wileyonlinelibrary.comactuators, [ 6 ] and absorbers of environmental pollution. [ 2,7 ] Among graphenebased materials, graphene oxides (GOs) can be described as "up-and-coming" material candidates because they are thin, light, strong, environmentally friendly, and fl exible. They also have high surface area, excellent mechanical-chemical properties, and the ability to conduct electricity within 2D nanostructures. Many research groups [ 8 ] have reported the simple preparation of rGO aerogels from GO solution by hydrothermal and freeze-drying methods or etching methods, employing a spherical template/GO composite. The microstructural features of rGO aerogels make them some of the most promising building blocks for energy-related and environmental applications. This is because these features can greatly improve working-volume deformability, can form a multidimensional conduction network, and can provide 3D interfacing or intercalation with other system components (e.g., electrolytes, reactants). [ 8 ] However, the performance and diversity of such graphene aerogel conductors are limited by the lack of a suffi cient compressive modulus (that is, they are fragile and collapse under stress). [ 4,9 ] Aerogels usually have an extremely low density due to their relatively high rigidity and/or a rather low electrical conductivity (e.g., 0.12 S m −1 with a density of 5.10 mg cm −3 ). [ 10 ] These properties can result from an incomplete reduction if mild chemical reducing conditions are employed without thermal annealing. Zhao et al. [ 11 ] reported the development of a compression-tolerant rGO sponge supercapacitor with a polypyrrole coating, which is conductive and provides mechanical reinforcement. This work showed that the use of rGO sponges in conjunction with other materials can overcome some of the shortcomings of monolithic rGO sponges. Recently, Wu et al. [ 12 ] fabricated a spongy graphene material (density = 1.15 mg cm −3 ; conductivity = 0.37 S m −1 ) that showed compressive elasticity and a near-zero Poisson's ratio by using a solvo-thermal reaction and thermal annealing. The primary remaining challenge is the synthesis of additive-free monolithic rGO aerogels that preserve the low density, high conductivity, and good elasticity inherent in GO nanosheets.In this article, we describe the development of a facile approach for fabricating support-free monolithic nitrogen (N)-doped rGO aerogels using a simple hydrothermal method employing hexamethylenetetramine (HMTA) as a stabilizerThe simple synthesis of ultralow-density (≈2.32 mg cm −3 ) 3D reduced graphene oxide (rGO) aerogels that exhibit high electrical conductivity and excellent compressibility are described herein. Aerogels are synthesized using a combined hydrothermal and thermal annealing method in which hexamethylenetetramine is employed as a reducer, nitrogen source, and graphene dispersion stabilizer. The N-binding confi gurations of rGO aerogels increase dramatically, as evidenced by the change in pyridinic-N/quaternary-N ratio. The conductivity ...

Lightweight, simple and flexible self-powered photodetectors are urgently required for the development and application of advanced optical systems for the future of wearable electronic technology. Here, using a low-temperature reduction process, we report a chemical approach for producing freestanding monolithic reduced graphene oxide papers with different gradients of the carbon/oxygen concentration ratio. We also demonstrate a novel type of freestanding monolithic reduced graphene oxide self-powered photodetector based on a symmetrical metal–semiconductor–metal structure. Upon illumination by a 633-nm continuous wave laser, the lateral photovoltage is observed to vary linfearly with the laser position between two electrodes on the reduced graphene oxide surface. This result may suggest that the lateral photovoltaic effect in the reduced graphene oxide film originates from the built-in electric field by the combination of both the photothermal electric effect and the gradient of the oxygen-to-carbon composition. These results represent substantial progress toward novel, chemically synthesized graphene-based photosensors and suggest one-step integration of graphene-based optoelectronics in the future.

