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While manganese-based cathodes have been intensively studied for zinc-ion batteries (ZIBs), the limited rate capability and cycle life have always been a difficult problem to be solved. Here, we report a mixed valent manganese oxide (MnOx) cathode with superior electrochemical performance, which exhibits a high specific capacity of 450 mA h/g at 0.2 C and a satisfactory specific capacity of 158.3 mA h/g at a high rate of 5 C. The mixed cathode system reduces the charge transfer resistance, and show good surface stability and adsorption properties, so it is beneficial for the storage of Zn2+. Meanwhile, coaxial fiber ZIBs (CFZIBs) with splendid flexibility are assembled utilizing the elaborately prepared cathode material. The CFZIBs achieve a reversible capacity of 255.8 mA h/g and the capacity retention rate is as high as 80 % after 1000 bending deformations. This study provides new opportunities for designing ZIBs with high performance and high flexibility.

Molybdenum disulfide (MoS2) has become one of the most promising non-platinum-based electrocatalysts for the hydrogen evolution reaction (HER) because of its unique layered structure. However, the catalytic performance of the thermodynamically stable MoS2 is hindered by its poor conductivity and scarce active sites. We developed a 3D porous N-doped graphene derivative-integrated metal-semiconductor (1T-2H) mixed phase MoS2 (MNG) using urea as a doping reagent. The highly exposed active sites were achieved by inducing the phase transition of MoS2 from 2H phase to 1T phase and the inclusion of highly N-incorporated reduced graphene oxide, both of which were simultaneously realized by optimizing the concentration of the doping reagent. Moreover, the charge/proton transfer was enhanced by the well-designed porous architecture and hydrophilic 1T-MoS2. With these advantages, the optimized MNG-40 catalyst has a small overpotential of 157 mV at a cathodic current density of 10 mA cm-2, a relatively low Tafel slope of 45.8 mV dec-1, and an excellent stability. This work represents a new strategy to design higher-performance HER catalysts and provides new insights into the structural regulation of metal composite transitions.

Owing to the superiority of high-power density and excellent cycling stability, supercapacitors (SCs) have been expected to substitute for secondary batteries as the desired orientation selected for energy storage devices. The incorporation of various heteroatoms into carbon-based materials via surface functionalization or doping technique has been considered as a significant way to ameliorate its properties for SCs application. In this review, a wide variety of fluorine-doped/fluorinated carbon-based materials are put together to overview the development path, preparation route and areas of application in detail. We critically review the optimization effect in electrochemical performance induced by the participation of fluorine element. Moreover, compared with large-scale energy storage devices, miniaturization, flexibility and planarization are an emerging development tendency of SCs. Fluorine-doped/fluorinated carbon-based materials hold great promise in the future.

International audience; In this paper, porous partially fluorinated graphene (PFG) for supercapacitors (SCs) was fabricated by a mild and secure one-pot hydrothermal method utilizing weakly coordinating anion BF4− as the fluorine source. The hydrolysis rate of sodium fluoroborate was adjusted by controlling the reaction temperature and PFG containing semi-ionic Csingle bondF bonds was obtained, where the content of semi-ionic Csingle bondF bonds in PFG can be easily regulated. The final experimental results show that the incorporation of fluorine not only modulates the electrochemical properties of the material, but also creates abundant pores. When assembled in a symmetric supercapacitor, the PFG shows a high specific capacitance of 269.7 F g−1 at 1 A g−1 and a superior rate capability with 89.3% capacitance retained, as the current density is increased from 1 A g−1 even to 20 A g−1. Furthermore, the resultant energy density for PFG is 9.4 Wh kg−1 at a power density of 250.0 W kg−1 (1 A g−1). All these results confirm that as-prepared partially fluorinated graphene is appropriate for the application in SCs and mass production.

