Cellulose nanofiber/MXene/FeCo composites with gradient structure for highly absorbed electromagnetic interference shielding

Conductive polymer composites (CPCs) had attracted tremendous attention in the field of electromagnetic interference (EMI) shielding. However, these materials encountered an intrinsic contradiction between high EMI shielding effectiveness (EMI SE) and low electromagnetic waves reflection. Herein, an excellent EMI SE and low electromagnetic waves reflection composite film with a controllable magnetic-conductive dual gradient structure was constructed using cellulose nanofiber (CNF), MXene, and FeCo by layer-by-layer vacuum filtration method. Benefiting from the synergy of the transition layers and reflection layer with gradient structure, the composite film exhibited favorable impedance matching, abundant loss mechanism, and efficient EMI shielding ability, resulting in absorption dominated shielding characteristic. In addition, the gradient structure facilitated the "absorb-reflect-reabsorb" process when electromagnetic waves were transmitted into the composite film. The obtained CNF/MXene/FeCo-G composite film possessed a remarkable EMI SE of 58.0 dB and the reflection coefficient (R) as low as 0.61. It was proven that the electromagnetic waves absorbing ability can be enhanced by thickening the transition layers, and the EMI SE was improved with the thickening of the reflection layer. Therefore, this work provided a facile strategy to prepare high EMI SE materials with low reflection, which had a good application prospect as the new-generated smart electronic devices.