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[Display omitted] • 1. An anion substitution strategy is employed to improve conductivity and dielectric property. • 2. The type of anionic elements has a great influence on the EM wave absorption performance. • 3. NiCo 2 Se 4 and NiCo 2 Te 4 are reported for the first time in the field of EM wave absorption. With the extensive development of electrical communication equipment, the requirements for electromagnetic (EM) wave absorption materials have become more stringent to eliminate electromagnetic interference issues. Rational regulation of permittivity is an efficacious path to optimal EM wave absorption performance. NiCo based spinel materials (NiCo 2 X 4 , X = O, S, Se, Te) have been regarded as promising EM wave absorbing materials due to the advantage of controllable structure, inexpensive procedure and excellent dielectric property. Particularly, the element of anionic sites acts as a considerable role in determining the conductivity and permittivity of materials. Herein, spiny globose like NiCo 2 X 4 (X = O, S, Se, Te) are successfully prepared through hydrothermal and subsequent oxidation, sulfidation, selenization and tellurization methods, respectively. Due to the difference in electronegativity of the anion site elements, NiCo 2 Se 4 and NiCo 2 Te 4 show ameliorative conductivity and dielectric loss. An optimal reflection loss (RL) of −78.5 dB at 2.8 mm and an effective absorption bandwidth (EAB) of 5.28 GHz at 2.3 mm can be achieved for NiCo 2 Se 4. Moreover, due to enhanced dielectric performance, the matching thickness of NiCo 2 Te 4 is greatly improved, which the RL is −54.3 dB at 1.8 mm and EAB of 4.88 GHz at 1.6 mm. The synthesis of NiCo 2 Se 4 and NiCo 2 Te 4 , with remarkable absorption performance, is expected to provide an important reference for broadening the application of NiCo-based spinel in the field of EM wave absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 2D MXene-based accordion-like hybrid structure was obtained. • Controlling the addition of Ti 3 C 2 T x can effectively control the dielectric parameters. • The effective bandwidth is up to 4.24 GHz with a matched thickness of 1.5 mm. Owing to their unique structure and high dielectric loss, two-dimensional transition metal carbides and nitrides (MXenes) are widely used in electromagnetic wave absorption. The novel Co 9 S 8 /C/Ti 3 C 2 T x hybrid material with a multilayer structure was successfully fabricated by hydrothermal and annealing processes. The unique multilayered hybrid material is assembled from Ti 3 C 2 T x film layers, Co 9 S 8 particles, and carbon flakes. The Co 9 S 8 particles were uniformly anchored on Ti 3 C 2 T x and carbon flakes. The Co 9 S 8 /C/Ti 3 C 2 T x -100 hybrid material has demonstrated impressive electromagnetic absorption performance after the multi-component introduction and interface design were optimized. Besides, the hybrid material exhibits the maximum reflection loss of −50.07 dB at 7.6 GHz under a matched thickness of 2.51 mm, and the effective absorption bandwidth (RL ≤ -10 dB) is covered 4.24 GHz. The synergistic effect of dielectric and magnetic loss, interfacial polarization, and multilayer structure was beneficial to the improvement of electromagnetic wave absorption performance. This research provides a simple demonstration of the design and synthesis of high-performance MXenes-based absorbing materials. [ABSTRACT FROM AUTHOR]