In recent years, graphene oxide (GO), prepared by the modified Hummers’ method, and its derivatives have become a focus of research owing to their outstanding physical and chemical properties and low cost. Drawing inspiration from the mussel protein, a facile and environmentally-friendly method was employed to fabricate superhydrophobic/superoleophilic reduced graphene oxide (rGO) derivative. The preparation comprises two steps: coating GO nanosheets with polydopamine (PDA) and subsequent reaction with 1 H ,1 H ,2 H ,2 H -perfluorodecanethiol. Due to the excellent adhesive ability of PDA, the resulting f PDA modified rGO nanosheets (rGO- f PDA) were firmly immobilized onto polyurethane (PU) sponge skeleton by a simple drop-coating method. The as-prepared rGO- f PDA functionalized sponge exhibited superhydrophobic behavior with a water contact angle of 162°±2°, high organic adsorption capacity, recyclability and stable oil/water separation behavior under different acidic/alkaline conditions. Due to its facile fabrication technique and outstanding properties, the superhydrophobic-superoleophilic PU-rGO- f PDA sponge holds great promise as an oil adsorbent for cleaning up large-scale pollution of oil and organic solvents, and dehydrating crude oil.

Molybdenum disulfide (MoS

International audience; MnO2/MnO cathode material with superior Zn2+ storage performance is prepared through a simple physical mixing method. The MnO2/MnO nanocomposite with a mixed mass ratio of 12:1 exhibits the highest specific capacity (364.2 mA.h/g at 0.2C), good cycle performance (170.4 mA.h/g after 100 cycles) and excellent rate performance (205.7 mA.h/g at 2C). Analysis of cyclic voltammetry (CV) data at various scan rates shows that both diffusion-controlled insertion behavior and surface capacitive behavior contribute to the Zn2+ storage performance of MnO2/MnO cathodes. And the capacitive behavior contributes more at high discharge rates, due to the short paths of ion diffusion and the rapid transfer of electrons.

Highlights The traditional and novel etching methods are summarized and compared, especially fluorine-free method. The methods for accelerating exfoliation of Ti3C2Tx are classified.The energy storage mechanisms of Ti3C2Tx in different electrolytes are compared. Based on energy storage mechanisms, the influencing factors of morphology and surface functional groups are discussed.In response to the problems of the Ti3C2Tx, strategies for improving capacitance from structure modulation to composite structure construction are summarized and compared., Ti3C2Tx, a novel two-dimensional layer material, is widely used as electrode materials of supercapacitor due to its good metal conductivity, redox reaction active surface, and so on. However, there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance, such as restacking, re-crushing, and oxidation of titanium. Recently, many advances have been proposed to enhance capacitance performance of Ti3C2Tx. In this review, recent strategies for improving specific capacitance are summarized and compared, for example, film formation, surface modification, and composite method. Furthermore, in order to comprehend the mechanism of those efforts, this review analyzes the energy storage performance in different electrolytes and influencing factors. This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors.

Flexible supercapacitors have advanced rapidly in recent years and contributed to the development of wearable electronics. However, the operating temperature of the flexible supercapacitors usually falls within a narrow range, because of the constraints of the electrode materials and the electrolytes. Here, we report a flexible supercapacitor that can operate at extreme temperatures (down to −40 °C and up to 200 °C) with excellent electrochemical property and high durability. This device allows a maximum area specific capacitance of 330 mF/cm2. It has 2 F/cm3 volume specific capacitance and 1.7 mWh/cm3 energy density. The high stability of this supercapacitor enables 90% capacitance retention after 105 cycles. Moreover, deformation at extreme temperature does not reduce its energy storage ability.

Hydrogen production from water splitting has been considered as an effective and sustainable method to solve future energy related crisis. Molybdenum sulfides (e.g., MoS2) show promising catalytic ability in hydrogen evolution reaction (HER). Combining MoS2 with conductive carbon-based materials has aroused tremendous research interest recently. In this work, a highly efficient multiple-catalyst is developed for HER by decorating Pt nanoparticles (Pt NPs) on MoS2@graphene protected nickel woven fabrics (NiWF) substrate, which comprises the following components: (i) Graphene protected NiWF acts as the underlying substrate, supporting the whole structure; (ii) MoS2 nanoplates serve as a central and essential photosensitive component, forming a heterostructure with graphene simultaneously; and (iii) on the basis of the intrinsic photoluminescence effect of MoS2, together with the photoelectric response at the MoS2/graphene interface, Pt NPs are successfully deposited on the whole structure under illumination. Particularly and foremost, this work emphasizes on discussion and verification of the underlying mechanism for photopromoted electroless Pt NPs deposition. Due to this assembly approach, the usage amount of Pt is controlled at ∼5 wt % (∼0.59 at. %) with respect to the whole catalyst. MoS2@Substrate with Pt NPs deposited under 643 nm illumination, with the synergistic effect of MoS2 active sites and Pt NPs, demonstrates the most superior electrocatalytic performance, with negligible overpotential and low Tafel slope of 39.4 mV/dec.

