Xiaobei Zang

Highly Flexible and Adaptable, All‐Solid‐State Supercapacitors Based on Graphene Woven‐Fabric Film Electrodes

Recently, the applications of portable and fl exible devices have come to fruition, for instance, devices like fl exible touch screens [ 1 ] and fl exible solar cells [ 2 ] have become daily essentials. Such breakthroughs have dramatically stimulated the development of related technologies, such as the design and construction of energy-storage devices, one of the most important devices for human prosperity and health. Supercapacitors, which are also called electrochemical capacitors, are fast but high-power energy-storage devices. [ 3–5 ] In such devices, charges are stored in the interface of electrolyte and electrode material through the rapid and reversible adsorption/desorption of ions. [ 6,7 ] Much effort has also been made to develop thin-fi lm supercapacitors, [ 8,9 ] which are expected to possess high capacity while maintaining light weight and fl exibility. Theoretically, the two-dimensional (2D) extension of thin-fi lm supercapacitors could substantially reduce the deformation resistance from the vertical direction, which ultimately would make the entire device thin, fl exible, and easy to fold, twist, or reshape. The travel distance of electrolyte ions in thin-fi lm supercapacitors is also shorter than their counterparts. [ 10 ] Consequently, all-solid-state supercapacitors,

Ultra-sensitive graphene strain sensor for sound signal acquisition and recognition

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.

Effect of different gel electrolytes on graphene-based solid-state supercapacitors

A solid-state supercapacitor with a flexible, simple structure based on graphene thin film electrodes and acid/base/salt–PVA gel electrolytes is reported. The performance of six different gel electrolytes (H3PO4, H2SO4, KOH, NaOH, KCl, NaCl) in this graphene-based supercapacitor are investigated. The electrochemical properties of this highly flexible, stable supercapacitor are enhanced by optimizing the concentration of the electrolyte in polymer gel.

Three-dimensional porous graphene sponges assembled with the combination of surfactant and freeze-drying

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.

Photo-Promoted Platinum Nanoparticles Decorated MoS2@Graphene Woven Fabric Catalyst for Efficient Hydrogen Generation

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.

TiO2 enhanced ultraviolet detection based on a graphene/Si Schottky diode

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.

Evaluation of layer-by-layer graphene structures as supercapacitor electrode materials

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.

All carbon coaxial supercapacitors based on hollow carbon nanotube sleeve structure

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.

Galvanism of continuous ionic liquid flow over graphene grids

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.

Schottky diode characteristics and 1/f noise of high sensitivity reduced graphene oxide/Si heterojunction photodetector

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.