Highly sensitive, robust and anisotropic MXene aerogels for efficient broadband microwave absorption

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.