Advanced materials with special wettability have attracted wide attention for their potential application in environmental remediation, catalysis or superfluid now. This contribution reports a straightforward and low-cost high-performance methodology for the preparation of carbon fiber felt with selective superwettability and fire resistance. The functionalized carbon fiber felt (UV-CFF) is prepared by a simple UV-O3 treatment process for the enhancement of its superamphiphilicity in air and superoleophobicity underwater, the underwater contact angles of the organics is over 155°. Subsequently, surface functionalization of UV-CFF with 4-trifluoromethyldiazobenzene hydrochloride is carried out. Its surface could be effectively modified with aryl and carbon–fluorine groups through diazonium chemistry to obtain a superhydrophobic carbon fiber felt (f-CFF) with water contact angle of 152.5 ± 0.8°. Both of the UV-CFF and f-CFF samples exhibits effective oil/water separation behavior. Benefiting from the selective superwettability, the two samples provide the potential to selectively eliminate underwater oily phases and emulsions under different hydraulic pressures. For UV-CFF, its rejection of oil reaches 100%, and the rejection of water for f-CFF reaches 98.21 ± 0.7%. The adsorption capacities of different types of organic solvents for f-CFF is 4–14 g g−1, and its demulsification capacity can reach to 99.9%. Due to its corrosion resistance, facile fabrication technique, cycle stability and flame retardancy, the carbon felts hold great promise for potential applications in environmental remediation of water.

With the prospect of growing popularity of portable electronic devices, there is a rising sense of urgency around the development of energy storage devices, such as supercapacitors and Li ion batteries. The properties of energy storage devices can be improved by the structure engineering of electrode materials, device design of cells, and performance optimization of systems. In this chapter, the applications of graphene in flexible supercapacitors and Li ion batteries are discussed, with the focus on materials fabrication, processing technology, and device design.

A dynamically stretchable solid state supercapacitor using graphene woven fabric (GWF) as electrode materials is designed and evaluated. The electrode is developed after GWF film is transferred onto a pre-stretched polymer substrate. Polyaniline is deposited covering the GWF film through in-situ electropolymerization to improve the electrochemical properties of the electrode. The supercapacitor is assembled in sandwich structure and packaged in polymer and its electrochemical performance is investigated under both static and dynamic stretching modes. The stretchable supercapacitors possess excellent static and dynamic stretchability. The dynamic strain can be up to 30% with excellent galvanic stability even under high strain rates (up to 60%/s).

A wearable and high-precision sensor for sound signal acquisition and recognition was fabricated from thin films of specially designed graphene woven fabrics (GWFs). Upon being stretched, a high density of random cracks appears in the network, which decreases the current pathways, thereby increasing the resistance. Therefore, the film could act as a strain sensor on the human throat in order to measure one’s speech through muscle movement, regardless of whether or not a sound is produced. The ultra-high sensitivity allows for the realization of rapid and low-frequency speech sampling by extracting the signature characteristics of sound waves. In this study, representative signals of 26 English letters, typical Chinese characters and tones, and even phrases and sentences were tested, revealing obvious and characteristic changes in resistance. Furthermore, resistance changes of the graphene sensor responded perfectly with pre-recorded sounds. By combining artificial intelligence with digital signal processing, we expect that, in the future, this graphene sensor will be able to successfully negotiate complex acoustic systems and large quantities of audio data.

Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%–80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials.

Graphene/Si has been proved to form a quality Schottky junction with high photoelectric conversion efficiency at AM 1.5. However, for the ultraviolet portion of the incident light, the photoelectric performance will degrade significantly due to severe absorption and recombination at the front surface. Herein, to realize enhanced ultraviolet detection with a graphene/Si diode, TiO2 nanoparticles (NPs, 3–5 nm) are synthesized and spin-coated on the graphene surface to improve the photoresponse in the ultraviolet region. According to our results, the conversion efficiency of the graphene/Si diode at 420 nm and 350 nm increases by 72.7% and 100% respectively with TiO2 coating. Then C−2–V measurements of both TiO2 and graphene/Si diode are performed to analyze the electronic band structure of the TiO2/graphene/Si system, based on which we finally present the enhancement mechanism of photodetection using TiO2 NPs.

