Chengyi Hou

Highly Conductive, Flexible, and Compressible All‐Graphene Passive Electronic Skin for Sensing Human Touch

A facile and passive multiply flexible thin-film sensor is demonstrated based on thermoelectric effects in graphene. The sensor is highly conductive, free-standing, flexible, and elastic. It senses heat and cold, and measures heated/cooled areas; it also discerns human touch from other pressures, locates human touch, and measures pressure levels. All of these sensing abilities are demonstrated without any internal/external power supply.

P25–graphene hydrogels: Room-temperature synthesis and application for removal of methylene blue from aqueous solution

Herein we report a room-temperature synthesis of chemically bonded TiO2 (P25)-graphene composite hydrogels and their use as high performance visible light photocatalysts. The three-dimensional (3D) TiO2-carbon composite exhibits a significant enhancement in the reaction rate in the decontamination of methylene blue, compared to the bare P25. The 3D P25-graphene hydrogel is much easier to prepare and apply as a macroscopic device, compared to the 2D P25-graphene sheets. This work could provide new insights into the room-temperature synthesis of graphene-based materials. As a kind of the novel 3D graphene-based composite, the obtained high performance P25-graphene gel could be widely used in the environmental protection issues.

Origami-inspired active graphene-based paper for programmable instant self-folding walking devices

Origami-inspired self-folding graphene papers show remote control grasping, manipulation, and walking behaviors. Origami-inspired active graphene-based paper with programmed gradients in vertical and lateral directions is developed to address many of the limitations of polymer active materials including slow response and violent operation methods. Specifically, we used function-designed graphene oxide as nanoscale building blocks to fabricate an all-graphene self-folding paper that has a single-component gradient structure. A functional device composed of this graphene paper can (i) adopt predesigned shapes, (ii) walk, and (iii) turn a corner. These processes can be remote-controlled by gentle light or heating. We believe that this self-folding material holds potential for a wide range of applications such as sensing, artificial muscles, and robotics.

Bio-applicable and electroactive near-infrared laser-triggered self-healing hydrogels based on graphene networks

For biomimetic applications, an artificial material is needed to be self-healing, electroactive and bio-applicable. Herein we report a strategy to build a graphene–poly(N,N-dimethylacrylamide) (PDMAA) cross-linking structure based on graphene networks. The obtained hydrogel exhibits good neural compatibility, high conductivity, low impedance and efficient near-infrared-triggered photothermal self-healing behaviour owing to its unique 3-dimensional graphene–PDMAA cross-linking networks. The results indicate that the graphene–PDMAA hydrogel has potential for application as an artificial tissue.

An Elastic Transparent Conductor Based on Hierarchically Wrinkled Reduced Graphene Oxide for Artificial Muscles and Sensors

Using a 3D stretching method, a highly elastic reduced graphene oxide (rGO)/polyacrylic ester hierarchically wrinkled elastic transparent conductor (HWETC) is fabricated. Periodic hierarchical N-rGO layer wrinkling allows the HWETC to show high conductivity (100-457 Ω ◻-1 ) and transmittance (67-85%) under substantial stretching (>400%) and bending deformation (≈180°), which enables electrothermal actuation and strain sensing.

Functionalization of PNIPAAm microgels using magnetic graphene and their application in microreactors as switch materials

Aqueous-dispersed graphene/Fe3O4 hybrids are prepared using a two-step method. Functional microgels composed of the poly(N-isopropylacrylamide) (PNIPAAm) and the as-prepared graphene/Fe3O4 hybrids are synthesized in a microfluidic reactor for the first time. The microgel exhibits a good response to an external magnet and near-infrared (NIR) laser irradiation, indicating that it could be used as a light-driven and magnetic controlled switch for applications in microreactors.

