Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti ₃ C ₂ T _x film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti ₃ C ₂ T _x films (4600 Siemens per centimeter) and multiple internal reflections from Ti ₃ C ₂ T _x flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

Free-standing Ti₃C₂T_x MXene/carbon nanofiber electrodes are prepared via electrospinning Ti₃C₂T_x MXene flakes with polyacrylonitrile (PAN) and carbonizing the fiber networks. Using this simple fabrication method, delaminated MXene flakes are embedded within carbon nanofibers and these fiber mats are used as electrodes without binders or additives. Unlike coated electrodes, which may suffer from the active material delaminating from the substrate during folding or bending, composite electrodes are stable and durable. Previous attempts to incorporate Ti₃C₂T_x MXene into electrospun fibers resulted in low mass loadings, ∼1 wt% Ti₃C₂T_x MXene. In this work, MXene flakes are added into PAN solutions at a weight ratio of 2 : 1 (MXene : PAN) in the spinning dope, producing fiber mats with up to 35 wt% MXene. Composite electrodes have high areal capacitance, up to 205 mF cm⁻² at 50 mV s⁻¹, almost three times that of pure carbonized PAN nanofibers (70 mF cm⁻² at 50 mV s⁻¹). Compared with electrospun nanofibers spray-coated with Ti₃C₂T_x, these composite fibers exhibit double the areal capacitance at 10 mV s⁻¹. This method can be used to produce MXene composite fibers using a variety of polymers, which have potential applications beyond energy storage, including filtration, adsorption, and electrocatalysis, where fibers with high aspect ratio, accessible surface, and porosity are desirable.