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The sucrose dehydrated by H2SO4 and composited with GO, followed by annealing in NH3/Ar at 800 °C, generates N-HC/rGO hybrid with more ultra-micropores, which makes the electrochemical performance of the hybrid better than hard carbon alone.

The thermal dispersion power depends on thermal conductivity and thickness of the thermal dispersion material that is a critical component of modern electronic devices due to the demands of high operating power in a miniaturized space. Films made of assembled graphene flakes have been becoming an emerging thermal dispersion material owing to their high thermal conductivity and tunable thickness up to millimeters, which outperform that of artificial graphite films made from polyimide. But the thermal conductivity typically decreases with the increase of film thickness. In our work, by pre-reducing the graphene oxide with Vitamin C and sequentially annealing the stacking films at 2950 °C, a 80 μm-thick graphene film (GF) with an in-plane thermal conductivity of above 1600 W/(m·K) is achieved. Detailed characterizations indicate that, the addition of Vitamin C is beneficial to the assembly ordering of graphene oxide platelets and the defect healing during the thermal annealing, which both contribute to the excellent thermal conductivity of the films. Our work provides an industrially scalable strategy towards high performance heat dissipation films for future electronic devices.

How do scientific ideas become market products? There is probably no single pathway for such transformation. And yet, there are certain similarities in the way how advanced materials evolve from laboratory studies to being used in technology. Common steps in such progress are the enhancement of useful properties, development of the production methods, creation of industrially-relevant modification of the material itself and its fabrication process. The reason in the emergent similarities in the pathway to market is the established relation between materials supplier and the final product manufacturers. A dramatic role in such relations is played by industrial standards. The later can help, but also, if incorrectly developed, can stumble the final product development. We will study the process of commercialisation of graphene, its transformation to commodity and the emerging graphene standardisation efforts.

Among many phase-changing materials, graphite is probably the most studied and interesting: the rhombohedral (3R) and hexagonal (2H) phases exhibit dramatically different electronic properties. However, up to now the only way to promote 3R to 2H phase transition is through exposure to elevated temperatures (above 1000 °C); thus, it is not feasible for modern technology. In this work, we demonstrate that 3R to 2H phase transition can be promoted by changing the charged state of 3D graphite, which promotes the repulsion between the layers and significantly reduces the energy barrier between the 3R and 2H phases. In particular, we show that charge transfer from lithium nitride (α-Li3N) to graphite can lower the transition temperature down to 350 °C. The proposed interlayer slipping model potentially offers the control over topological states at the interfaces between different phases, making this system even more attractive for future electronic applications.

In past decades, the performance of supercapacitors has been greatly improved by rationalizing the electrode materials at the nanoscale. However, there is still a lack of understanding on how the charges are efficiently stored in the electrodes or transported across the electrolyte/electrode interface. As it is very challenging to investigate the ion-involved physical and chemical processes with single experiment or computation, combining advanced analytic techniques with electrochemical measurements, i.e., developing in-situ characterizations, have shown considerable prospect for the better understanding of behaviors of ions in electrodes for supercapacitors. Herein, we briefly review several typical in-situ techniques and the mechanisms these techniques reveal in charge storage mechanisms specifically in supercapacitors. Possible strategies for designing better electrode materials are also discussed.

Graphite oxide has become an important precursor for graphene oxide, reduced graphene oxide, and a wide range of other graphene-based materials or composites. In numerous Hummers’ methods for the p...

Electrical double-layer capacitors are widely concerned for their high power density, long cycling life and high cycling efficiency. However, their wide application is limited by their low energy density. In this study, we propose a simple yet environmental friendly method to synthesize cobalt and nitrogen atoms co-doped porous carbon (CoAT-NC) material. Cobalt atoms connected with primarily pyridinic nitrogen atoms can be uniformly dispersed in the amorphous carbon matrix, which is benefit for improving electrical conductivity and density of states of the carbon material. Therefore, an enhanced performance is expected when CoAT-NC is served as electrode in a supercapacitor device. CoAT-NC displays a good gravimetric capacitance of 160 F/g at 0.5 A/g combing with outstanding capacitance retention of 90% at an extremely high current density of 100 A/g in acid electrolyte. Furthermore, a good energy density of 30 Wh/kg can be obtained in the organic electrolyte.

