Search

This study explores the structural characterization of six noncovalent polyphenol-starch complexes and their prebiotic activities during in vitro digestion and fermentation. Ferulic acid, caffeic acid, gallic acid, isoquercetin, astragalin, and hyperin were complexed with sweet potato starch (SPS). The polyphenols exhibited high binding capacity (>70%) with SPS. A partial release of flavonoids from the complexes was observed via in vitro digestion, while the phenolic acids remained tightly bound. Molecular dynamics (MD) simulation revealed that polyphenols altered the spatial configuration of polysaccharides and intramolecular hydrogen bonds formed. Additionally, polyphenol-SPS complexes exerted inhibitory effects on starch digestion compared to gelatinized SPS, owing to the increase in resistant starch fraction. It revealed that the different complexes stimulated the growth of Lactobacillus rhamnosus and Bifidobacterium bifidum , while inhibiting the growth of Escherichia coli . Moreover, in vitro fermentation experiments revealed that complexes were utilized by the gut microbiota, resulting in the production of short-chain fatty acids and a decrease in pH. In addition, the polyphenol-SPS complexes altered the composition of gut microbiota by promoting the growth of beneficial bacteria and decreasing pathogenic bacteria. Polyphenol-SPS complexes exhibit great potential for use as a prebiotic and exert dual beneficial effects on gut microbiota.

Bioaccessibility and bioactivity of flavonoids in lotus leaves are related to their characteristics in gastrointestinal digestion and colonic fermentation. The aim of this study is to investigate the stability of lotus leaf flavonoids (LLF) in simulated gastrointestinal digestion, and its modulation on gut microbiota in vitro fermentation. Results showed that LLF mainly consisted of quercetin-3-O-galactoside, quercetin-3-O-glucuronide, quercetin-3-O-glucoside, and kaempferol-3-O-glucoside. These flavonoids kept stability with only a small fraction degraded in simulated gastric and intestinal fluids. In vitro fermentation, LLF stimulated the growth of Actinobacteria and Firmicutes, inhibited the growth of Proteobacteria, and induced the production of fermentation gases and short-chain fatty acids. Interestingly, supplementation of soluble starch significantly improved the utilization of LLF by the intestinal flora. These results revealed that LLF shaped a unique biological web with Lactobacillus and Bifidobacterium spp. as the core of the biological network, which would be more beneficial to gut health., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The sonoprocessing of droplet spreading during the wetting process of molten aluminum droplets on SiC ceramic substrates at 700 °C is investigated in this paper. When wetting is assisted by a 20 kHz frequency ultrasonic field, the wettability of liquid metal gets enhanced, which has been determined by the variations in thermodynamic energy and wetting kinetics. Wetting kinetic characteristics are divided into two stages according to pinning and depinning states of substrate/droplet contact lines. The droplet is static when the contact line is pinning, while it is forced to move when the contact line is depinning. When analyzing the pinning stage, high-speed photography reveals the evidence of oxide films being rapidly crushed outside the aluminum droplet. In this work, atomic models of spherical Al core being wrapped by alumina shell are tentatively built, whose dioxide microstructures are being transformed from face-centered cubic into liquid at the atomic scale. At the same time, the wetting experiment reveals that the oxide films show changes in the period of sonoprocessing from 3rd to 5th second. During the ultrasonic spreading behavior in the late stage, there is a trend of evident expansion of the base contact area. The entire ultrasonic process lasts for no longer than 10 s. With the aid of ultrasonic sinusoidal waves, the wettability of metal Al gets a rapid improvement. Both molecular dynamic (MD) investigations and the experiments results reveal that the precursor film phenomenon is never found unless wetting is assisted by ultrasonic treatments. However, the precursor film appears near the triple line after using ultrasonics in the droplet wetting process, whose formation is driven by ultrasonic oscillations. Due to the precursor film, the ultrasonic wetting contact angle is lower than the non-ultrasonic contact angle. In addition, the time-variant effective ultrasonic energy has been quantitatively evaluated. The numerical expressions of thermodynamic variables are well verified by former ultrasonic spreading test results, which altogether provide an intrinsic explanation of the fast-decreasing contact angle of Al/SiC., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH 3 NH 3 PbI 3 (MAPbI 3 ) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA + followed by the collapse of perovskite structure into 6H-PbI 2 with their critical threshold doses also determined. Interestingly, an intermediate phase (MA 0.5 PbI 3 ) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH 3 and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI 3 , providing potential strategies into material optimization., (© 2021. The Author(s).)

