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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.

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.

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.

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.

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 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.

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.

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.

Elaborate design and synthesis of core-shell hybrid structures consisting of multiple components have been considered as the effective approach to developing electrode materials for high-performance supercapacitors. Herein, the hybrid structure consisting of CuCo2S4 core and NiMn-layered double hydroxide (NiMn-LDH) shell is hydrothermally in situ synthesized on nickel foam without organic binders as electrode materials. The resultant CuCo2S4@NiMn-LDH core-shell hybrid arrays exhibits a high specific capacitance of 2520 F g−1 at 2 A g−1, good rate capability with a long cycle lifetime. Additionally, the obtained CuCo2S4@NiMn-LDH serves as the positive electrode while the activated carbon (AC) acts as the negative electrode, which is assembled into an asymmetric supercapacitor. Impressively, the obtained asymmetric supercapacitor (CuCo2S4@NiMn-LDH//AC) delivers a high energy density of 45.8 Wh kg−1 at the power density of 1499 W kg−1. Thereby, these electrochemical performances demonstrate that as-fabricated CuCo2S4@NiMn-LDH core-shell arrays are the promising candidates as electrodes for high-performance supercapacitors.

Constructing rational structure and utilizing distinctive components are two important keys to promote the development of high performance supercapacitor. Herein, we adopt a facile two-step method to develop an in-situ heterostructure with NiCo-LDH nanowire as core and NiOOH nanosheets as shell on carbon fiber cloth. The resultant NiCo-LDH@NiOOH electrode exhibites a high specific capacitance of about 2622 F g−1 at 1 A g−1 and good cycling stability (88.5% remain after 10000 cycles). This reinforced electrochemical performance is benefit from the distinct core-shell structure, and takes advantage of the synergetic effect to supply more electrochemical active spots and pathways to accelerate electron and ion transport. Furthermore, the fabricated asymmetric supercapacitor of optimized NiCo-LDH@NiOOH//AC device displays a high energy density of 51.7 Wh kg−1 while the power density is 599 W kg−1 and presents a satisfying cycling performance.

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.

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.

Rationally constructing hybrid nanostructure electrodes is a promising approach for the development of high-performance supercapacitors. Here, we propose the fabrication of Ni3S2@Ni(OH)2 nanostructures directly on Ni foam by employing hydrothermal and chemical bath processes. In this core–shell nanostructure, the design of conductive Ni3S2 nanorods directly on Ni foam without organic binders could ensure intimate contact and fast electron transport. Meanwhile, porous Ni(OH)2 nanosheets coated on conductive Ni3S2 nanorods can effectively supply large surface areas with electrolyte and provide fast ion diffusion. Consequently, the as-fabricated Ni3S2@Ni(OH)2 nanostructures showed good electrochemical performance, such as high capacitance up to 3.55 F cm−2 and a good capacity retained after 10 000 cycles of about 85%. Furthermore, an asymmetric device, based on Ni3S2@Ni(OH)2 and activated carbon, was also fabricated and achieved a maximum energy density of 60.5 W h kg−1 at 1159 W kg−1. These results suggest that the as-designed core–shell Ni3S2@Ni(OH)2 nanostructures demonstrated in this research are promising electrode materials for energy storage.

To realize high-performance and long life span supercapacitors, highly electrochemically active materials and rational design of structure are highly desirable. Herein, a hierarchical NiCo-LDH/NiCoP@NiMn-LDH hybrid electrode (NCLP@NiMn-LDH) was synthesized on carbon cloth via a hydrothermal reaction and phosphorization treatment. Owing to the introduction of NiCoP and design of the core–shell structure, the hybrid electrode showed significantly improved electrochemical performance. The as-fabricated hybrid electrode exhibited a high specific capacitance of 2318 F g−1 at 1 A g−1, with a superior cyclic stability. Additionally, an asymmetric supercapacitor (NCLP@NiMn-LDH//AC) was assembled with a voltage window of 1.5 V. The ASC device delivered a maximum energy density of 42.2 W h kg−1 at a power density of 750 W kg−1.

Vertically-oriented few-layered graphene (VFG) has a unique three-dimensional morphology and exposed ultrathin edges, and shows great promise for high-performance supercapacitor applications. However, VFG shows limited capacitance owing to poor wettability with electrolytes, which has been a bottleneck for further applications. Herein, we designed and developed an effective strategy, based on rotary plasma etching, to create defects on the side surfaces while simultaneously maintaining the structural integrity of VFG. Rotary plasma etching decreased the contact angle (CA) of VFG from 123° to 34°, compared with conventional vertical etching, which only reduced the CA to 71°. Electrochemical studies demonstrated that VFG samples with a high density of surface defects, introduced by rotary plasma etching, exhibited a high areal capacitance of 1367 μF cm−2 (a volumetric specific capacitance of 137 F cm−3), which was approximately 4 times as large as for pristine VFG-based materials. Our study offers feasible insight into the use of an industrially viable method, rotary plasma processing, for modifying and enhancing the properties of VFG. Our findings may help to accelerate the development of more effective energy storage devices.

