Adjustable Humidity Response: Ultrahigh Green EMI Shielding Gel with Double‐Side Constant Temperature Capability

Abstract With the increasingly serious secondary pollution of electromagnetic waves (EMWs), efficient green shielding materials have become an urgent need. MXene is widely used in electromagnetic interference (EMI) shielding due to its large surface area and high conductivity. Here, this work constructs MXene islands with better shielding performance through viscosity control and continuous mechanical stirring. Benefiting from the MXene islands, Janus‐structural gel with humidity response is successfully prepared, showing controllable ultrahigh green shielding property (up to 100.5 dB, thickness of 2 mm). Interestingly, this gel can spontaneously adjust its water content according to the humidity, resulting in a reversible transformation in three states to meet the needs of different environments. By Janus‐structural design and reasonable material combination, this gel demonstrates excellent electrothermal (rise to 111.6 °C, 5 s, 2 V)/thermal insulation (thermal conductivity is low to 0.029 W m −1 K −1 ) properties to meet the needs of shielding in underwater/fire operations.