Harvesting energy from ambient moisture and natural water sources is currently of great interest due to the need for standalone self-powered nano/micro-systems. In this work, we report on the development of a cost-effective nanogenerator based on a carbon paper-Al 2 O 3 nanoparticle layer-carbon paper (CAC) sandwich structure, where the 3D Al 2 O 3 layer is deposited via vacuum filtration. This type of device can produce an open-circuit voltage ( U OC ) of up to 4 V and a short-circuit current ( I SC ) of ∼18 μA with only an 8 μL water droplet applied. To our knowledge, this is the highest voltage yet reported from a single moisture/water-induced electricity nanogenerator using solid oxides and carbon-based materials. A remarkable output power of 14.8 μW can be reached with an optimized resistive load. An LED with a working voltage of 3-3.2 V can operate for a short time with the power from a single CAC device exposed to one 8 μL water droplet. Furthermore, a CAC generator adsorbing as little as 2 μL water droplets every 3 min can also give a U OC of 3.63 V. We show that CAC devices provide a robust electrical output over more than 200 wet-dry cycles without any deterioration in performance. These units demonstrate much promise as cost-effective electricity generators for harvesting energy from natural sources like rainwater, tap water, snow runoff, and dew. The response time of CAC devices can be as fast as 10-100 ms, making them ideal for applications as self-powered water detectors. The generation of power in this device arises from the streaming current. To assist in the optimization of these devices, we have analyzed how their response is related to such factors as layer thickness, time interval between application of water droplets, and the volume of each water droplet.

Developing high-efficiency, low-cost electrocatalysts for water splitting is important but challenging. Two-dimensional nanosheet manganese dioxide (MnO 2 ) 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 MnO 2 materials via decorating the active sites on the surface is proposed. With the help of plasma engineering, we successfully enabled surface activity of the MnO 2 nanosheets by decorating P or Fe species together with rich vacancies on the surface. The decorated P (P-MnO 2 ) or Fe (Fe-MnO 2 ) species were highly beneficial for the absorption of protons and OH - respectively, and rich oxygen vacancies induced the formation of stable Mn 3+ , 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-MnO 2 and Fe-MnO 2 showed excellent catalytic performance for the hydrogen evolution and oxygen evolution reactions. To our knowledge, the performance of P-MnO 2 and Fe-MnO 2 outperformed most MnO 2 -based electrocatalysts in the field of electrocatalytic water splitting. Surface activation of two-dimensional MnO 2 materials by decorating active species via plasma treatment can provide a feasible route for modulating the performance of earth-abundant electrocatalysts for practical applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Integrating carbon-coating and nanostructuring has been considered as the most promising strategy to accommodate the dramatic volume expansion represented by high-capacity antimony (Sb) upon sodiation. Suitable coating source and synthetic strategy that are both economical and strong are yet to be explored. In this regard, by using renewable bio-oil as carbon source and self-wrapping precursor, robust Sb@C composite anode with Sb nanoparticles homogeneously impregnated into the cross-linked 2D ultrathin carbon nanosheets is developed via a facile NaCl template-assisted self-assembly and followed carbothermal reduction method. Such judiciously crafted interconnected macroporous framework can mitigate of mechanical stress and alleviate the volume change of inner Sb, guaranteeing high-performance sodium-ion battery anode. At a current density of 0.1 A g -1 , ultrahigh reversible capacity of 520 mAh g -1 can be achieved. Notably, a stable capacity of 391 mAh g -1 is even retained after 500 cycles at 1 A g -1 . Such a facile and cost-effective synthetic method is promising for high-performance sodium-ion batteries., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Organic-inorganic hybrid perovskites (OIHPs) have attracted extensive research interest as a promising candidate for efficient and inexpensive solar cells. Transmission electron microscopy (TEM) characterizations that can benefit the fundamental understanding and the degradation mechanism are widely used for these materials. However, their sensitivity to the electron beam illumination and hence structural instabilities usually prevent us from obtaining the intrinsic information or even lead to significant artifacts. Here, we systematically investigate the structural degradation behaviors under different experimental factors to reveal the optimized conditions for TEM characterizations of OIHPs by using low-dose electron diffraction and imaging techniques. We find that a low temperature (-180 °C) does not slow down the beam damage but instead induces a rapid amorphization for OIHPs. Moreover, a less severe damage is observed at a higher accelerating voltage. The beam-sensitivity is found to be facet-dependent that a (1 0 0) exposed CH 3 NH 3 PbI 3 (MAPbI 3 ) surface is more stable than a (0 0 1) surface. With these guidance, we successfully acquire the atomic structure of pristine MAPbI 3 and identify the characterization window that is very narrow. These findings are helpful to guide future electron microscopy characterizations of these beam-sensitive materials, which are also useful for finding strategies to improve the stability and performance of the perovskite solar cells., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2020 Science China Press. Published by Elsevier B.V. All rights reserved.)

