that all specimens exhibited ductile fracture and Charpy impact toughness value of weld metal at 0 °C was 159 J/cm2. The average hardness of weld metal was 156 HV. There was a sharp increase of hardness occurred in fusion zone due to more ferrite formation.

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.

Herein, in order to promote the scaled-up manufacturing of efficient nanostructured electrocatalysts, we pioneer a novel ultrafast wet chemistry engineering to turn bulk Co-Ni foam into S activated hydroxide based nanosheets (CoNi-OH|S), with short period less than six minutes. The uniform nanosheets morphology is in-situ formed through designed nitro-hydrochloric acid enhanced corrosion within 30 s, then the nanosheets are naturally oxidized to CoOOH/Ni(OH)2 (CoNi-OH) when drying in the air. To fully boost the electrochemical activities, S activation is conducted through facile chemical bath in S anion-rich aqueous solution with five minutes. The as formed surface sulfur species could optimize the protons adsorption, thus benefitting the HER electrocatalysis. Besides, the Co3+ sites with low coordination are also increased by S activation, which could facilitate the de-protonation of OOH, thus promoting the OER electrocatalysis. Finally, such ultrafast surface engineering derived CoNi-OH|S electrodes afford the relatively low overpotentials of 167 mV for HER and 270 mV for OER at 10 mA cm−2. This wet chemistry strategy further ensures that the large area self-supported electrodes can be easily prepared within several minutes, which would inspire the large-scale synthesis and practical application of similar electrocatalysts in this field.

Constructing well-defined nanointerfaces is vital to enhance the catalytic performances through electronic coupling effects from different components. However, it is still a challenge to construct metal selenides-based interfacial nanomaterials with satisfactory oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances for overall water splitting. Herein, sandwich-like structured NiSe2/Ni2P@FeP nanosheet arrays are rationally constructed, which starts from NiSe2 arrays directly on carbon cloth as backbones, followed by coating FeP nanoparticles on the backbones through the phosphorization process. Further, abundant nanointerfaces with rich defects and disordered structure are constructed during the phosphorization process, which can boost the charge transfer rate and provide rich electroactive sites. Consequently, as-synthesized NiSe2/Ni2P@FeP nanosheet arrays exhibit good HER and OER performances with small overpotentials, low Tafel slopes and good stability. Further, the overall water splitting device built by NiSe2/Ni2P@FeP exhibits a voltage of 1.554 V to attain 10 mA cm−2. Our current work may provide some new insights on rationally constructing nanointerfaces with rich defects to boost the catalytic performances for overall water splitting.

Herein, we successfully design and construct core-shell nanostructured NiCo