Multifunctional Asymmetric Bilayer Aerogels for Highly Efficient Electromagnetic Interference Shielding with Ultrahigh Electromagnetic Wave Absorption

Abstract

Although multifunctional electromagnetic interference (EMI) shielding materials with ultrahigh electromagnetic wave absorption are highly required to solve increasingly serious electromagnetic radiation and pollution and meet multi-scenario applications, EMI shielding materials usually cause a lot of reflection and have a single function. To realize the broadband absorption-dominated EMI shielding via absorption–reflection–reabsorption mechanisms and the interference cancelation effect, multifunctional asymmetric bilayer aerogels are designed by sequential printing of a MXene-graphene oxide (MG) layer with a MG emulsion ink and a conductive MXene layer with a MXene ink and subsequent freeze-drying for generating and solidifying numerous pores in the aerogels. The top MG layer of the asymmetric bilayer aerogel optimizes impedance matching and achieves re-absorption, while the bottom MXene layer enhances the reflection of the incident electromagnetic waves. As a result, the asymmetric bilayer aerogel achieves an average absorption coefficient of 0.95 in the X-band and shows the tunable absorption ability to electromagnetic wave in the ultrawide band from 8.2 to 40 GHz. Finite element simulations substantiate the effectiveness of the asymmetric bilayer aerogel for electromagnetic wave absorption. The multifunctional bilayer aerogels exhibit hydrophobicity, thermal insulation and Joule heating capacities and are efficient in solar-thermal/electric heating, infrared stealth, and clean-up of spilled oil.

1. Introduction

Serious electromagnetic interference (EMI) and radiation adversely affect normal operation and even cause severe malfunctions of electronic devices, and the electronic devices can also be easily detected by using advanced multi-spectrum detection techniques [1, 2]. Electrically conductive transition metal carbonitride (MXene) sheets with abundant surface functional groups have attracted much attention because of their remarkable electrical conductivity, high specific surface area, and ease of process in aqueous media [3, 4]. In particular, conductive MXene-based aerogels with high porosity, rich interfaces, and low density are promising for EMI shielding [5–8], electromagnetic wave absorption [9–11], thermal insulation [12], oil adsorption [13], energy storage [14, 15], and sensing [16, 17]. Currently, unifunctional MXene aerogels have their limitations in complex and variable application environments [18–20]. It is now imperative to design multifunctional MXene aerogels and expand their application scenarios [21, 22].

The structural design is crucial for achieving satisfactory EMI shielding performances of conductive MXene-based materials and architectures used in diverse scenarios [23, 24]. Generally, when incident electromagnetic waves encounter a conductive material surface via a propagating medium, the large impedance mismatch usually causes the reflection of a large proportion of the incident waves, thus causing secondary environmental pollution [25]. In particular, porous MXene aerogels can provide multiple reflection/scattering interfaces in their interiors and extend the propagation paths of electromagnetic waves, thus benefiting the enhancement in electromagnetic wave absorption. Gao et al. reported a silver microtubule/polydimethylsiloxane (PDMS) composite [26], in which the hollow structure of the silver microtubules could enhance multiple reflections of electromagnetic waves, interface polarization, and conduction loss, exhibiting absorption-dominated EMI shielding with an absorption coefficient (A) of 0.79 at 8.2 GHz.

The direct reflection of electromagnetic waves can be weakened by reducing the electrical conductivity of MXene-based materials to achieve impedance matching. Xue et al. fabricated a MXene/carbon nanotube/polyimide aerogel with a gradient conductive structure [27]. Its slightly conductive top layer...