Two-dimensional transition-metal dichalcogenides hold great potential in rechargeable lithium-ion batteries. Their electrochemical properties are closely related to the structural evolutions during lithium-ion migration. Understanding these migration/reaction mechanisms is important to help improve battery performance. Herein, we report the real-time and atomic-scale observation of phase transitions during the lithiation and delithiation for V 5 S 8 via in situ electron diffraction and high-resolution transmission electron microscopy techniques. We find that the phase transformation proceeds via a sequence of order to antisite disorder intercalation and topotactic-based conversion reaction. During the intercalation reaction, the lithium ion destroys the orderings of the interstitial V with the formation of Li/V antisite. Such a reaction is found to be reversible, i.e., the extraction of lithium from Li x V 5 S 8 leads to the recovery of V orderings. The conversion reaction involves heterogeneous nucleation of Li 2 S with 3-20 nm nanodomains, which maintain the crystallographic integrity with Li x V 5 S 8 . These findings elucidate the complex interactions between the lithium ion and host V 5 S 8 during ionic migration in solids, which should be helpful in understanding the relationship between phase transformation kinetics and battery performance.

Organic-inorganic hybrid perovskites (OIHPs) have generated considerable excitement due to their promising photovoltaic performance. However, the commercialization of perovskite solar cells (PSCs) is still plagued by the structural degradation of the OIHPs. Here, the decomposition mechanism of OIHPs under electron beam irradiation is investigated via transmission electron microscopy, and a general decomposition pathway for both tetragonal CH 3 NH 3 PbI 3 and cubic CH 3 NH 3 PbBr 3 is uncovered through an intermediate superstructure state of CH 3 NH 3 PbX 2.5 , X = I, Br, with ordered vacancies into final lead halides. Such decomposition can be suppressed via carbon coating by stabilization of the perovskite structure framework. These findings reveal the general degradation pathway of OIHPs and suggest an effective strategy to suppress it, and the atomistic insight learnt may be useful for improving the stability of PSCs., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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 NiSe 2 nanosheet arrays (A-NiSe 2 |P) through Ar plasma treatment. Owing to the increased active sites and enhanced electrical conductivity, the resulted A-NiSe 2 |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-NiSe 2 |P. Further, A-NiSe 2 |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-NiSe 2 |P may highlight the importance of element doping and vacancies in enhancing the catalytic activities in overall water splitting., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Herein, porous Co 3 O 4 -CoO heterostructured nanosheets are constructed by plasma treatment. The density-functional theory calculations demonstrate that constructing Co 3 O 4 -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 Co 3 O 4 -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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