We report the design and preparation of graphene and polyaniline (PANI) woven-fabric composite films by in situ electropolymerization. The introduction of PANI greatly improves the electrochemical properties of solid-state supercapacitors which possess capacitances as high as 23 mF cm(-2), and exhibit excellent cycling stability with ∼ 100% capacitance retention after 2000 cycles. The devices have displayed superior flexibility with improved areal specific capacitances to 118% during deformation.

Carbon nanotube (CNT) films are promising materials for constructing highly flexible composites for supercapacitor electrodes. Here, we prepared composite films with a sandwich structure and outstanding electrochemical properties by electrodepositing manganese oxide (MnOx) on the flexible CNT macrofilms. All-solid-state supercapacitors were then fabricated from the CNT–MnOx composite films using poly(vinylalcohol)–potassium hydroxide as the gel electrolyte. The supercapacitors have a high performance with a specific capacitance of 73.4 F g−1 and an energy density of 6.2 W h kg−1. The supercapacitors also exhibit high flexibility and stability under bending and kneading. When cut into small parts, the supercapacitor fragments can still work independently. The highly flexible and tailorable supercapacitors have great potential in flexible electronics in the future.

With the combination of surfactant and freeze-drying, we have developed two kinds of graphene spongy structures. On the one hand, using foams of soap bubbles as templates, three-dimensional porous graphene sponges with rich hierarchical pores have been synthesized. Pores of the material contain three levels of length scales, including millimeter, micrometer and nanometer. The structure can be tuned by changing the freezing media, adjusting the stirring rate or adding functional additives. On the other hand, by direct freeze-drying of a graphene oxide/surfactant suspension, a porous framework with directionally aligned pores is prepared. The surfactant gives a better dispersion of graphene oxide sheets, resulting in a high specific surface area. Both of the obtained materials exhibit excellent absorption capacity and good compression performance, providing a broad range of possible applications, such as absorbents, storage media, and carriers.

Sensing strain of soft materials in small scale has attracted increasing attention. In this work, graphene woven fabrics (GWFs) are explored for highly sensitive sensing. A flexible and wearable strain sensor is assembled by adhering the GWFs on polymer and medical tape composite film. The sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication, ease to follow human skin deformation, and so on. Some weak human motions are chosen to test the notable resistance change, including hand clenching, phonation, expression change, blink, breath, and pulse. Because of the distinctive features of high sensitivity and reversible extensibility, the GWFs based piezoresistive sensors have wide potential applications in fields of the displays, robotics, fatigue detection, body monitoring, and so forth.

In the version of the article originally published in the volume 62, issue 7, 2019 of Sci China Mater (2019, 62 (7): 947–954, https://doi.org/10.1007/s40843-018-9399-3 ), the authors used a wrong figure (Fig. 1) by mistake. The corrected version of Fig. 1 appears below.

In nature, some animals change their deceptive coloration for camouflage, temperature preservation or communication. This astonishing function has inspired scientists to replicate the color changing abilities of animals with artificial skin. Recently, some studies have focused on the smart materials and devices with reversible color changing or light-emitting properties for instantaneous strain visualization. However, most of these works only show eye-detectable appearance change when subjected to large mechanical deformation (100%–500% strain), and conspicuous color change at small strain remains rarely explored. In the present study, we developed a user-interactive electronic skin with human-readable optical output by assembling a highly sensitive resistive strain sensor with a stretchable organic electrochromic device (ECD) together. We explored the substrate effect on the electromechanical behavior of graphene and designed a strategy of modulus-gradient structure to employ graphene as both the highly sensitive strain sensing element and the insensitive stretchable electrode of the ECD layer. Subtle strain (0–10%) was enough to evoke an obvious color change, and the RGB value of the color quantified the magnitude of the applied strain. Such high sensitivity to smaller strains (0–10%) with color changing capability will potentially enhance the function of wearable devices, robots and prosthetics in the future.

