Supplement Number 1

See the supplementary material for the details of the synthesis procedures of HE-MAX, HE-M-MXene, and HE-FMXene; the Rietveld refinement of XRD patterns; SEM images; SEM-EDX elemental mapping and spectra; XPS, FTIR, EPR and AFM characterizations; XPS peak fitting results for HE-MAX and HE-F-MXene (Table S1); schematic illustrations of electromagnetic (EM) wave absorption mechanisms; and microwave absorption performance including RL curves; |Zin/Z0| matching; and effective absorption bandwidth (EAB) comparisons; and comparative data of microwave absorption performance for various related materials (Table S2).