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 2 P/Cu 3 P interfaced nanosheets for overall water splitting is demonstrated. We conduct a series of experimental parameters to adjust the nanostructures of Ni 2 P/Cu 3 P, and to get insight into the synergistic effects of interfaces and P vacancies on the catalytic activities. Notably, Ni 2 P/Cu 3 P 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, Ni 2 P/Cu 3 P 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., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Proper vacancy engineering is considered as a promising strategy to improve intrinsic activity, but it is challenging to construct rich vacancies by a simple strategy. Herein, Fe doped Ni 5 P 4 nanosheet arrays with rich P vacancies are developed via a facile phase transformation strategy. Based on systematic investigations, we have demonstrated that an optimized surface electronic structure, abundant active sites and improved charge transport capability can be effectively achieved by vacancy engineering. Consequently, Fe doped Ni 5 P 4 with rich vacancies show remarkable catalytic performances with 94.5 mV for the hydrogen evolution reaction (HER) and 217.3 mV for the oxygen evolution reaction (OER) at 10 mA cm -2 , respectively, as well as good durability. When directly employed as working electrodes, the as-obtained Fe doped Ni 5 P 4 with rich vacancies can attain 10 mA cm -2 at a low voltage of 1.59 V. This work demonstrates a feasible strategy for rationally fabricating electrocatalysts with rich vacancies via a simple phase transformation.

Constructing high-efficiency electrocatalysts is vital towards electrocatalytic water splitting, but it remains a challenge. Although Ni-based materials have drawn extensive attention as highly active catalysts, the relatively limited electroactive sites in Ni-based catalysts still remains a great issue. In order to further boost the electrocatalytic performances, heteroatom doping and interface engineering are usually adopted for modification. Here, a new strategy is developed to construct W doped NiO/NiS 2 interfaced nanosheets directly on carbon sheet, which is working as efficient and bifunctional electrocatalysts for overall water splitting. W doped NiO nanosheets are directly constructed on the carbon sheet by the hydrothermal and annealing processes. After that, W-NiO was subjected to Ar plasma assisted sulfuration treatment for forming W doped NiO/NiS 2 interfaced nanosheets. Based on systematic investigations, we find that W doping can effectively induce the modified electronic structure of Ni to boost the intrinsic activities in NiO/NiS 2 . Further, forming NiO/NiS 2 nanointerfaces can also provide rich electroactive sites and boost the charge transfer rate. Consequently, W doped NiO/NiS 2 exhibits the much enhanced performances for overall water splitting. As a bifunctional electrode, W-NiO/NiS 2 demonstrates a remarkable activity with a 1.614 V cell voltage at 10 mA cm -2 for overall water splitting., (Copyright © 2019 Elsevier Inc. All rights reserved.)

CoSb 3 -based skutterudite alloy is one of the most promising thermoelectric materials in the middle temperature range (room temperature-550 °C). However, the realization of an appropriate metallization layer directly on the sintered skutterudite pellet is indispensable for the real thermoelectric generation application. Here, we report an approach to prepare the metallization layer and the subsequent diffusion bonding method for the high-performance multi-filled n -type skutterudite alloys. Using the electroplating followed by low-temperature annealing approaches, we successfully fabricated a Co-Mo metallization layer on the surface of the skutterudite alloy. The coefficient of thermal expansion of the electroplated layer was optimized by changing its chemical composition, which can be controlled by the electroplating temperature, current and the concentration of the Mo ions in the solution. We then joined the metallized skutterudite leg to the Cu-Mo electrode using a diffusion bonding method performed at 600 °C and 1 MPa for 10 min. The Co-Mo/skutterudite interfaces exhibit extremely low specific contact resistivity of 1.41 μΩ cm 2 . The metallization layer inhibited the elemental inter-diffusion to less than 11 µm after annealing at 550 °C for 60 h, indicating a good thermal stability. The current results pave the way for the large-scale fabrication of CoSb 3 -based thermoelectric modules.

The rapid solidification of melt spinning has been widely used in the fabrication of high-performance skutterudite thermoelectric materials. However, the microstructure formation mechanism of the spun ribbon and its effects on the mechanical properties are still unclear. Here, we report the microstructure evolution and mechanical properties of La-Fe-Co-Sb skutterudite alloys fabricated by both long-term annealing and melt-spinning, followed by sintering approaches. It was found that the skutterudite phase nucleated directly from the under-cooled melt and grew into submicron dendrites during the melt-spinning process. Upon heating, the spun ribbons started to form nanoscale La-rich and La-poor skutterudite phases through spinodal decomposition at temperatures as low as 473 K. The coexistence of the micron-scale grain size, the submicron-scale dendrite segregation and the nanoscale spinodal decomposition leads to high thermoelectric performance and mechanical strength. The maximum three-point bending strength of the melt spinning sample was about 195 MPa, which was 70% higher than that of the annealed sample.

