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The progress of flexible/wearable electronic devices with multi-functionality has stimulated the rapid development of the matching power supply devices. Flexible supercapacitors with high electrochemical performance and mechanical flexibility are considered as attractive technologies to power flexible electronics and have been studied intensively. Carbon nanomaterials, such as carbon nanotube, graphene, and their composites, possess unprecedented physical/chemical properties and exhibit great potential for use in flexible supercapacitors. In this review, the recent progress of state-of-the-art flexible supercapacitors using advanced carbon nanomaterials is expounded comprehensively and systematically, the topic covered the micro/nano-structure control, macroscopic morphologies design, property optimization and application of carbon nanomaterials. Based on the current advances, the challenges and prospects of carbon nanomaterials applied in flexible supercapacitors are outlined and highlighted. As last, the matching between the characters of carbon nanomaterials, construction of flexible supercapacitors and fabrication technologies are put forward.

Based on the tungsten hydrate structure model, we report the strategy to fabricate hierarchically structured WO3·0.33H2O/graphene composites through a facile hydrothermal approach. The structure characteristics, conversion reaction mechanism as well as the electrochemical properties are carefully investigated. The hierarchical architectures assembled by nanorods or nanobricks of about 20 nm thickness combine the advantages of reduced length scale of Li ion diffusion derived from nanosizes and structural stability guaranteed by hierarchical features. In addition, compared with bare WO3·0.33H2O and anhydrous WO3, the WO3·0.33H2O/graphene composites exhibit the optimal performances with high rate capability and good cycle stability, which is attributed to synergistic effects of structural hydration and graphene: providing a more open charge transfer channel, forming a conductive pathway and accommodating the volume change. Such an improved lithium storage performance makes the graphene-based WO3·0.33H2O a promising anode candidate for lithium-ion battery applications.

Tungsten carbide (WC) particles-embedded carbon nanomaterials with ultrathin edges and high degree of graphitization are very favorable co-catalysts for Pt in electrochemical fields. Herein, WC-embedded graphite carbon films (WC@GCFs) were successfully fabricated as co-catalysts for hydrogen evolution reaction (HER) via an in-situ carbonization technique. The mass specific activity of the WC@GCFs loading Pt NPs is 278 mA mg−1 Pt and 277 mA mg−1 Pt under the overpotential of 48 and 52 mV, which is 1.3 and 1.45 times higher than those of the commercial Pt-C (212.8 mA mg−1 Pt and 191.4 mA mg−1 Pt). The WC@GCFs-Pt displays excellent high stability for HER in acidic and alkaline media even after 5000 potential cycles. As expected, the GCFs originated from the surface of WC can effectively prevent WC particles from agglomeration, which contributes to high catalytic activity and stability of WC. The in-situ formed GCFs possesses ultrathin edges (~5 carbon layers), high degree of graphitization, and some oxygen-containing function groups. Charges are easily transferred from Pt NPs to WC via the linked-GCFs, which contributes to the high HER activity of WC@GCFs-Pt. We believe this work can provide a more economical and efficient route for large-scale synthesis of graphite carbon films coated transition metal carbide as co-catalysts in electrochemical fields.

A new pseudocapacitive nanocomposite is reported in this article. Such amorphous materials were prepared via restacking of Ni-Mn LDH and MnO2 nanosheets obtained by exfoliation treatments. Synergetic effects of the two components were demonstrated in both alkaline and neutral aqueous electrolytes, as rate capability and cycle stability were both greatly improved compared to each-component samples and mixture. Tests on an activated carbon//nano-composite asymmetric device reveal that the energy density could be about 16 Wh/Kg at a power density of 15 KW/Kg in alkaline electrolytes, while in neutral electrolytes, the value reached about 13 Wh/Kg at a power density of 9 KW/Kg, matching with many other composition technologies. Besides, rather small leakage and self-discharge currents further indicate its promising applications in practical areas.

