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Although lightweight and three-dimensional graphene aerogels and foams combining ultrahigh electrical conductivity, superelasticity and fatigue resistance are highly desirable for widespread applications, it remains a large challenge to construct a multifunctional framework affording the rapid electron transport and efficient load transfer due to the weak interfaces between highly reduced graphene oxide sheets. Herein, we report an efficient approach for fabricating an integrated graphene aerogel by bridging its reduced graphene oxide sheets with polyimide macromolecules followed by graphitization at 2800 °C. During the graphitization process, the reduced graphene oxide sheets are thermally reduced to graphene efficiently by removing their residual oxygen-containing groups and healing their defects, while the polyimide component is graphitized to turbostratic carbon to bridge the graphene sheets, resulting in an integrated graphene aerogel with satisfactory mechanical and functional performances, including ultrahigh electrical conductivity (>1000 S m−1) at a low density, unprecedented high electromagnetic interference shielding effectiveness of ∼83 dB in X-band, 90% reversible compressibility, and reliable resistance to fatigue for 1000 compressive cycles at 50% strain. The integrated graphene aerogels with such multifunctional performances hold a great promise for applications as electromagnetic interference shielding materials, oil adsorbents, and conductive scaffolds for polymer nanocomposites.

Highly efficient and lightweight electromagnetic interference (EMI) shielding materials have gained tremendous interests due to the urgent requirement for smart electronic devices and aerospace applications. Herein, we demonstrate a highly efficient hydrazine-induced foaming approach to fabricate magnetic, highly electrically conductive, and lightweight graphene/iron pentacarbonyl (IP) porous films for broadband EMI shielding application. The chitosan introduced effectively optimizes the microcellular structures by improving the interfacial adhesion between graphene sheets and thus enhances the electrical conduction of the porous films with IP flakes. The resultant porous structure not only reduces the density of the films, but also improves the electromagnetic radiation attenuation by repeated scattering of the incident microwave. The presence of magnetic IP flakes endows the porous film with magnetic property and enhanced EMI shielding performance by combining the dielectric and magnetic losses. Thus, the porous film with a small thickness of 0.3 mm and a low density of 0.12 g/cm 3 exhibits an excellent broadband EMI shielding performance of >38 dB in the frequency range of 8.2–59.6 GHz with a total bandwidth of 51.4 GHz. These results indicate that the lightweight porous film with outstanding magnetic and electrical properties could be used as multifunctional high-performance EMI shielding materials.

The increasingly severe electromagnetic pollution calls for high-performance microwave absorption materials. Lightweight, robust and porous MXene/polyimide (MP) aerogels with reversible compressibility, anisotropic pressure sensitivity and microwave absorption performances are fabricated by interface-reinforcement and bidirectional-freezing approach. The interfaces between MXene sheets are effectively reinforced by incorporated polyimide while anisotropic wave-like lamellar architectures are constructed during the bidirectional-freezing process due to the generated dual temperature-gradients. The highly anisotropic aerogel exhibits obvious higher mechanical strength and electrical conductivity along the lamella direction, but better elasticity and less energy dissipation in the normal direction. The reversibly compressible porous MP architecture not only delivers steady and repeatable electrical resistance response, but also presents long-term discernible direction-dependent pressure sensitivity for 1000 loading-release cycles at a strain of 50%. The anisotropic and porous architecture benefits microwave absorption. The structure optimization yields tunable effective absorption bandwidth (EAB) in a range of 3.9–18 GHz. Particularly, the MP aerogel shows the best EAB of 6.5 GHz for reported MXene-based microwave absorbers at only 1.91 mm, and the EAB covers the whole X-band for an aerogel with a thickness of 2.57 mm. These promising characteristics make the interfacially reinforced anisotropic MXene aerogels applicable for wearable piezoresistive devices and microwave absorbing materials.

2D transition metal carbides and nitrides (MXenes) have gained extensive attention recently due to their versatile surface chemistry, layered structure, and intriguing properties. The assembly of MXene sheets into macroscopic architectures is an important approach to harness their extraordinary properties. However, it is difficult to construct a freestanding, mechanically flexible, and 3D framework of MXene sheets owing to their weak intersheet interactions. Herein, an interfacial enhancement strategy to construct multifunctional, superelastic, and lightweight 3D MXene architectures by bridging individual MXene sheets with polyimide macromolecules is developed. The resulting lightweight aerogel exhibits superelasticity with large reversible compressibility, excellent fatigue resistance (1000 cycles at 50% strain), 20% reversible stretchability, and high electrical conductivity of ≈4.0 S m-1 . The outstanding mechanical flexibility and electrical conductivity make the aerogel promising for damping, microwave absorption coating, and flexible strain sensor. More interestingly, an exceptional microwave absorption performance with a maximum reflection loss of -45.4 dB at 9.59 GHz and a wide effective absorption bandwidth of 5.1 GHz are achieved.

Ultrathin, lightweight, and flexible electromagnetic-interference (EMI) shielding materials are urgently required to manage increasingly serious radiation pollution. 2D transition-metal carbides (MXenes) are considered promising alternatives to graphene for providing excellent EMI-shielding performance due to their outstanding metallic electrical conductivity. However, the hydrophilicity of MXene films may affect their stability and reliability when applied in moist or wet environments. Herein, for the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine-induced foaming process. In striking contrast to well-known hydrophilic MXene materials, the MXene foams surprisingly exhibit hydrophobic surfaces and outstanding water resistance and durability. More interestingly, a much enhanced EMI-shielding effectiveness of ≈70 dB is achieved for the lightweight MXene foam as compared to its unfoamed film counterpart (53 dB) due to the highly efficient wave attenuation in the favorable porous structure. Therefore, the hydrophobic, flexible, and lightweight MXene foam with an excellent EMI-shielding performance is highly promising for applications in aerospace and portable and wearable smart electronics.