Hollow metal oxides and carbon hybrids with hierarchical and robust nanoarchitecture hold great potential as high-performance electrode materials. Herein, a relatively unexplored hollow and hierarchical metal–organic framework (MOF) assembled by parallel stacked triangular sub-MOFs were successfully synthesized via a facile co-precipitation method. The hollow MOFs were then converted to binary metal oxides@carbon composites, exemplified herein as Zn–Mn mixed oxides@carbon (Zn_xMnO@C) hybrids. The obtained Zn_xMnO@C inherits the unique hollow hexagonal nanodisks (HHNDs) structure of the MOF precursor, and each triangular plate-like subunit consists of a continuous carbon matrix embedded uniformly within the ultrafine Zn_xMnO nanoparticles. When evaluated as an anode material for lithium ion batteries, the Zn_xMnO@C HHNDs exhibited high specific capacity (1050 mA h g⁻¹ at 0.1 A g⁻¹ after 200 cycles) and remarkable cycling performance up to 1000 cycles. It is believed that besides the protection of the carbon matrix, the unique hierarchically hollow structure with parallel stacked subunits endows the Zn_xMnO@C hybrid with additional capability to withstand lithiation/delithiation strain. Moreover, kinetics-analysis based on cyclic voltammograms (CVs) reveals that the high lithium storage capacity is primarily attributed to fast kinetics originating from pseudocapacitive contribution. This also accounts for the good rate capabilities of Zn_xMnO@C HHNDs (713 and 330 mA h g⁻¹ at 1 and 10 A g⁻¹, respectively). Furthermore, full cells with Zn_0.5MnO@C anodes and LiMn₂O₄ cathodes are assembled and show good cycling stability over 120 cycles. This study demonstrates a new hollow structure of MOFs and its usefulness in developing robust and hierarchical metal oxide/carbon composites for electrochemical storage applications.

Tunable electromagnetic properties and excellent thermo-stability are important criteria while choosing absorbers. Here, carbon-coated Fe₃Si nanoparticles in amorphous SiCO ceramics (SiCO/C/Fe₃Si) were successfully obtained via polymer-derived ceramics (PDC) from ferric acetylacetonate modified-polysilylacetylene (PSA). By adjusting the magnetic components, the structure of the absorbers could be tuned and their bandwidth varied. The absorbers with a hybrid composition (4.35 wt% Fe) possessed a minimal reflection loss (RL) of −32 dB at 9.2 GHz with a thickness of 3.5 mm and an effective bandwidth (RL < −10 dB) of about 3.6 GHz. The absorbers (12.33 wt% Fe) were enhanced and the minimal RL value was close to −41 dB at 7.9 GHz with a thickness of 3.5 mm. Simultaneously, a broad bandwidth (RL < −5 dB) appeared and covered nearly the whole S-band (2–3.95 GHz) where the RL value reached −10 dB at 2 GHz. After the second thermal treatment under 1000 °C, the minimal RL value of the absorbers (12.33 wt% Fe) remained at −33 dB at 6.6 GHz with a thickness of 4 mm, while the effective bandwidth was 3.4 GHz with a thickness of 3 mm. In addition, the formation mechanism of carbon-coated Fe₃Si, which possibly resulted from the mesophase SiCFe alloy was also discussed. The as-prepared SiCO/C/Fe₃Si hybrid exhibits outstanding wave absorption ability and present a huge potential for the application at high temperatures.