Recent experiments on magic-angle twisted bi-layer graphene have attracted intensive attention due to exotic properties such as unconventional superconductivity and correlated insulation. These phenomena were often found at a magic angle less than 1.1°. However, the preparation of precisely controlled bi-layer graphene with a small magic angle is challenging. In this work, electronic properties of large-angle twisted bi-layer graphene (TBG) under pressure are investigated with density functional theory. We demonstrate that large-angle TBG can display flat bands nearby the Fermi level under pressure, which may also induce interesting properties such as superconductivity which have only been found in small-angle TBG at ambient pressure. The Fermi velocity is found to decrease monotonously with pressure for large twisted angles, e.g., 21.8°. Our work indicates that applying pressure provides opportunities for flat-band engineering in larger angle TBG and supports further exploration in related investigations.

Acidic water electrolysis is of great importance for boosting the development of renewable energy. However, it severely suffers from the trade-off between high activity and long lifespan for oxygen evolution catalysts on the anode side. This is because the sluggish kinetics of oxygen evolution reaction necessitates the application of a high overpotential to achieve considerable current, which inevitably drives the catalysts far away from their thermodynamic equilibrium states. Here we demonstrate a new oxygen evolution model catalyst-hierarchical palladium (Pd) whose performance even surpasses the benchmark Ir- and Ru-based materials. The Pd catalyst displays an ultralow overpotential (196 mV), excellent durability and mitigated degradation (66 μV h−1) at 10 mA cm−2 in 1 M HClO4. Tensile strain on Pd (111) facets weakens the binding of oxygen species on electrochemical etching-derived hierarchical Pd and thereby leads to two orders of magnitudes of enhancement of mass activity in comparison to the parent Pd bulk materials. Furthermore, the Pd catalyst displays the bifunctional catalytic properties for both oxygen and hydrogen evolutions and can deliver a current density of 2 A cm–2 at a low cell voltage of 1.771 V when fabricated into polymer electrolyte membrane electrolyser.

Lightweight yet strong paper with high toughness is desirable especially for impact protection. Herein we demonstrated electrically conductive and mechanically robust paper (AP/PB-GP) made of reduced graphene oxide via interfacial crosslinking with 1-aminopyrene (AP) and 1-pyrenebutyrat (PB) small molecules. The AP/PB-GP with thickness of over ten micrometer delivers a record-high toughness (∼69.67 ± 15.3 MJ m−3 in average), simultaneously with superior strength (close to 1 GPa), allowing an impressive specific penetration energy absorption (∼0.17 MJ kg−1) at high impact velocities when used for ballistic impact protection. Detailed interfacial and structural analysis reveals that the reinforcement is synergistically determined by π-π interaction and H-bonding linkage between adjacent graphene lamellae. Especially, the defective pores within the graphene platelets benefit the favorable adsorption of the pyrene-containing molecules, which imperatively maximizes the interfacial binding, facilitating deflecting crack and plastic deformation under loading. Density functional theory simulation suggests that the coupling between the polar functional groups, e.g., −COOH, at the edges of graphene platelets and −NH2 and −COOH of AP/PB are critical to the formation of hydrogen bonding network.

Fe2O3 has become a promising anode material in lithium-ion batteries (LIBs) in light of its low cost, high theoretical capacity (1007 mA h g−1) and abundant reserves on the earth. Nevertheless, the practical application of Fe2O3 as the anode material in LIBs is greatly hindered by several severe issues, such as drastic capacity falloff, short cyclic life and huge volume change during the charge/discharge process. To tackle these limitations, carbon-coated Fe2O3 (Fe2O3@MOFC) composites with a hollow sea urchin nanostructure were prepared by an effective and controllable morphology-inherited strategy. Metal-organic framework (MOF)-coated FeOOH (FeOOH@-MIL-100(Fe)) was applied as the precursor and self-sacrificial template. During annealing, the outer MOF layer protected the structure of inner Fe2O3 from collapsing and converted to a carbon coating layer in situ. When applied as anode materials in LIBs, Fe2O3@MOFC composites showed an initial discharge capacity of 1366.9 mA h g−1 and a capacity preservation of 1551.3 mA h g−1 after 200 cycles at a current density of 0.1 A g−1. When increasing the current density to 1 A g−1, a reversible and high capacity of 1208.6 mA h g−1 was obtained. The enhanced electrochemical performance was attributed to the MOF-derived carbon coating layers and the unique hollow sea urchin nanostructures. They mitigated the effects of volume expansion, increased the lithium-ion mobility of electrode, and stabilized the as-formed solid electrolyte interphase films.

