The increasing need for electromagnetic interference (EMI) shielding of electronics in cold environments such as those in aircraft, space exploration, and wearable heaters to avoid hazardous icing conditions or hypothermia requires the development of thin and lightweight EMI shielding materials preferably by absorbing rather than reflecting EM waves while also generating heat through energy-efficient electrothermal conversion. However, it is challenging to achieve absorption-dominant EMI shielding and energy-efficient electrothermal heating simultaneously in a thin and lightweight structure. Here, we develop a heterogeneous composite film comprising a porous multi-walled carbon nanotubes (MWCNTs)/bacterial cellulose (BC) film and an aligned MXene/Ag nanowires (NWs) backing via a sequential vacuum filtration process. The porous film contains random conductive networks of MWCNTs with moderate conductivity while the aligned MXene sheets atop Ag NWs network affords high conductivity in the backing, giving rise to graded electrical conductivity for absorption-dominant EMI shielding. The increasing Ag NW coverage leads to significantly increased electrical conductivity without increasing the EM wave reflection as well as the density and thickness of the film, yielding excellent specific EMI shielding effectiveness (>8500 dB/(g·cm²)), low driving voltage for energy-efficient electrothermal heating (163°C at 2.5 V), and fast response time (60 s) at a low areal density of 0.015 mg/cm². Combining EMI shielding and electrothermal heating, the heterogeneous film developed here are promising contenders for the protection of electronic equipment in low-temperature environment.

Electrically conductive porous structures are ideal candidates for lightweight and absorption-dominant electromagnetic interference (EMI) shielding. In this review, we summarize the recent progress in developing porous composites and structures from emerging two-dimensional (2D) graphene and MXene nanosheets for EMI shielding applications. Important properties contributing to various energy loss mechanisms are probed with a critical discussion on their correlations with EMI shielding performance. Technological approaches to constructing bulk porous structures, such as 2D porous films, three-dimensional (3D) aerogels and foams, and hydrogels, are compared to highlight important material and processing parameters required to achieve optimal microstructures. A comprehensive comparison of EMI shielding performance is also carried out to elucidate the effects of different assembly techniques and microstructures. Distinctive multifunctional applications in adaptive EMI shielding, mechanical force attenuation, thermal management, and wearable devices are introduced, underlining the importance of unique compositions and microstructures of porous composites. The process–structure–property relationships established in this review would offer valuable guidance and insights into the design of lightweight EMI shielding materials.