Rujing Zhang

Stretchable and highly sensitive graphene-on-polymer strain sensors

The use of nanomaterials for strain sensors has attracted attention due to their unique electromechanical properties. However, nanomaterials have yet to overcome many technological obstacles and thus are not yet the preferred material for strain sensors. In this work, we investigated graphene woven fabrics (GWFs) for strain sensing. Different than graphene films, GWFs undergo significant changes in their polycrystalline structures along with high-density crack formation and propagation mechanically deformed. The electrical resistance of GWFs increases exponentially with tensile strain with gauge factors of ~103 under 2~6% strains and ~106 under higher strains that are the highest thus far reported, due to its woven mesh configuration and fracture behavior, making it an ideal structure for sensing tensile deformation by changes in strain. The main mechanism is investigated, resulting in a theoretical model that predicts very well the observed behavior.

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.

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.

Proposed model for calculating the standard formation enthalpy of binary transition-metal systems

In this letter, we present a proposed model for calculating the standard formation enthalpy of binary transition-metal systems by adding a prefactor S(c) to the well-documented formula developed by Miedema. The main idea is to take into account the significant effect of the atomic size difference on the contact surface while two dissimilar metals approaching together. Employing this model, the standard formation enthalpies of some 260 intermetallic compounds were calculated and compared with the experimentally measured data. It was found that the precision of the calculated values by the proposed model could be improved 13%–65% and that statistically, over 95% of the calculated values were in agreement with the experimental ones within an error of ±23 kJ/mol, while employing the Miedema’s formula the agreement was about 80%.

Flexible graphene woven fabrics for touch sensing

Graphene woven fabric (GWF) prepared from chemical vapor deposition was used as smart self-sensing element to assemble piezoresistor through directly transferring onto the flexible substrate poly(dimethylsiloxane) (PDMS) with the deposited Ti/Au electrodes. A rational strategy was proposed to fabricate flexible touch sensors easily and effectively with the full usage of the mechanical and electrical properties of GWF, whose resistance is highly sensitive to macro-deformation or micro-defect. Compared to commercial and traditional touch sensing, the GWF-on-PDMS piezoresistor is structurally flexible that is demanded under special conditions and meanwhile makes the piezoresistor to have excellent durability.

Cellulose-Templated Graphene Monoliths with Anisotropic Mechanical, Thermal, and Electrical Properties.

Assembling particular building blocks into composites with diverse targeted structures has attracted considerable interest for understanding its new properties and expanding the potential applications. Anisotropic organization is considered as a frequently used targeted architecture and possesses many peculiar properties because of its unusual shapes. Here, we show that anisotropic graphene monoliths (AGMs), three-dimensional architectures of well-aligned graphene sheets obtained by a dip-coating method using cellulose acetate fibers as templates show thermal-insulating, fire-retardant, and anisotropic properties. They exhibit a feature of higher mechanical strength and thermal/electrical conductivities in the axial direction than in the radial direction. Elastic polymer resins are then introduced into the pores of the AGMs to form conductive and flexible composites. The composites, as AGMs, retain the unique anisotropic properties, revealing opposite resistance change under compressions in different directions. The outstanding anisotropic properties of AGMs make them possible to be applied in the fields of thermal insulation, integrated circuits, and electromechanical devices.

A Flexible Platform Containing Graphene Mesoporous Structure and Carbon Nanotube for Hydrogen Evolution

It is of great significance to design a platform with large surface area and high electrical conductivity for poorly conductive catalyst for hydrogen evolution reaction (HER), such as molybdenum sulfide (MoSx), a promising and cost‐effective nonprecious material. Here, the design and preparation of a free‐standing and tunable graphene mesoporous structure/single‐walled carbon nanotube (GMS/SWCNT) hybrid membrane is reported. Amorphous MoSx is electrodeposited on this platform through a wet chemical process under mild temperature. For MoSx@GMS/SWCNT hybrid electrode with a low catalyst loading of 32 μg cm−2, the onset potential is near 113 mV versus reversible hydrogen electrode (RHE) and a high current density of ≈71 mA cm−2 is achieved at 250 mV versus RHE. The excellent HER performance can be attributed to the large surface area for MoSx deposition, as well as the efficient electron transport and abundant active sites on the amorphous MoSx surface. This novel catalyst is found to outperform most previously reported MoSx‐based HER catalysts. Moreover, the flexibility of the electrode facilitates its stable catalytic performance even in extremely distorted states.

Sponge-like nickel phosphide–carbon nanotube hybrid electrodes for efficient hydrogen evolution over a wide pH range

Cost-effective hydrogen production via electrolysis of water requires efficient and durable earth-abundant catalysts for the hydrogen evolution reaction (HER) over a wide pH range. Herein, we report sponge-like nickel phosphide–carbon nanotube (NixP/CNT) hybrid electrodes that were prepared by facile cyclic voltammetric deposition of amorphous NixP catalysts onto the threedimensional (3D) porous CNT support. These compounds exhibit superior catalytic activity for sustained hydrogen evolution in acidic, neutral, and basic media. In particular, the NixP/CNT electrodes generate cathodic currents of 10 and 100 mA·cm−2 at overpotentials of 105 and 226 mV, respectively, in a 1 M phosphate buffer solution (pH = 6.5) with a Tafel slope of 100 mV·dec−1; the currents were stable for over 110 h without obvious decay. Our results suggest that the 3D porous CNT electrode supports could serve as a general platform for earth-abundant HER catalysts for the development of highly efficient electrodes for hydrogen production.

Graphene oxide-embedded polyamide nanofiltration membranes for selective ion separation

Herein, a graphene oxide (GO)-modified piperazine (PIP) nanofiltration (NF) membrane was successfully fabricated via in situ interfacial polymerization of PIP-GO and trimesoyl chloride on a porous substrate, in which GO induced a wrinkled membrane surface with improved roughness and hydrophilicity and reduced electronegativity. Ion separation tests show that GO increases the water flux of the membranes significantly by 10–15 LMH for all the studied salt solutions. Furthermore, GO can selectively increase the retention of CaCl2 and MgCl2, but slightly decrease the rejection of MgSO4, NaCl, and KCl; this indicates an improvement in the separation performance of the PIP-GO membrane between divalent and monovalent cations with a common counter ion, Cl−. The enhanced water permeation of the PIP-GO membrane can be ascribed to its increased surface area, hydrophilicity, and ultrafast water transport between GO nanosheets. The GO-promoted selective ion separation is the result of an attenuated electrostatic attraction between Ca2+, Mg2+, and the membrane as well as the water flow-accelerated transport of Na+ and K+. Therefore, GO-modified NF membranes exhibit great potential for applications in the areas of water purification and separation.

Rapid Liquid Recognition and Quality Inspection with Graphene Test Papers

Electronic tongue is widely applied in liquid sensing for applications in various fields, such as environmental monitoring, healthcare, and food quality test. A rapid and simple liquid‐sensing method can greatly facilitate the routine quality tests of liquids. Nanomaterials can help miniaturize sensing devices. In this work, a broad‐spectrum liquid‐sensing system is developed for rapid liquid recognition based on disposable graphene–polymer nanocomposite test paper prepared through ion‐assisted filtration. Using this liquid‐sensing system, a number of complex liquids are successfully recognized, including metal salt solutions and polymer solutions. The electronic tongue system is especially suitable for checking the quality of the foodstuff, including soft drinks, alcoholic liquor, and milk. The toxicants in these liquids can be readily detected. Furthermore, the novel material‐structure design and liquid‐detection method can be expanded to other chemical sensors, which can greatly enrich the chemical information collected from the electrical response of single chemiresistor platform.