Many lithium (Li) metal anodes reported so far have been prepared by electrodeposition of Li on current collectors, for which sacrificing cells are needed in the practical applications. In this work, Li foils are compressed with various carbons such as reduced graphite oxide (rGO), activated microwave exfoliated GO (aMEGO) and activated carbon (AC) by rolling press, resulting in C/Li composites for Li metal anodes. The electrochemical evaluations show that all the three composite anodes are cyclable for 1500 h at a current density of 10 mA cm−2 for a capacity of 10 mA h cm−2. Specifically, the rGO/Li anode shows relatively lower overpotentials and more stable cycling performance than the other two. Characterizations indicate that the high pore volume and the moderate pore size of the rGO powder benefit the Li migration and the tolerance to volume change during Li plating/stripping, demonstrating a more stable electrode-electrolyte interface in the cycling. The study provides a potentially scalable and cost-effective strategy for the production of high-performance Li metal anodes.

The frozen section (FS) diagnoses of pathology experts are used in China to determine whether sentinel lymph nodes of breast cancer have metastasis during operation. Direct implementation of a deep neural network (DNN) in clinical practice may be hindered by misdiagnosis of the algorithm, which affects a patient's treatment decision. In this study, we first obtained the prediction result of the commonly used patch-DNN, then we present a relative risk classification and regression tree (RRCART) to identify the misdiagnosed whole-slide images (WSIs) and recommend them to be reviewed by pathologists. Applying this framework to 2362 WSIs of breast cancer lymph node metastasis, test on frozen section results in the mean area under the curve (AUC) reached 0.9851. However, the mean misdiagnosis rate (0.0248), was significantly higher than the pathologists’ misdiagnosis rate (p p > 0.01). However, the other low-accuracy group included most of the misdiagnoses of DNN models. Our research shows that the misdiagnosis from deep learning model can be further enriched by our method, and that the low-accuracy WSIs must be selected for pathologists to review and the high-accuracy ones may be ready for pathologists to give diagnostic reports.

In the past decade, flexible physical sensors have attracted great attention due to their wide applications in many emerging areas including health-monitoring, human-machine interfaces, smart robots, and entertainment. However, conventional sensors are typically designed to respond to a specific stimulus or a deformation along only one single axis, while directional tracking and accurate monitoring of complex multi-axis stimuli is more critical in practical applications. Multidimensional sensors with distinguishable signals for simultaneous detection of complex postures and movements in multiple directions are highly demanded for the development of wearable electronics. Recently, many efforts have been devoted to the design and fabrication of multidimensional sensors that are capable of distinguishing stimuli from different directions accurately. Benefiting from their unique decoupling mechanisms, anisotropic architectures have been proved to be promising structures for multidimensional sensing. This review summarizes the present state and advances of the design and preparation strategies for fabricating multidimensional sensors based on anisotropic conducting networks. The fabrication strategies of different anisotropic structures, the working mechanism of various types of multidimensional sensing and their corresponding unique applications are presented and discussed. The potential challenges faced by multidimensional sensors are revealed to provide an insightful outlook for the future development.

Oxygen evolution reaction (OER)-induced reconstruction on precatalysts generally results in surface-reconstructed catalysts with less active species and thus low mass activity. Herein, the deeply r...

