We have investigated thermal conductivity of graphene laminate films deposited on polyethylene terephthalate substrates. Two types of graphene laminate were studied, as deposited and compressed, in order to determine the physical parameters affecting the heat conduction the most. The measurements were performed using the optothermal Raman technique and a set of suspended samples with the graphene laminate thickness from 9 to 44 μm. The thermal conductivity of graphene laminate was found to be in the range from 40 to 90 W/mK at room temperature. It was found unexpectedly that the average size and the alignment of graphene flakes are more important parameters defining the heat conduction than the mass density of the graphene laminate. The thermal conductivity scales up linearly with the average graphene flake size in both uncompressed and compressed laminates. The compressed laminates have higher thermal conductivity for the same average flake size owing to better flake alignment. Coating plastic materials with thin graphene laminate films that have up to 600× higher thermal conductivity than plastics may have important practical implications.

In this paper, we demonstrate realization of printable radio frequency identification (RFID) antenna by low temperature processing of graphene ink. The required ultra-low resistance is achieved by rolling compression of binder-free graphene laminate. With compression, the conductivity of graphene laminate is increased by more than 50 times compared to that of as-deposited one. Graphene laminate with conductivity of 4.3 × 104 S/m and sheet resistance of 3.8 Ω/sq (with thickness of 6 μm) is presented. Moreover, the formation of graphene laminate from graphene ink reported here is simple and can be carried out in low temperature (100 °C), significantly reducing the fabrication costs. A dipole antenna based on the highly conductive graphene laminate is further patterned and printed on a normal paper to investigate its RF properties. The performance of the graphene laminate antenna is experimentally measured. The measurement results reveal that graphene laminate antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns, making it ideal for low cost printed RF applications, such as RFID tags and wearable wireless sensor networks.

Supercapacitors (also called electrochemical capacitors or ultracapacitors) offering transient but ultrahigh power for the time-dependent needs of electrical vehicles, solar and wind power, digital telecommunication systems, and fuel cells have attracted substantial attention because of their unique merits, such as high power density, long cycle life, and low environmental impact. [ 1 ] Many electrochemically active materials, including ruthenium oxide (RuO 2 ), [ 2 ] cobalt oxide (CoO x ), [ 3 ] nickel oxide (NiO x ), [ 4 ] iridium oxide (IrO 2 ), [ 5 ] vanadium oxides (V 2 O 5 , VO x ), [ 6 ] manganese oxides (MnO 2 , Mn 3 O 4 ), [ 7 ] and conducting polymers [ 8 ] have been introduced and applied as electrode materials for supercapacitors of the redox type. Among these electroactive materials, ruthenium oxide is superior to others owing to its high electrochemical reversibility, high-power characteristics, excellent stability, and improved frequency responses. [ 9 ] However, the rarity of ruthenium oxide limits the commercialization of supercapacitors based on this material.Combining ruthenium oxide with other materials is a solution to this problem and has been widely investigated. For example, Ru-based oxides such as (Ru-Ir)O 2 , [ 10 ] (Ru-Sn)O 2 , [ 11 ] and (Ru-Ti)O 2 [ 12 ] have been synthesized using controlled sol-gel methods. In addition, various carbon materials, such as activated carbon, [ 13 ] CNTs, [ 14 ] mesoporous carbon, [ 15 ] and graphene, [ 16 ] have been used as hosts for loading ruthenium oxide (SI , Table S1). Although these techniques can reduce the amount of ruthenium oxide required for supercapacitors, desired proton conductivity in Ru-based materials is diffi cult to achieve. Because the superfi cial redox transitions of RuO 2 involve the proton and electron double injecting/expelling process, [ 9 , 17 ] RuO 2 crystals with the hydrous nature in the electrolyte-electrode interface region generally show an ideal electrochemical reversibility for supercapacitors. Hence, establishing a crystalline but hydrous RuO 2 layer on the external surfaces of a three-dimensionally (3D) mesoporous silica nanoparticles (MSNs) has advantages over the conventional carbon-based hosts because of the high surface area, uniform pore size and hydrophilic surface property. These advantages of MSNs can simultaneously increase electrochemically active centers, promote electrolyte penetration, and enhance electron transport, which fulfi lls the requirements of the next-generation supercapacitors. Sugimoto et al. have demonstrated a new ruthenium oxide-based material, the ruthenic acid nanosheet, which uses its interlayer surface for both pseudo and double-layer capacitance. [ 18 ] Moreover, utilization of electrochemically active materials and power capabilities are closely related to the specifi c surface area and pore size distribution of electrode materials. [ 9 , 19 ] Consequently, constructing mesoporous structures for electrode materials with high specifi c surface areas and abundant mesopores, such a...

No abstract

No abstract