Cobalt Nanoparticles/Nitrogen-Doped Reduced Graphene Oxide Composite Films for Efficient Electromagnetic Shielding

Free-standing graphene films have garnered widespread interest in electromagnetic interference (EMI) shielding due to their excellent electrical conductivity. However, pure graphene films manifest single electromagnetic loss mechanisms, which constrain their shielding effectiveness. Herein, the cobalt nanoparticle/nitrogen-doped reduced graphene oxide (CoNPs/N-rGO) composite film is synthesized by vacuum-assisted filtration and annealing. The two-dimensional metal–organic framework of cobalt (2D Co-MOF) provides Co and N constituents, and its 2D architecture facilitates the construction of a synergistic conductive network with graphene nanosheets. The abundant Co nanoparticles and N heteroatoms promote magnetic and polarization losses, while the highly conductive network bridged by graphene nanosheets enhances multiple reflections and conduction losses. Owing to multiple loss mechanisms, the EMI shielding effectiveness (SE) of the 27 μm CoNPs/N-rGO composite film reaches 33.5 dB (X-band), which is comparable to the EMI SE simulated by the CST Microwave Studio. The absolute shielding efficiency of the film reaches up to 28,787.5 dB/cm²·g, surpassing that of most graphene materials. Moreover, the PDMS-encapsulated CoNPs/N-rGO composite film demonstrates exceptional shielding stability, maintaining an EMI SE retention rate of up to 93% under acidic and alkaline environments, ultrasonic treatment, and 500 bending cycles. This research offers a straightforward method for designing stable and efficient shielding films suitable for wearable electronic devices and civilian electromagnetic protection fields.