Vanadium nitride (VN) with high conductivity exhibits the potential promising as anode materials for supercapacitors, but VN suffered the obvious performance fading due to the dissolution of VN in aqueous electrolyte. In this work, we solve these problems through realizing 3D structural VN microsheets shelled with N-doped carbon layer (VN@NC) by introducing melamine as nitrogen source and PVP as carbon source. The as-prepared VN@NC electrode display high capacitance of 368 F g -1 and good rate property. A solid-state asymmetric supercapacitor (ASC) with NiCo 2 O 4 nanowires as cathode materials and VN@NC as anode materials was fabricated. The ASC device exhibits the high energy density of 65.3 W h kg -1 , and good cycling stability (92% capacitance retention) after 4000 cycles. Moreover, the ASC device shows good mechanical flexibility with negligible capacitance loss after 1000 bending cycles., (Copyright © 2019 Elsevier Inc. All rights reserved.)

With the increasing energy demand, it is very urgent to develop new anode materials for lithium ion batteries (LIBs). Designing nanostructures and constructing multicomponent metal sulfides are vital for enhancing the electrochemical performance. This study reports a new synthetic method to construct MoS2/CoMo2S4/Co3S4 nanostructures supported by graphene. A key step in the process, high temperature annealing, promotes the interdiffusion of metal sulfides to form multicomponent metal sulfides and establishes a strong C-S bond between the MoS2/CoMo2S4/Co3S4 nanostructure and graphene. The unique nanostructure and synergistic effects between the conductive graphene and the MoS2/CoMo2S4/Co3S4 nanostructure endows the material with good lithium storage. As a result, it exhibits a good rate performance (360 mA h g-1 at 10 A g-1) and a high specific capacity (770 mA h g-1 at 0.2 A g-1). This study provides a unique method to construct promising anode materials for the application of LIBs.

Rational design of self-supported electrode materials is important to develop high-performance supercapacitors. Herein, a free-standing MnCo 2 S 4 @CoNi LDH (MCS@CN LDH) core-shell heterostructure is successfully prepared on Ni foam using the hydrothermal reaction and electrodeposition. In this architecture, the inner MnCo 2 S 4 nanotube provides an ultra-high electrical conductivity and the CoNi LDH nanosheets can offer more electrochemical active sites for better faradaic reactions. Moreover, the core-shell heterostructure can also maintain the structural integrity during the processes of continuous charge/discharge. The MCS@CN LDH electrode displays a satisfactory specific capacitance of 1206 C g -1 and excellent cycling performance with ∼92% retention after 10 000 cycles. In addition, an asymmetric supercapacitor (ASC), in which MCS@CN LDH and N-doped rGO are used as the positive electrode and the negative electrode, was assembled which exhibits an energy density of 48.8 W h kg -1 with superior cycling stability, indicating the potential of this electrode in practical energy storage.

Bonding between polycrystal alumina and sapphire with (0001), (10 1 ¯ 0), (11 2 ¯ 0), (1 1 ¯ 02) orientations is successfully achieved by growing aluminium borate whiskers in the joint. The morphology of the whiskers in the joint is characterised by (Scanning Electron Microscopy) SEM. The relationship between the growing direction of the aluminium borate whiskers and the orientation of the sapphire substrate is investigated. The effect of the growing direction of the aluminium borate whiskers on the mechanical properties of the joint is discussed. The results show that the whiskers on the sapphire with (10 1 ¯ 0) orientation grow perpendicular to the surface of the substrate while the whiskers show a random growth on the other substrates. It is found that there is an orientation relationship between the whiskers (220) and sapphire (10 1 ¯ 0) and the morphology of the whiskers has great influence on the mechanical properties of the joint. The joint between polycrystal alumina and sapphire with (10 1 ¯ 0) orientation exhibits the highest strength, which reaches 26 MPa.

