Tailoring of N-doped graphite coated cobalt nanoparticles via arc discharge enables the high microwave absorption

Abstract

Nitrogen-doped graphite-encapsulated cobalt nanoparticles (Co@G NPs) were fabricated via a one-step arc-discharge method. The core/shell nanostructure and surface functionality were tailored by changing the ammonia content in the working gas mixture. Specifically, the average core diameter changed from 5 to 23 nm, average graphite shell thickness from 1.5 to 3.5 nm as the NH3 ratio increased from 0% to 20%. All these arc products exhibited better microwave absorption properties than the pristine Co micro powders. Co@G NPs prepared with 5% of NH3 presented 1.5 at.% of surface doping nitrogen, showing the optimal reflection loss (RL) value of −37.70 dB at the thickness of 5 mm. For the products prepared with 12.5% of NH3, wide absorption bandwidths of 5.60 GHz (RL < −10 dB) and 1.55 GHz (RL < −20 dB) were achieved. The enhancing electromagnetic loss could be attributed to the proper impedance match of dielectric loss (conductance loss, dielectric relaxation (dipolar polarization) and space-charge polarization) and magnetic loss (the eddy current loss, magnetic hysteresis loss and residual loss). This work unlocked an open platform for the facile fabrication of new generation microwave absorbers with light, thin, strong and wide characteristics.