Tremendous efforts have been dedicated to developing high-performance energy storage devices based on the micro- or nano-manipulation of novel carbon electrodes, as certain nanocarbons are perceived to have advantages such as high specific surface areas, superior electric conductivities, excellent mechanical properties and so on. In typical electrochemical electrodes, ions are intercalated/deintercalated into/from the bulk (for batteries) or adsorbed/desorbed on/from the surface (for electrochemical capacitors). Fast ionic transport, significantly determined by ionic channels in active electrodes or supporting materials, is a prerequisite for the efficient energy storage with carbons. In this report, we summarize recent design strategies for ionic channels in novel carbons and give comments on the promising features based on those carbons towards tailorable ionic channels.

Graphene oxide (GO) has demonstrated potential applications in various fields, and attracted intensive attention in industry as well. Numerous companies worldwide have been working on the industrial applications of GO-based materials in, e.g., thermal management, multifunctional composites, anti-corrosion paints, lubricants, energy storage, environment protection and biomedicals. This review presents a short summary on the proceedings of GO towards industrialization, including the large-scale production and some promising applications, by providing views on the processing strategies and challenges specifically for the industrial use of GO. This review would help the scientists in this area to find topics for overcoming challenges together with engineers.

Unique interfacial properties within heterostructures play vital roles in enhancing hydrogen evolution reaction (HER) electrocatalysis. On the basis of the MoO2-Ni heterostructure, we hereby propos...

Graphene oxide (GO) suspensions in solvents are the most important feedstocks for preparing GO based composites, and the dispersion state of GO on the microscale in solvent is a dominating factor in determining the physical properties of GO based composites. However, the morphology of GO sheets in solvents has hardly been reported due to the limitation of the characterization methods. Here, we report that the sheet thickness and lateral size of GO in solution can be identified using optical microscopy (OM) within a couple of minutes. The dispersion states of GO, including stretched flakes, scrolls, crumbles, and agglomerates, can also be distinguished. Moreover, the dispersion states, which change with the pH value and ionic strength of the solvent, are closely related to the dispersion stability of the GO suspension and the morphology of the GO/PVA composite. We believe that the fast observation and identification of GO sheets and their structural features in solvents, enabled by OM, opens up a new avenue to studying GO based composite materials in liquids.

The development of the basic understanding of the charge storage mechanisms in electrodes for energy storage applications needs deep characterization of the electrode/electrolyte interface. In this work, we studied the charge of the double layer capacitance at single layer graphene (SLG) electrode used as a model material, in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. The combination of electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance (EQCM) measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface. The capacitance is thus governed not only by the electronic properties of the graphene, but also by the specific organization of the electrolyte side at the SLG surface originating from the strong interactions existing between the EMIm+ cations and SLG surface. EQCM measurements also show that the carbon structure, with the presence of sp2 carbons, affects the charge storage mechanism by favoring counter‐ion adsorption on SLG electrode versus ion exchange mechanism in amorphous porous carbons., The charge of the double layer capacitance at a single layer graphene (SLG) electrode was studied in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. Electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface.

We perform femtosecond pump-probe spectroscopy to in situ investigate the ultrafast photocarrier dynamics in bilayer graphene and observe an acceleration of energy relaxation under pressure. In combination with in situ Raman spectroscopy and ab initio molecular dynamics simulations, we reveal that interlayer shear and breathing modes have significant contributions to the faster hot-carrier relaxations by coupling with the in-plane vibration modes under pressure. Our work suggests that further understanding the effect of interlayer interaction on the behaviors of electrons and phonons would be critical to tailor the photocarrier dynamic properties of bilayer graphene.

When used as a current collector, aluminum foil (AF) is vulnerable to local anodic corrosion during the charge/discharge process, which can lead to the deterioration of lithium-ion batteries (LIBs). Herein, a graphene foil (GF) with high electrical conductivity (∼5800 S cm-1) and low mass density (1.80 g cm-3) was prepared by reduction of graphene oxide foil with ultra-high temperature (2800 °C) annealing, and it exhibited significantly anodic corrosion resistance when serving as a current collector. Moreover, a LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode using GF as a current collector (NCM523/GF) demonstrated a gravimetric capacity of 137.3 mAh g-1 at 0.5 C based on the mass of the whole electrode consisting of the active material, carbon black, binder, and the current collector, which is 44.5% higher than that of the NCM523/AF electrode. Furthermore, the NCM523/GF electrode retains higher capacity at relatively faster rates, from 0.1 C to 5.0 C. Therefore, GF, a lightweight corrosion-resistant current collector, is expected to replace the current commercial metal current collectors in LIBs and to achieve high energy-density batteries.