The common one dimensional (1D) core-shell phase junction usually cannot fully utilize the separated charges because one phase is encapsulated inside, which leads to the incomplete release of the electrons or holes. Here, a unique vertical 1D/1D tungsten oxide phase junction constructed by orthorhombic WO3·0.33H2O (o-WO3·0.33H2O) nanorods and hexagonal WO3 (h-WO3) nanowires in the sunflower-like structure was fabricated via a facile one-step hydrothermal method. The nanorods and the nanowires vertically intersect at the endpoint to construct the vertical 1D/1D phase junction with another end exposed outside. This structure ensures that both two phases can contact the pollutants, so as to fully release the holes and electrons that accumulate on the o-WO3·0.33H2O and h-WO3 phase, respectively. Furthermore, the two phases are both single crystals, substantially decreasing the impediments of defects to the transport of the photogenerated charges. This novel hierarchical structure with vertical 1D o-WO3·0.33H2O/h-WO3 phase junction can significantly improve the utilization efficiency of the separated photogenerated charges and thus effectively enhance the photocatalytic performance.

It is known that the exposed facet and defect state are crucial to the photocatalytic performance. Here, we report that the exposed facets of the building blocks in the tungsten oxide hierarchical nanostructures could be controlled by adjusting the amount of formamide in the hydrothermal precursor solution and the oxygen vacancies were successfully introduced through the post-air annealing. It is found that exposing high percentage (020) facet is unbeneficial for the photocatalytic performance and (200) and (002) facets should be the photocatalytic active facets of the hexagonal tungsten oxide. The hexagonal tungsten oxide with oxygen vacancies and maximum (200) and (002) facets archives highest photocatalytic performance in degrading rhodamine B under simulated solar light irradiation, which the rate constant per specific surface area (k/SBET) is 7.3 times as high as the sample without oxygen vacancies and minimum (200) and (002) facets. Both introducing oxygen vacancies and exposing (200) and (002) facets can enhance the separation efficiency of photo-generated charges, thus improving the photocatalytic performance.

A unique reduced graphene oxide (RGO) three-dimensionally wrapped WO 3 (WO 3 @RGO) composite was synthesized via a facile one-step hydrothermal method. In this composite, the building blocks of the WO 3 hierarchical structure, the nanobelts, were intimately wrapped by a layer of RGO. Due to the synergistic effect of the hierarchical structure of WO 3 and intimately wrapped RGO on the surface of the nanobelts, the WO 3 @RGO showed much higher photocatalytic performance in degrading rhodamine B and phenol under simulated solar light irradiation than the bare WO 3 and other composites in which only the mainframe of WO 3 was wrapped by RGO. Moreover, the photocatalytic activity was significantly influenced by the loading amount of RGO. The optimal performance was found in the 1.2% WO 3 @RGO, which was about 2.50 times that of the bare WO 3 . Conclusively, using graphene to wrap the building blocks rather than only the mainframe of semiconductors is anticipated to be a promising method to achieve high-performance photocatalysts for solar energy conversion.

Highly graphitic carbon nanomaterials with large specific surface area and good dispersion are very favorable supports for Pt-based catalysts in fuel cells. Ultrathin and coiled carbon nanosheets (UC-CNS) were successfully synthesized via chemical vapor deposition method using tungsten carbide (WC) as substrate. After the WC@UC-CNS was immersed in HF/HNO3/H2O solution, UC-CNS was completely stripped away from the WC substrate without obvious destruction, and possessed coiled edges and more oxygen-containing functional groups for anchoring Pt nanoparticles. Another obtained product (WO3) could be used as a tungsten source to produce UC-CNS repeatedly. The purified UC-CNS, with thicknesses of 3.45–5.61 nm, possessed high specific surface area (547 m2 g−1) and high degree of graphitization (IG/ID=1.43). Pt loaded on the UC-CNS exhibited high electrocatalytic activity and extremely high stability for methanol oxidation reaction even after 14,000 potential cycles. We believe UC-CNS can be widely used in fuel cells and other related green chemical applications.

