Dielectric-dielectric nanocomposites with excellent synergistic effects are considered as a prospective avenue for the development of high-performance microwave absorbers. In this work, one-dimensional MoO 2 /Mo 2 C/C heterogeneous nanowires were synthesized via a straightforward co-precipitation and in situ pyrolysis process. The components were modulated by adjusting the reduction temperatures to achieve tunable electromagnetic parameters thereby optimizing the dielectric loss. The results showed that the optimized MoO 2 /Mo 2 C/C composite exhibited a minimum reflection loss of −50.7 dB at an ultra-thin thickness of 1.8 mm and an effective absorption bandwidth of 6 GHz at 2.3 mm when the calcination temperature was 700 °C. Based on the studies of electromagnetic parameters and radar cross section simulation outcomes, both the interwoven one-dimensional structure and synergistic effects between the components have endowed the material with good impedance matching and introduced various loss mechanisms such as conductivity loss, multiple polarization relaxation, and multiple reflection/scattering. This work presented a viable strategy for the preparation of one-dimensional MoO 2 -based dielectric microwave absorption materials.
Jieyu Xu,Lin Ge,Yajun Zhou,Guangyu Jiang,Liang Li,Yunheng Li,Yongsheng Li
Heteroatom doping has been proved to be an effective strategy to optimize the activity of hydrogen evolution reaction (HER) catalysts. Herein, we report N, P, S multi-doped Mo2C/C composites exhibiting highly efficient HER performance in acidic solution, which are facilely fabricated via annealing of N, P, S-containing MoOx–polyaniline (MoOx–PANI) hybrid precursors. The optimized N, P, S multi-doped Mo2C/C catalyst with a moderate P dopant level (NPS-Mo2C/C-0.5) exhibits excellent performance with an overpotential of 53 mV to achieve a current density of 20 mA cm−2, a Tafel slope of 72 mV dec−1 and good stability in acidic electrolytes. Based on the study of XPS, EPR and 31P MAS NMR, the excellent electrocatalytic performance could be attributed to the effective electronic configuration modulation of both Mo2C nanorods and the carbon matrix, derived from stronger synergistic N, P, S multi-doping coupling effects. This work provides a promising methodology for the design and fabrication of multi-doped transition metal based electrocatalysts via electronic structure engineering.
A strategy was proposed for the synthesis of Mo 2 C/C composite as an efficient electrocatalyst through electrospinning and calcination. PVP and PAN were utilized as electrospinning precursors for comparative analysis. Morphological characterization revealed that an electrospinning solution with the viscosity in the range of 2–5 mPa·S was conducive to the formation of spherical morphology. Under calcination at nitrogen atmosphere, as-electrospun Mo@PVP-1 and Mo@PAN-1 samples transformed into Mo 2 C/C with bead-like structure at 900 and 800 °C, respectively. Compared to PVP, PAN exhibited greater resistance to deformation at elevated temperature, resulting in better-dispersed spherical Mo 2 C/C composite. The synthesized Mo 2 C/C exhibited good electrocatalytic activity for hydrogen evolution reaction. The Tafel slopes of Mo 2 C/C prepared from Mo@PVP-1-900 and Mo@PAN-1-800 were 75.85 and 164.7 mV·dec −1 , respectively. This work contributes to the understanding of synthetic process of spherical Mo 2 C/C composites through electrospinning, providing an effective way to improve material performance. Graphical Mo 2 C/C composites were synthesized by calcination with different polymer solutions (PAN and PVP) by electrostatic spraying, and their performance as catalysts was tested.
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