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.

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.

Root-like structure on C/SiC surface has been designed through selective corrosion to decrease the residual stress and then to optimize the microstructure when brazed to Nb. Thermal and electrochemical corrosion are conducted to diminish the SiC matrix and the interface between carbon fibers and SiC, respectively. The surface structure can be filled with brazing alloy characterized by the gradient layer of carbon fiber reinforced brazing alloy. Compared with thermal corrosion, SiC particles and nano Ti5Si3 are uniformly dispersed throughout the gradient layer in electrochemical corrosion. The layer decreases the difference in property consequently to relieve the residual stress. In addition, the original reaction layer will be replaced by this layer, favorable for the increase in joining strength and fracture toughness. The brittle facture at the reaction layer in original joints can be transformed into the zig-zag path. The shear strength of joints with the thermal and electrochemical corrosion depth of 100 μm increases to 151.6 MPa and 164.3 MPa, respectively, which is 77% and 92% higher than that of original joints.

Herein, binder-free hierarchically structured nickel cobalt sulfide nanoflakes on CoO nanosheets with the help of carbon layer (Ni-Co-S@C@CoO NAs) are fabricated via hydrothermal synthesis, carbonization treatment and electrodeposition, where three key components (CoO nanosheet arrays, a carbon layer and Ni-Co-S nanoflakes) are strategically combined to construct an efficient electrode for supercapacitors. The highly well-defined CoO nanosheets are utilized as ideal conductive scaffolds, where the conductivity is further improved by coating carbon layer, as well as the large electroactive surface area of Ni-Co-S nanoflakes. Furthermore, self-supported electrodes are directly grown on Ni foam without conductive additives or binders, which can effectively simplify the whole preparation process and achieve excellent electrical contact. Benefiting from the unique structural features, the hierarchically structured Ni-Co-S@C@CoO NAs exhibit high specific capacitance up to 4.97 F cm−2, excellent rate capability, and maintains 93.2% of the initial capacitance after 10000 cycles. Furthermore, an asymmetric supercapacitor using the Ni-Co-S@C@CoO NAs electrode and activated carbon is assembled, which achieves a high energy density (49.7 W h kg−1) with long cycling lifespan. These results demonstrate the as-fabricated Ni-Co-S@C@CoO NAs can be a competitive battery-like electrode for supercapacitors in energy storages.

Energy density of asymmetric supercapacitors (ASCs) is greatly limited by the electrochemical performance, especially low specific capacitance and poor cycling stability, of anode materials. To achieve high-performance ASCs, herein, we designed and synthesized a new anode material of Fe3O4 nanosheet arrays, which were encapsulated in situ by graphene layers (G@Fe3O4) through plasma enhanced chemical vapor deposition. Vertical-standing G@Fe3O4 nanosheet arrays directly on the conductive substrates can facilitate electrolyte diffusion and reduce the internal resistance. Furthermore, the highly conductive graphene layers in situ encapsulating the Fe3O4 nanosheets not only could provide fast ion and electron transport pathways, but could also maintain a stable structure for G@Fe3O4. When used as electrodes, G@Fe3O4 exhibited highest capacitance (up to 732 F g−1), better rate capability, and cycling stability as compared to pristine Fe3O4. Furthermore, an asymmetric supercapacitor device synthesized using G@Fe3O4 as an anode and CuCo2O4 as the cathode showed a high energy density of up to 82.8 W h kg−1 at a power density of 2047 W kg−1 and good cycling stability (88.3% capacitance after 10 000 cycles).

Herein, hierarchical CuCo2O4@NiMoO4 core–shell nanowire arrays were successfully synthesized on Ni foam via hydrothermal processes as a battery-like electrode. Owing to the unique core–shell structure and the synergetic effect from CuCo2O4 and NiMoO4, the resulting CuCo2O4@NiMoO4 core–shell arrays exhibit a high specific capacitance of 2207 F g−1 at 1.25 A g−1 and good rate capability with only about 4.4% capacitance loss after cycling tests. Furthermore, we assemble the corresponding asymmetric supercapacitor using CuCo2O4@NiMoO4 (positive electrode) and activated carbon (negative electrode), which delivers a high energy density (about 40 W h kg−1) and good cycle stability. Thereby, these electrochemical performances demonstrated that as-fabricated CuCo2O4@NiMoO4 core–shell arrays are promising candidates as electrodes for high-performance supercapacitors.

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 MoS2/NiS2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS2/NiS2 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.

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.

In article number 1700687, Junlei Qi, Jian Cao, and co‐workers report the development of vertical‐standing nanosized NiO encapsulated in graphene as electrodes for high‐performance supercapacitors. The resultant NiO encapsulated in high‐quality graphene layers as electrodes can exhibit a high specific capacity, good rate capability, and excellent cycling performance because of the integrated structures of NiO nanoparticles, the high‐quality graphene layers, and the vertical‐standing nanosheets.

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.