Owing to low-cost and 3d electronic configurations, Co 3 O 4 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 Co 3 O 4 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 Co 3 O 4 , while inducing S in Co 3 O 4 increases the electrical conductivity and provides ample S sites for proton adsorption. In addition, Mn and S dual-doping effectively increase the proportion of Co 3+ , resulting in facilitating the four-electron transfer and thus higher electrochemical activities. Consequently, the optimal Mn and S dual-doping Co 3 O 4 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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The introduction of oxygen vacancies into electrode materials has been proven to be a valid way to enhance the electrochemical performance. However, the traditional methods to introduce oxygen vacancies require severe conditions that may be harmful to hydroxides. Herein, the oxygen vacancy-rich nickel-cobalt (NiCo) layered double hydroxide (denoted as V o -NiCo LDH) nanowire array electrode is synthesized using the chemical reduction method. Owing to the reduction of NaBH 4 solution, we can create oxygen vacancies under milder conditions, thus avoiding any damage to the hydroxide. The as-synthesized electrode shows a specific capacitance of 1563.1 F g -1 at 1 A g -1 , which is much higher than that of the pristine electrode (995.4 F g -1 at 1 A g -1 ). Moreover, the cycling performance and rate performance are also enhanced. The as-fabricated asymmetric supercapacitor (V o -NiCo LDH//Fe 2 O 3 ) is able to deliver a maximum energy density of 56.2 W h kg -1 at a power density of 800 W kg -1 with a voltage window of 1.6 V., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Ti-Fe intermetallic compounds were effectively suppressed with Cu-based filler wire and weld formation was greatly improved with the preheating of substrates when joining TC4 titanium alloy and 304 stainless steel. A Ti/Cu transition zone consisting of complex TiCu, Ti 2 Cu 3 , TiFe, and TiFe 2 phases was formed between Cu-weld/TC4 interface, while Cu-weld/304ss interface was mainly composed of α-Fe and ε-Cu solid solution. At lower heat input, the undercut defect in back surface had potential to cause crack initiation and joint fracture. Though increasing heat input would improve weld morphology, the formation of thick interfacial reaction layer and weld cracking led to low weld quality and joint strength. The preheating of substrates had an obvious effect on wetting ability of liquid filler metal and could achieve a better weld quality at lower heat input. The back formation of weld was improved to decrease the occurrence of weld defects. The highest tensile strength of 365 MPa occurred at welding heat input of 0.483 kJ/cm, increasing by 47% compared to the joint without preheating. The interfacial reaction mechanism was discussed to reveal the relationship between microstructural characteristics and fracture behavior of Ti/steel welded joints with Cu-based filler wire.

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 Ni 2 P-Ni 5 P 4 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, Ni 2 P-Ni 5 P 4 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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

A method to improve the brazing between YSZ and Ti6Al4V by femtosecond laser surface machining is introduced. The highest strength of ~150 MPa (which is 95.2% higher than that of the flat YSZ/Ti6Al4V joint) is achieved when the processing speed is 200 μm/s. To understand the strengthen mechanism of the surface machining on the joint strength, image based models, based on the observed microstructure, have been used to probe the stress distribution in the joint. It is found that through surface machining on the ceramic, the residual stress distribution in ceramic becomes nonlinear. Upon shear testing, for the joint with a flat interface, the failure happens in the reaction layer and the out of plane stress in this layer is found to be tensile, which acts as the driving force for the crack generation and propagation. But for the joint with a rumpled interface, the compressive out of plane stress at the boundary of the grooves in the reaction layer could inhibit the propagation of the cracks. Finally, by surface machining on the ceramic, the maximum shear stress in the reaction layer is decreased, which could also help to improve the reliability of the joint.

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.

