Cu2+ induced self-assembly of urchin-like Co1−xCux into hollow microspheres toward wideband and thin microwave absorbers

Abstract Regulating the structure and ingredients of hollow structures can solve the problems of thickness, heaviness, and narrow broadband faced by metal microwave absorbers. Herein, we have developed for the first time a facile one-pot hydrothermal reduction approach to selectively preparing bimetallic Co1–xCux (x = 0, 0.012, 0.031, 0.062, 0.125, 0.250, 0.498) hollow microspheres (HMs) consisting of urchin-like superstructures. The selective adsorption of surfactants and prenucleated Cu seeds guide the growth of Co into 1D rods, which subsequently assembled into urchin-like Co1−xCux superstructures and further into HMs driven by the minimization of magnetic anisotropic energy or surface free energy. The combination of Co with Cu into Co1–xCux HMs can tune the structure, size, defect, components, conductivity, and magnetic properties. Moreover, urchin-like Co1−xCux HMs consisting of sparse rods with low Cu content (1%) and large diameter (5–10 µm) benefit the excellent absorption capacity by producing good impedance matching, multiple losses, and electrical/magnetic coupling effects. Interestingly, the Co0.990Cu0.010 HMs exhibited a stronger absorption (−37.94 dB), a wider bandwidth (9.68 GHz), a lower loading (30 wt%), and a smaller matching thickness (1.3 mm) compared with other absorbers. Our findings suggest that the Co1–xCux HMs will perform well as a superior absorber for EM wave absorption and shielding applications due to the adjustable saturation magnetization and outstanding absorption capacity.