Ni Nanoparticle‐Decorated Reduced Graphene Oxide Hybrids With Tunable Dielectric–Magnetic Synergy for Efficient Microwave Absorption

ABSTRACT Reduced graphene oxide (rGO)‐based microwave absorbers generally exhibit strong dielectric attenuation but unsatisfactory impedance matching, while simply increasing the magnetic‐component loading does not necessarily improve microwave absorption. Herein, Ni nanoparticle‐decorated rGO hybrids were prepared through coprecipitation followed by chemical vapor deposition‐assisted thermal reduction. A dual‐comparison framework combining Ni‐loading‐state regulation and same‐precursor NiO‐to‐Ni phase evolution was employed to clarify the relationships among nanoparticle dispersion, phase composition, electromagnetic response, and microwave absorption performance. Increasing the initial Ni precursor concentration increased the mean Ni nanoparticle size from 23.25 to 25.48 and 29.98 nm and promoted more pronounced aggregation, whereas the absorption performance exhibited a nonmonotonic dependence on the nominal Ni loading. For the optimized rGO/Ni‐5 hybrid, the Ni content was estimated to be approximately 32.6 wt.% by thermogravimetric analysis and 30.36 wt.% by semi‐quantitative energy‐dispersive X‐ray spectroscopy analysis. At a filler loading of 15 wt.%, rGO/Ni‐5 achieved a minimum reflection loss of −35.5 dB at 8.4 GHz with a thickness of 3.0 mm and an effective absorption bandwidth of 3.28 GHz from 9.52 to 12.80 GHz at 2.3 mm. Vibrating sample magnetometer measurements showed that rGO/Ni‐5 exhibited the strongest static magnetic response among the investigated rGO/Ni hybrids, while radar cross‐section simulations demonstrated reduced electromagnetic scattering compared with pure rGO and the rGO/NiO‐5 phase control. These results indicate that the superior performance of rGO/Ni‐5 originates from the coordinated regulation of nanoparticle dispersion, phase composition, dielectric–magnetic response, impedance matching, and attenuation capability, rather than from simply maximizing Ni loading or any individual loss parameter.