Supercapacitors based on commercialized metallic collectors (such as Cu and Al) possess an innate interface imperfection, causing long ion diffusion pathway and sluggish electron conduction, as well as inferior flexibility. Herein, we explore carbon nanotubes macroscopic films (CMF) as current collectors to build near-integrated electrodes via anchored combination between CMF and commercial active carbon (AC). In addition, our fabricated CMF presents outstanding electrolyte permeation, which shortens the ion diffusion pathway, increases the electron conduction and ameliorates the flexibility. As a result, the supercapacitor based on CMF exhibits prominent electrochemical performance of specific capacitance (48.5 F cm−3 at 0.5 A g−1), rate capability (82.5% from 0.5 to 16 A g−1) and volumetric energy density (104.9 Wh L−1), which higher than those of reported flexible supercapacitors. More importantly, the supercapacitor exhibits remarkable stability under different folding conditions, even in particular circumstances (such as low temperature and negative pressure). Further, the supercapacitors show good energy features in parallels and series. Therefore, it is believed that these supercapacitors based on CMF are promising in the future wearable energy storage devices in different operating environments.

The morphology of tungsten oxide (WO3) was effectively mediated by carbon nanotubes (CNTs) as templates. The grown direction of WO3 on the CNT bundle surfaces could be controlled, which mainly depended on the distribution state of tungsten acid (H2WO4) precursor in the reaction system. After thermal treatment of H2WO4/CNTs under nitrogen gas flow, WO3 with different morphologies (plates, short rods, and long rods) and sizes (10–1000 nm) supported by CNT bundles were finally obtained. The results indicated CNT bundles as templates can play an important role in regulating the morphologies of WO3. Moreover, the study shows that CNT bundles exhibit excellent prospects in the tailor-synthesis of micro/nanostructured materials with different dimensions. According to the peak current density for the 1000th electrochemical cycle in 0.5 mol L−1 H2SO4 and 0.5 mol L−1 CH3OH electrolyte solution, short rod-like WO3/CNTs exhibited higher peak current density (43.2 mA cm−2) than long rod-like WO3/CNTs (23.68 mA cm−2), plate-like WO3/CNTs (15.63 mA cm−2), CNTs (2.25 mA cm−2), and commercial WO3 (3.19 mA cm−2). The results demonstrated the potential application of short rod-like WO3/CNTs materials for hydrogen oxidation reaction of methanol fuel cells and in other related fields.

Tungsten carbide was prepared via a one step method, made from the compound of carbon black and tungstic acid. The tungsten precursor with small size was supported on carbon nanotubes as template, while H 2 and N 2 were used for providing deoxidization and protection atmosphere. In addition, two key conditions of atmosphere and temperature were investigated. The results show, if the reaction temperature is higher than 800 °C, and before H 2 and N 2 pass through the reaction tube which was in vacuum state, WO 3 can be carbonized into W, and then carbonized into W 2 C, and W 2 C further carbonized into WC. The method can realize the production of tungsten carbide with controllable morphology and low cost.

Low cycle fatigue test of AZ91D+0.3%Ce alloy was carried out in tension-compression symmetric cycle at room temperature, with triangular waveform-loading frequence in 1Hz and equivalent strain amplitude varied from 0.2% to 1.2% .The fatigue fracture morphology of the alloy was observed by SEM. The results indicate that the σ-ɛ hysteresis loops of AZ91D+0.3%Ce magnesium alloy exhibit some behaviors such as inflexion, asymmetry of tension and compression and serrated flow deformation at the higher total strain amplitudes; Fatigue life of AZ91D+Ce alloy is decreased with the increase of the equivalent strain amplitude, confirming to the equation of the Manson-Coffin;The behaviors of cyclic stress response and stress-strain of magnesium alloy mainly show cyclic strain hardening; Fatigue fracture of all the magnesium alloys exists several fatigue source zones, as the strain amplitude increases, the fracture surface becomes more rough and concavo-convex.