ABSTRACT
Metal-organic-frameworks (MOFs) derived carbon or nitrogen-doped carbon (NC) materials are usually used as electromagnetic wave (EMW) absorbers. However, the effective control of the composition and structure of composites is still a major challenge for the development of high-performance EMW absorbing materials. In this work, core-shell structure and bimetallic composition Cu/nitrogen doped carbon @Co/ nitrogen doped carbon (Cu/NC@Co/NC) composites were designed and synthesized through the thermal decomposition of Cu-MOF@Co-MOF precursor. Cu/NC@Co/NC composites with different compositions were obtained by changing the ratio of Co-MOF and Cu-MOF. The composite (Cu/NC@Co/NC-3.75) prepared using 3.75 mmol of Co(NO3)2·6H2O exhibits outstanding EMW absorption properties due to the optimized impedance matching and strong attenuation ability, which is caused by enhanced interfacial and dipolar polarization as well as multiple reflection and scattering. With the filler loading in paraffin of 35 wt%, the minimum reflection loss (RLmin) is up to -54.13 dB at 9.84 GHz with a thin thickness of 3 mm, and the effective absorption bandwidth (EAB, RL≤ - 10 dB) reaches 5.19 GHz (10.18-15.37 GHz) with the corresponding thickness of 2.5 mm. Compared with the Cu/NC and Co/NC, the Cu/NC@Co/NC-3.75 composite exhibits much better EMW absorbing performances caused by the bimetallic composition and the unique core-shell structure. This work provides a rational design for MOF-derived lightweight and broadband EMW absorbing materials.
ABSTRACT
Transition-metal compounds/carbon hybrids with high electrocatalytic capability possess attractive potential as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). However, the simple structure and agglomeration always result in poor performance. Herein, cobalt selenides confined in hollow N-doped porous carbon interconnected by carbon nanotubes (CNTs) with cobalt selenides encapsulated inside (denoted as CoSe@NPC/CoSe@CNTs) are formed through in situ pyrolysis and selenization process. In this strategy, ZIF-67 is used as the precursor, structure inducer, and carbon source for the orientated growth of CNTs. Such a rational architecture provides a stable interconnected conductive network and a hierarchically porous structure, with more available active sites and a shortened pathway for charge transport, synergistically enhancing the electrocatalytic activity. Specifically, the DSSCs based on CoSe@NPC/CoSe@CNTs demonstrate a high efficiency of 7.36%, even superior to that of Pt (7.16%). Furthermore, the CoSe@NPC/CoSe@CNT CE also demonstrates a good long-term stability in the iodine-based electrolyte.