Developing multicomponent transition-metal phosphides has become an efficient way to improve the capacitive performance of single-component transition-metal phosphides. However, reports on quaternary phosphides for supercapacitor applications are still scarce. Here, we report high capacity and energy density of Zn-Ni-Co-P quaternary phosphide nanowire arrays on nickel foam (ZNCP-NF) composed of highly conductive metal-rich phosphides as an advanced binder-free electrode in aqueous asymmetric supercapacitors. In a three-electrode system using the new electrode, a high specific capacity of 1111 C g

Graphite oxide and its exfoliated counterpart, graphene oxide, are important precursors for the large-scale production of graphene-based materials and many relevant applications. The current batch-style preparation of graphite oxide suffers from safety concern, long reaction time, and nonuniform product quality, due to the large volume of reactors and slow energy exchange. Reaction in microchannels can largely enhance the oxidization efficiency of graphite due to the enhanced mass transfer and extremely quick energy exchange, by which the controllable oxidization of graphite is achieved in ≈2 min. Comprehensive characterizations show that the graphene oxide obtained through the microfluidic strategy has features like those prepared in laboratory beakers and industrial reactors, yet with the higher oxidization degree and more epoxy groups. More importantly, the microfluidic preparation allows for on-line monitoring of the oxidization by Raman spectroscopy, ready for the dynamical control of reaction condition and product quality. The capability of continuous preparation is also demonstrated by showing the assembly of fibers and reduction of graphene oxide in microfluidic channels, and the applicability of graphene oxide prepared from the microfluidic strategy for thermally and electrically conductive films.

从氧化石墨中获得石墨烯材料在负载金属催化剂中具有很大的应用潜力, 但在通过化学气相沉积制备的高质量石墨烯(CVDG)上 均匀负载金属纳米粒子仍然是一个挑战. 我们成功制备了在CVDG上均匀负载具有约3.3 nm尺寸的铂纳米粒子的超薄复合薄膜(Pt-CVDG), 并且这种薄膜可通过类似CVDG转移的方法转移到目标衬底上. Pt-CVDG薄膜在甲醇催化氧化中表现出优异的性能, 具有高达 94.1 m2 g−1Pt的电化学活性表面积, 并且在0.7 V下具有293.1 mA mg−1 Pt的高质量活性电流密度, 该电流密度几乎是相同条件下商业Pt/C的 两倍. 此外, 为进一步提高催化性能, 将钌沉积到Pt-CVDG薄膜上, 在Ru覆盖率达到50%时得到比原始样品高2倍的催化电流密度且催化起始电位降低0.2 V. 同时这种基于CVDG的复合薄膜为评估Pt NPs-碳杂化催化剂性能的极限提供了一个简单模型.

Activated carbon derived from plant wastes is attractive for the fabrication of low cost and high performance electrochemical energy storage devices. The heteroatoms (O, N)-doped porous carbon (KAC-700) is fabricated from bamboo shoots shells via KOH activation. The symmetric supercapacitor based on KAC-700 has gravimetric and volumetric capacitance of 223.21 F g−1 and 167.63 F cm−3, respectively, at current density of 1 A g−1 in 1 M H2SO4 electrolyte. This supercapacitor also delivers a high energy density of 13.15 Wh kg−1 at power density of 546.60 W kg−1 in 1 M Na2SO4 electrolyte, as well as high capacitance retention rate of 93.62% after 4000 cycles at 5 A g−1. Compared with graphene, carbon nanotubes and other expensive carbon material, this activated carbon has a bright future due to its low cost and easy fabrication process as electrode material for supercapacitors.