Rapid formation of superelastic 3D reduced graphene oxide networks with simultaneous removal of HI utilizing NIR irradiation

Graphene foam with three-dimensional (3D) networks was formed following removal of the undesirable toxic iodide induced in a HI reduced GO film through NIR light irradiation via a near infrared (NIR) light irradiation method under ambient laboratory conditions. Compact reduced graphene oxide films were used as the precursors which were fabricated through vacuum filtration and HI reduction. A series of graphene foams which have alterable pore sizes ranging from a few to hundred micrometers rapidly formed under NIR light irradiation at different power densities. The graphene foam has an ultimate tensile strength of about 15.3 MPa and could be compressed at a very large strain (e = 60%) for 200 cycles without significant plastic deformation or degradation in compressive strength. This 3D graphene network is hydrophobic and showed high absorbing abilities for organic liquids. The adsorbed oil weight is up to about 27 times the weight of graphene foam after being immersed in an oil–water mixture for two minutes, and 87.2% of adsorbed oil could be squeezed out and recycled. This process is highly repeatable, which makes our product a potential candidate for removal and recycling of oil for environmental protection.

Ultrathin, Washable, and Large-Area Graphene Papers for Personal Thermal Management

Freestanding, flexible/foldable, and wearable bifuctional ultrathin graphene paper for heating and cooling is fabricated as an active material in personal thermal management (PTM). The promising electrical conductivity grants the superior Joule heating for extra warmth of 42 °C using a low supply voltage around 3.2 V. Besides, based on its high out-of-plane thermal conductivity, the graphene paper provides passive cooling via thermal transmission from the human body to the environment within 7 s. The cooling effect of graphene paper is superior compared with that of the normal cotton fiber, and this advantage will become more prominent with the increased thickness difference. The present bifunctional graphene paper possesses high durability against bending cycles over 500 times and wash time over 1500 min, suggesting its great potential in wearable PTM.

Reduced graphene oxide functionalized stretchable and multicolor electrothermal chromatic fibers

A stretchable and multicolor electrothermal chromatic fiber is prepared based on reduced graphene oxide (RGO) functionalized elastic conductive fibers and various thermochromic materials. The colors of the fibers can be switched within 15s due to the good resistive-heating performance of the conductive fibers. Through a combination of different thermochromic materials, abundant and reversible color changes are clearly observed by the naked eye (e.g., from orange, red, green to yellow, purple, blue and white, respectively). Moreover, the fibers exhibit excellent color changing stability even after 1000 resistive-heating or stretching/releasing cycles owing to the structural stability of the multilayered fibers and the excellent electrothermal stability of RGO. Finally, they are easily woven into textiles and plaited into colorful hand chains, which showed huge application value especially for stretchable visual sensors and clothing integrated wearable displays.

Prepolymerization-assisted fabrication of an ultrathin immobilized layer to realize a semi-embedded wrinkled AgNW network for a smart electrothermal chromatic display and actuator

Silver nanowire/poly(dimethylsiloxane) (AgNW/PDMS)-based stretchable conductive films are widely studied due to their excellent comprehensive performances mainly derived from the great electrical conductivity of AgNWs together with the excellent mechanical and optical properties of PDMS. However, their further applications have been limited by two fatal shortcomings: the low surface energy of PDMS and poor elongation at break of AgNWs. Herein, an ultrathin PDMS-immobilized layer was prepared to construct a semi-embedded wrinkled AgNW network and overcome the limitations through spin-coating the pre-polymerized PDMS solution. As a result, the as-prepared transparent stretchable AgNW/PDMS composite films with different AgNW loadings demonstrate great transmittance, conductivity, tensile stability under 40% and 60% strains, and adhesion of AgNWs on the PDMS substrate. With a further increase of AgNW loadings, reflective stretchable conductive films were obtained and they showed a much lower sheet resistance (∼0.2 Ω sq−1) and good tensile stability under 70% strain. Based on these stretchable conductive films, stretchable electrothermal chromatic films and electrothermal actuators were fabricated to demonstrate their multifunctional applications.