Intrinsically poor conductivity, sluggish ion transfer kinetics, and limited specific area are the three main obstacles that confine the electrochemical performance of metal oxides in supercapacitors. Engineered hollow metal oxide nanostructures can effectively satisfy the increasing power demand of modern electronics. In this work, both triple-shelled MnO 2 and hollow Fe 2 O 3 microcubes have been synthesized from a single MnCO 3 template. The oxygen vacancies are introduced in both the positive and negative electrodes through a facile method. The oxygen vacancies can not only improve the conductivity and facilitate ion diffusion but also increase the electrode/electrolyte interfaces and electrochemically active sites. Consequently, both the oxygen-deficient triple-shelled MnO 2 and hollow Fe 2 O 3 exhibit larger capacitance and rate capability than the samples without oxygen vacancies. Moreover, due to the matchable specific capacitance and potential window between the positive and negative electrodes, the asymmetric supercapacitor exhibits high specific capacitance (240 F g -1 ), excellent energy density of 133 W h kg -1 at 1176 W kg -1 , excellent power density (23 529 W kg -1 at 73 W h kg -1 ), and high cycling stability (90.9% after 5000 cycles). This strategy is highly reproducible in oxide-based electrodes, which have the potential to meet the requirements of practical application.

Underwater wet welding technology is widely used. Because the stability of droplet transfer in underwater wet welding is poor, the feasibility of improving the droplet transfer mode has been discussed from various technical directions. In this work, the characteristics of pulsating wire feeding were studied in the pulsating wire feeding mode by investigating the effects of changing the pulsating frequency, the wire withdrawal speed, and the wire withdrawal quantity on the droplet transfer process and the welding quality. With the aim of improving weld forming and welding stability, the authors selected the coefficient of variation and the ratio of unstable droplet transfer as the indexes to evaluate the effect of droplet transfer control. The pulsating wire feeding process of underwater wet flux-cored wire was analyzed in depth, and the following conclusions were drawn: using the pulsating wire feeding mode and after comparing and analyzing the pulsed wire feeding process under the same frequency condition, the authors found that the forming and stability were better under the conditions of slower withdrawal speed and smaller withdrawal quantity. The short-circuit transition ratio decreased steadily with the increase of pulsating wire feeding frequency, the rejection transition ratio first rose and then decreased, and the splash ratio first decreased and then rose.

Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free-standing and defect-rich heterogeneous MoS 2 /NiS 2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS 2 /NiS 2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS 2 /NiS 2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting., Competing Interests: The authors declare no conflict of interest.

Herein, we successfully design and construct core-shell nanostructured NiCo 2 S 4 @Ni 3 S 2 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 NiCo 2 S 4 @Ni 3 S 2 arrays in situ on Ni foam are successfully synthesized. The intriguing core-shell structures and integrated electrode configurations endow NiCo 2 S 4 @Ni 3 S 2 electrode a large electroactive sites, fast electron transport path and sufficient contacts with electrolyte. Serving as free-standing electrode, as-fabricated NiCo 2 S 4 @Ni 3 S 2 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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Organic-inorganic hybrid perovskites are promising candidates for the next-generation solar cells. Many efforts have been made to study their structures in the search for a better mechanistic understanding to guide the materials optimization. Here, we investigate the structure instability of the single-crystalline CH 3 NH 3 PbI 3 (MAPbI 3 ) film by using transmission electron microscopy. We find that MAPbI 3 is very sensitive to the electron beam illumination and rapidly decomposes into the hexagonal PbI 2 . We propose a decomposition pathway, initiated with the loss of iodine ions, resulting in eventual collapse of perovskite structure and its decomposition into PbI 2 . These findings impose important question on the interpretation of experimental data based on electron diffraction and highlight the need to circumvent material decomposition in future electron microscopy studies. The structural evolution during decomposition process also sheds light on the structure instability of organic-inorganic hybrid perovskites in solar cell applications.

Carbon nanomaterials have been widely used to enhance the performance of MnO 2 -based supercapacitors. However, it still remains a challenge to directly fabricate high combining strength, mesostructured and high-performance MnO 2 /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-MnO 2 nanosheet with a high MnO 2 percentage, which consists of vertically aligned MnO 2 nanosheets with nanopores and in situ formed oriented CNTs on MnO 2 nanosheets (tube-on-sheet). The optimized CNTs/MnO 2 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/MnO 2 nanocomposites with the high MnO 2 percentage (>90 wt %) exhibit a high specific capacity of 1131 F g -1 based on total electrodes and 1229 F g -1 based on MnO 2 at a current density of 1 A g -1 , high rate capability, and ultrastable cycling life (94.4%@10 000 cycles). This electrode design strategy in this paper demonstrates a new way for high-performance electrodes for supercapacitors with high active material percentage.