Reduced graphene oxide (RGO) has been employed as an electrode for a series of vertically structured photodetectors. Compared with mechanically exfoliated or chemical vapor deposited graphene, RGO possesses more oxygen containing groups and defects, which are proved to be favorable to enhance the performance of photodetectors. As a matter of fact, RGO with different reduction levels can be readily obtained by varying the annealing temperature. The synthesis procedures for the RGO material are suitable for large scale production and its performance can be effectively improved by functionalization or element doping. For RGO-based devices, the Schottky junction properties and photoelectric conversion have been investigated, primarily by analyzing their current–voltage characteristics. Subsequently, the ON/OFF ratio, responsivity and detectivity of the photodetectors were closely examined, proving that the RGO material could be effectively utilized as the electrode material; also, their relationship with the RGO reduction levels has also been explored. By analyzing the response/recovery speed of the RGO-based photodetectors, we have studied the effects of oxygen-containing functional groups and crystalline defects on the photoelectric conversion.

Reduced graphene oxide (RGO)/Si Schottky diode has been reported nowadays to show excellent performances in photodetection and other photoelectrical devices. Different from pure graphene, there are large amounts of function groups and structural defects left on the base plane of RGO, which may influence the interfacial properties of RGO/Si Schottky diode. Herein, the barrier inhomogeneity and junction characteristics were systematically investigated to help to describe the interface of RGO/Si diode. From the perspective of its applications, the influences of gas molecule and noiseproperties are considered to be important. Thus, the photovoltaic performance of RGO/Si devices in air and vacuum is investigated to analyze their effects. Meanwhile, 1/fnoise of RGO/Si diodes is investigated under air/vacuum conditions and varied temperatures. It is found that the devices in vacuum and under higher power incident light show much lower 1/fnoise. These results are meaningful to the noise control and performance improvement in the development of Schottky diode based devices.

Flow-induced voltage generation on graphene has attracted great attention, but harvesting voltage by ionic liquid continuously flowing along graphene at macro-scale is still a challenge. In this work, we design a network structure of graphene grids (GG) woven by crisscrossed graphene micron-ribbons. The structure is effective in splitting the continuous fluid into “droplets” to generate consistent voltage using the mechanism of electrochemical energy generation. Key parameters such as flow rate, mesh number of GG, and slope angle are optimized to obtain maximum voltage in energy generation. The results suggest great potential of this graphene-based generator for future applications in energy harvesting.

All carbon coaxial supercapacitors based on hollow carbon nanotube (CNT) sleeve structure are assembled and tested. The key advantage of the structure is that the inner core electrode is variable from CNT sleeve sponges, to CNT fibers, reduced graphene oxide fibers, and graphene woven fabrics. By changing core electrodes from sleeve sponges to CNT fibers, the electrochemical performance has been significantly enhanced. The capacitance based on sleeve sponge + CNT fiber double the capacitances of double-sleeve sponge supercapacitors thanks to reduction of the series and internal resistances. Besides, the coaxial sleeve structure possesses many other features, including high rate capacitance, long cycle life, and good flexibility.

A hybrid heterojunction and solid-state photoelectrochemical solar cell based on graphene woven fabrics (GWFs) and silicon is designed and fabricated. The GWFs are transferred onto n-Si to form a Schottky junction with an embedded polyvinyl alcohol based solid electrolyte. In the hybrid solar cell, solid electrolyte serves three purposes simutaneously; it is an anti-reflection layer, a chemical modification carrier, and a photoelectrochemical channel. The open-circuit voltage, short-circuit current density, and fill factor are all significantly improved, achieving an impressive power conversion efficiency of 11%. Solar cell models are constructed to confirm the hybrid working mechanism, with the heterojunction junction and photoelectrochemical effect functioning synergistically.

Very less attention has been paid recently to the electrochemical properties of graphene films with intrinsic flat structure prepared by chemical vapor deposition (CVD). In this work, button supercapacitors were fabricated using ionic liquid as electrolytes and layer-by-layer graphene structures as electrodes. The specific capacitances of the supercapacitors increased with the increase of layer number. The areal specific capacitance of ten-layer graphene supercapacitor was 0.29 mF/cm2 at the scan rate of 50 mV/s, which was about three times of that of monolayer graphene supercapacitor (0.1 mF/cm2). The sandwiched multi-layer structures with oxide deposition further improved the device performance. However, the polycrystalline nature of CVD-grown graphene films introduced structural instability during charge-discharge process, resulting in degraded capacitive performance and cycling stability. Our results suggest that graphene films with intrinsic “in-plane” structure might not be ideal candidates for electrode materials.