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 ...