NiCo2S4 is a promising electrode material for supercapacitors, due to its rich redox reactions and intrinsically high conductivity. Unfortunately, in most cases, NiCo2S4-based electrodes often suffer from low specific capacitance, low rate capability and fast capacitance fading. Herein, we have rationally designed P-doped NiCo2S4 nanotube arrays to improve the electrochemical performance through a phosphidation reaction. Characterization results demonstrate that the P element is successfully doped into NiCo2S4 nanotube arrays. Electrochemical results demonstrate that P-doped NiCo2S4 nanotube arrays exhibit better electrochemical performance than pristine NiCo2S4, e.g. higher specific capacitance (8.03 F cm-2 at 2 mA cm-2), good cycling stability (87.5% capacitance retention after 5000 cycles), and lower charge transfer resistance. More importantly, we also assemble an asymmetric supercapacitor using P-doped NiCo2S4 nanotube arrays and activated carbon on carbon cloth, which delivers a maximum energy density of 42.1 W h kg-1 at a power density of 750 W kg-1. These results demonstrate that the as-fabricated P-doped NiCo2S4 nanotube arrays on carbon cloth show great potential as a battery-type electrode for high-performance supercapacitors.

The potential window of aqueous supercapacitors is limited by the theoretical value (≈1.23 V) and is usually lower than ≈1 V, which hinders further improvements for energy density. Here, a simple and scalable method is developed to fabricate unique graphene quantum dot (GQD)/MnO 2 heterostructural electrodes to extend the potential window to 0-1.3 V for high-performance aqueous supercapacitor. The GQD/MnO 2 heterostructural electrode is fabricated by GQDs in situ formed on the surface of MnO 2 nanosheet arrays with good interface bonding by the formation of Mn-O-C bonds. Further, it is interesting to find that the potential window can be extended to 1.3 V by a potential drop in the built-in electric field of the GQD/MnO 2 heterostructural region. Additionally, the specific capacitance up to 1170 F g -1 at a scan rate of 5 mV s -1 (1094 F g -1 at 0-1 V) and cycle performance (92.7%@10 000 cycles) between 0 and 1.3 V are observed. A 2.3 V aqueous GQD/MnO 2 -3//nitrogen-doped graphene ASC is assembled, which exhibits the high energy density of 118 Wh kg -1 at the power density of 923 W kg -1 . This work opens new opportunities for developing high-voltage aqueous supercapacitors using in situ formed heterostructures to further increase energy density.

NiO is a promising electrode material for supercapacitors. Herein, the novel vertically standing nanosized NiO encapsulated in graphene layers (G@NiO) are rationally designed and synthesized as nanosheet arrays. This unique vertical standing structure of G@NiO nanosheet arrays can enlarge the accessible surface area with electrolytes, and has the benefits of short ion diffusion path and good charge transport. Further, an interconnected graphene conductive network acts as binder to encapsulate the nanosized NiO particles as core-shell structure, which can promote the charge transport and maintain the structural stability. Consequently, the optimized G@NiO hybrid electrodes exhibit a remarkably enhanced specific capacity up to 1073 C g -1 and excellent cycling stability. This study provides a facial strategy to design and construct high-performance metal oxides for energy storage.

In order to confirm the key role of Ar + ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar + ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar + ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar + ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar + ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar + ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar + ion state. As for vertically oriented few-layer graphene (VFG), Ar + ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar + ion bombardment, and these special NCMs are promising in many fields.

Welding and joining of titanium aluminides is the key to making them more attractive in industrial fields. The purpose of this review is to provide a comprehensive overview of recent progress in welding and joining of titanium aluminides, as well as to introduce current research and application. The possible methods available for titanium aluminides involve brazing, diffusion bonding, fusion welding, friction welding and reactive joining. Of the numerous methods, solid-state diffusion bonding and vacuum brazing have been most heavily investigated for producing reliable joints. The current state of understanding and development of every welding and joining method for titanium aluminides is addressed respectively. The focus is on the fundamental understanding of microstructure characteristics and processing-microstructure-property relationships in the welding and joining of titanium aluminides to themselves and to other materials.