The electrocatalytic hydrogen evolution reaction (HER) performance of carbon-coated β-NiS (NiS@C) nanocrystals has been investigated for the first time. The NiS@C nanocrystals were synthesized via a facile solvothermal method followed by in-situ carbonization process with the solvent (ethylene glycol) as the carbon source. Benefited from the well-dispersed NiS nanocrystals and the formation of carbon layer on NiS nanocrystals, the NiS@C nanocrystals displayed a high HER activity in 0.5 M H2SO4, which needed an overpotential of 85 mV to achieve current density of 10 mA cm−1 with a Tafel slope of 46 mV dec−1, as well as long term stability for HER. Additionally, the NiS@C nanocrystals also showed efficient electrocatalytic activity under alkaline media.

Novel bowl-like, apple-like, and spherical PdCu alloy hollow microparticles with mesoporous nanoshells are synthesized through a simple disproportionation reaction route using a spherical Cu2O template with increasing H2PdCl4 ratio. The diameter of hollow particles is about 1 μm, and the thickness of mesoporous shells is about 50 nm. The obtained bowl-like PdCu alloy hollow microparticles with mesoporous nanoshells exhibit the highest electrocatalytic activity among the apple-like and spherical PdCu hollow microparticles and commercial Pd/C electrocatalysts toward methanol anodic oxidation for fuel cells. The remarkably excellent electrocatalytic performance of bowl-like PdCu alloy electrocatalysts might be attributed to the unique bowl-like hollow architecture with highly mesoporous nanoshells which are constructed by self-supported PdCu nanoparticles. The strategy presented here might help pave the way for the synthesis of novel nano-/microcomplex hollow materials with mesoporous nanoshells.

Paper-based flexible supercapacitors (SCs) show advantages due to the improved adhesion between paper and active materials, the simplified printing process and the lower cost, compared to other substrates such as plastics. Here we report the fabrication of solid-state yet flexible SCs by inkjet-printing a hybrid ink consisting of carbon quantum dots (CQDs) and graphene oxide (GO) platelets, followed by casting of polyvinyl alcohol (PVA)/sulfuric acid (H2SO4) gel electrolyte. The SC obtained from 100-time-printing of the hybrid ink shows a specific capacitance of ~1.0 mF cm−2 at a scan rate of 100 mV s−1, which is enhanced by nearly 150%; the whole device including paper substrate, gel electrolyte and active material demonstrates an energy density of 0.078 mW h cm−3 at a power density of 0.28 mW cm−3. In addition, the excellent mechanical strength of GO platelets ensures the good flexibility and mechanical robustness of the printed SCs, which show a retention of 98% in capacitance after being bended for 1,000 cycles at a bending radius of 7.6 mm. This study demonstrates a promising strategy for the large-scale preparation of low-cost, lightweight, and flexible/wearable energy storage devices based on carbon-based ink and paper substrate.

In this work, we utilized a facile air oxidative dealloying approach to synthesize PtCu hierarchical branched nanodendrites (HBNDs). The systematical investigation on the morphology, composition, and structure of PtCu HBNDs by various techniques demonstrates they are three-dimensional open porous nanostructures. The PtCu HBNDs show composition-dependent catalysis in hydrogen evolution reaction (HER). The Pt1Cu1.03-D with average size about 40 nm composed of integrated ultrathin branches, presents the highest HER activity with only 20 mV overpotential to achieve 10 mA/cm2, 19.34 A/mgPt and 9.64 mA/cm2 in mass and specific activity at −0.2 V, and excellent durability. The superior HER activity is attributed to the unique porous dendritic structure and electronic synergistic interactions between Pt and Cu as indicated by X-ray photoelectron spectroscopy and density functional theory calculation. This work opens up a new facile route to design large accessible surface and high-performance electrocatalysts with low utilization of Pt for electrochemical energy conversion.

