Dual-template hydrothermal synthesis of multi-channel porous NiCo2O4 hollow spheres as high-performance electromagnetic wave absorber

•NiCo2O4 with different morphologies have been successfully synthesized;•The multi-channel porous hollow spheres displayed the superior performance;•The effective bandwidth is up to 5.44 GHz with thin thickness of 1.8 mm;•It is ascribed to the unique multi-channel porous hollow spheres.