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A thermally reduced graphene oxide film (r-GOF), with tailorable micro-structures and macro-properties, is fabricated by annealing a filtrated graphene oxide film (GOF) in a confined space. The structural evolution of the film at different annealing temperatures is systematically investigated, and further correlated to the thermal conductivity and mechanical performances. With the increase of temperature, more oxygencontaining functional groups are removed from the film by a simultaneous conversion from sp 3 to sp 2 carbon in the graphitic lattice. As the temperature reached 1200 C, the r-GOF achieves an ultrahigh thermal conductivity of ca. 1043.5 W m À1 K À1 , while 1000 C is a critical temperature in enhancing the thermal conductivity. Moreover, G1200 exhibits excellent mechanical stiffness and flexibility with a high tensile strength (13.62 MPa) and Young's modulus (2.31 GPa). The combined conductivity and mechanical performances render the r-GOFs promising materials as flexible lateral heat spreaders for electronics.

A high-rate graphene-based supercapacitor is very attractive for the practical application of graphene. Here, we first synthesized the films of the hybrids of biomass cellulose and large literal sheet sizes and weakly defective graphene flakes reaching high thermal conductivity and then converted them into hierarchical porous graphene carbon materials reaching superior supercapacity. The interconnected porous carbon framework, with macroporous walls sandwiched by micro/mesoporous activated carbon covering graphene flakes, was synthesized by template-free low-temperature activation of the cellulose/graphene hybrids at 650°C. The graphene flakes could probably assist both the decrease in the temperature of the chemical activation of cellulose and the formation of the hierarchical carbon pores without destroying their sp 2 bonds. The porous graphene carbon-based supercapacitors exhibit a reversible specific capacitance of ∼300 F/g and ultrahigh energy storage performance of 67 Wh/kg, 54 Wh/L, and 60 kW/kg over a 45 s discharge time. ■ INTRODUCTIONHigh-energy density storage and fast response supercapacitors are needed to serve the people to keep up with the high pace of modern life. 1−6 A hierarchical porous carbon framework with micro-, meso-, and macropores can be made into desirable electrodes for high-performance supercapacitors. 7−10 The macropores can work as a fast buffering reservoir for electrolytes, minimizing the diffusion distance of the ions and electrolytes from each pore, while the meso-and micropores provide a large accessible surface area for ion transport and charge accommodation. 11,12 Recently, porous graphene-based composites have received intense attention because the flat open atomic structure of graphene allows ions and electrolytes fast access to its surface with the result being a fast charging or discharging rate for energy storage. 13−17 On the other hand, although the theoretical specific surface area of a single graphene sheet is 2630 m 2 /g, experimentally accessible surface areas of graphene materials are far below this value because of the strong self-aggregation/stacking tendency of graphene flakes (GFs). To prevent the aggregation, many scientists and engineers are trying to design a three-dimensional (3D) framework, including converting flat flexible two-dimensional (2D) into 3D structure or making activated carbon and graphene hybrids. 18−22 Recently, Zhu and his co-workers 23 reported that reduced graphene oxide activated KOH at 800°C to yield a special 3D activated carbon analogue with a large surface area of >3000 m 2 /g as the electrode in a two-electrode symmetrical supercapacitor with excellent electrochemical performance. More recently, graphene oxide and polymer were also activated to produce 3D porous carbon with a large surface area and high specific capacity. 24,25 However, in most cases, (reduced) graphene oxides were used as a starting material, which remains costly and is not competitive with commercial activated carbon. In addition, (reduced) graphene oxides were c...