Graphite made from graphite oxide with well-defined basal plane (perpendicular to the c-axis or stacking orientation) and cross-sectional edges (along to the stacking orientation) are utilized to investigate the field emission characteristics. The significant differences of basal plane and edges from the same graphite sample are characterized. It is found that the basal plane with wrinkles has lower turn-on field (5.01 V/μm, corresponding to a current of 10 μA/cm2) and threshold field (7.38 V/μm, corresponding to current of 1 mA/cm2), compared to the edges. Fowler-Nordheim (FN) analysis indicates that the basal plane has larger field enhanced factor (1374, while 453 for edges), but smaller emission area efficiency (1.24 × 10−3) than the edges (0.526). Characterizations show that the sparse wrinkles on the basal plane play important roles as emission sites; the oxygen-containing groups which tend to form on the edges lead to an increase in work function and the deterioration in field emission performance.

The plant waste pomelo peels are used as carbon precursors to fabricate nitrogen-doped hierarchical porous carbon. The sample PC600 is fabricated at mild calcination temperature of 600 °C, which has nitrogen content of as high as 4.47% and hierarchical pores with a BET surface area of 1104 m2 g−1. The symmetric supercapacitor based on PC600//PC600 electrodes exhibits excellent electrochemical performance benefiting from both the electric double-layer capacitance and pseudocapacitance of PC600. In 1 M H2SO4 electrolyte, this supercapacitor delivers gravimetric capacitance of 208.7 F g−1, volumetric capacitance of 219.3 F cm−3, and energy density of 7.3 Wh kg−1 at a current density of 1 A g−1. Furthermore, the extraordinary energy density of 21.6 Wh kg−1 at 1 A g−1 and 17.1 Wh kg−1 at 20 A g−1 are obtained in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. The suitable calcination process can make the contents of nitrogen atoms and pores structures in PC600 to achieve an optimal combination, leading to improved electrochemical performance.

Highly active, durable and cost-effective eletrocatalysts are crucial for hydrogen evolution reaction (HER). Herein, we report novel hollow hybrid spheres comprising of amorphous Ni(OH)2 and crystalline CuS mesoporous nano-shelled heterostructures as efficient HER electrocatalysts. Spherical Cu2O particles are used as templates for fabrication of Ni(OH)2@CuS hollow spheres with nano-shelled heterostructures. The as-obtained catalysts exhibit much higher performance than the single Ni(OH)2, CuS, their physical mixture and crystalline Ni(OH)2@CuS toward water electrochemical reduction in alkaline medium. The superior HER electrocatalytic performance might be attributed to the unique hollow mesoporous nanoshelled architecture and the heterostructured synergetic effects between amorphous Ni(OH)2 and crystalline CuS, in which the short-range order of the inner amorphous Ni(OH)2 mesoporous shell creates abundant active sites on the surface, and the conductive CuS out layer promotes electron transportation. This work might open a door for designing and synthesizing of hollow nanomaterials with mesoporous nano-shelled heterostructures consist of amorphous and crystalline phase for applications in electrochemical catalysis and energy conversion.

The hydrogen adsorption strength and activity of each catalytic site greatly influence the hydrogen evolution reaction (HER) kinetics of electrocatalysts. It remains a challenge to effectively activate catalytic sites for interfacial carbon-catalyzed electrocatalysts. Here, we report a polyoxomolybdate-derived carbon-encapsulated multicomponent catalyst with nanowire structure. The activation of catalytic sites and enhancement of HER kinetics are achieved by incorporating tiny MoO2 and Ni nanoparticles into a N-doped carbon layer (denoted as MoO2–Ni@NC). The MoO2–Ni@NC catalyst possesses a remarkable HER activity and is superior to most carbon-encapsulated electrocatalysts. In particular, it achieves a low overpotential of 58 mV at −10 mA cm−2, and a high exchange current density of 0.375 mA cm−2 with good stability (up to 80 000 s) in 0.5 M H2SO4. Theoretical analyses suggest that the N-doped carbon layer acts as an active adsorption site for hydrogen. The inner MoO2–Ni species behave as effective promoters to synergistically modulate the hydrogen adsorption strength on the interfacial carbon and enable the active sites to be more efficient. The synthesis strategy and the revealed catalytic mechanism can guide the rational design of high-efficiency carbon-encapsulated HER electrocatalysts.