of both electrolyte penetration and electron transportation for next-generation power devices. Currently, the most commonly used 3D porous metal foam in electrodes is nickel as a current collector, which has a high conductivity (≈350 S cm −1 ). [4] However, this metal foam is not appropriate for flexible supercapacitors and electronics because they cannot return to their initial shape after even slight strains such as uniaxial compression, bending, and twisting. To resolve the challenges of flexibility, the unique functionalization of commercial sponges (e.g., polyurethane or melamine sponges) with 3D open-cell structure analogue metal foams as a template has attracted intensive research interest for solving energy and environmental issues because of the low cost, ease of fabrication, 3D porous structures, light weight, and high flexibility. Thus, plastic sponges have drawn significant attention as a support and/or template to construct 3D active materials. However, these polymer foams are electrical insulators. Consequently, tremendous efforts have been devoted to synthesize 3D network conductors on commercial sponges by simply dipcoating (reduced) graphene oxides and/or carbon-nanotube dispersion and/or pyrolized carbon sponges. [5][6][7][8][9][10][11][12][13][14] However, it is difficult to produce carbonaceous foams/sponges in a large scale because of their relatively high-cost and harsh processing conditions (high-temperature carbonization: ≈800-1000 °C)]. [15] Furthermore, because of the high resistance of carbon-based materials, for example, 0.34 S cm −1 carbonized polyurethane foam (0.34 S cm −1 ), [16] reduced graphene oxide coated on polyurethane foam (0.0009-0.0025 S cm −1 ), [17] and carbon nanotube coated on polyurethane (1 S cm −1 ), [18] these supercapacitor sponges face issues in high internal resistance. [19,20] Their performance in terms of electrical conductivity remains inferior to that of metal foams, which results in a reduced power density. Lately, the ramifications of 3D networks with high conductivity as substrate templates have been a notably fascinating topic for energy and/or sensing from both scientific and technological viewpoints. [7,8,[21][22][23][24][25][26][27][28][29][30] Therefore, there is an urgent need for a new class of flexible 3D open-porous substrates to develop advanced energy-related storages with enhanced energy density without sacrificing the power delivery and cycle stability to satisfy the future flexible energy-related demands. Nonetheless, Although increasing attention has been paid to wearable electronic devices in recent years, flexible supercapacitors with high performance remain not readily available because of the limitations of flexible electrode types. A highly conductive 3D macroporous sponge is fabricated by coating poly(3,4-ethyl enedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/silver nanowires (AgNWs) on a commercial sponge using a simple and low-cost "immersion method." The fabricated flexible 3D sponge conductor shows a high electrical conductiv...

To achieve high energy storage on three-dimensional (3D) structures at low cost, materials with high power and long cycle life characteristics have to be developed. We synthesized ZnCo O /reduced graphene oxide (rGO) binary composites in commercial sponges. ZnCo O nanosheets were grown on the surface of GO/sponge through a hydrothermal reaction. The resulting flexible, free-standing ZnCo O /rGO/sponge electrodes were used as the electrodes in a symmetric supercapacitor. ZnCo O /rGO/sponge electrodes have a large specific capacitance of 1116.6 F g at a scan rate of 2 mV s in aqueous electrolyte. The all-solid-state flexible supercapacitor is assembled based on ZnCo O /rGO/sponge electrodes, which show excellent electrochemical performances with a specific capacitance of 143 F g at a current density of 1 A g . The as-fabricated supercapacitor also exhibits excellent cycling stability (93.4 % capacitance retention after 5000 cycles) and exceptional mechanical flexibility. These results demonstrate the potential of ZnCo O /rGO/sponge as an electrode in flexible, high-performance supercapacitors.

Microstructural changes in Si/Ti/Al/Cu (10/40/60/50 nm) Ohmic contacts to AlGaN/GaN heterostructure were investigated for complementary metal-oxide semiconductor compatible processes. Si/Ti/Al/Cu metallization exhibited a low specific contact resistance of 3.6×10 −6 Ω-cm 2 and contact resistance of 0.46 Ω-mm when a Si interfacial layer was used. Without a designated barrier metal, TiSi x alloys that formed in the metallic region effectively suppressed Cu diffusion. The shallow TiN junction in AlGaN/GaN was attributed to TiSi x in the metallic regions. Microstructural changes were detected by systematic physical characterization.