Synthesizing lightweight, thin–profile, and high–performance microwave absorbers has emerged as an urgent research topic. A promising strategy for carbon–based materials to achieve these attributes is to rationally construct heterostructures. Herein, 0.89–1.54 at.% nitrogen(N)–doped carbon onion nanotube chains (NCONCs) were produced by blending CONCs harvested from candle combustion with HH 4 Cl and subjecting them to heating at 300–400 °C for 3 h. The hinge–like NCONCs revealed numerous electron transport paths, facilitating the formation of multi–tiered conduction networks. The N–doping introduced C–N groups and interfaces into the CONCs, which yielded extensive dipole and interfacial polarization. Simultaneously, the 1.14 at.% N–doping endowed NCONC–400 with suitable conductivity, thereby ensuring excellent impedance matching. The resulting synergistic effect of impedance matching and electromagnetic wave attenuation was clearly observed. Specifically, NCONC–400 exhibited exceptional performance with a maximum effective absorption bandwidth of 4.71 GHz and a peak reflection loss of –35.47 dB at 1.4 mm. The radar cross–section reduction demonstrated by NCONC–400 composites reached 21.43 dB cm 2 . These impressive results prove the distinctive advantages of CONCs in tailoring performance and optimizing impedance matching, which are appealing for lightweight and efficient microwave absorbers.
Optimizing platinum-based catalysts for hydrogen generation via water electrolysis in pH-universal electrolytes is significant, and modulating the electronic structure is a viable strategy. Herein, platinum-iron (Pt–Fe) alloys with varying composition supported on carbon onions (CNOs) were successfully synthesized: Pt x Fe y @CNOs (x, y = 0.6, 0.4; 0.5, 0.5; 0.4, 0.6). Beneficial from the precisely modulated crystal plane spacing and electronic structure by tuning the Pt/Fe composition, in general pH electrolytes, Pt x Fe y @CNOs display outstanding hydrogen evolution reaction (HER) activity. The as-prepared Pt 0.5 Fe 0.5 @CNOs shows low overpotentials (η 10 ) of 11, 30, and 19 mV at −10 mA cm −2 in 0.5 M H 2 SO 4 , 1.0 M phosphate-buffered saline (PBS), and 1.0 M KOH electrolyte, respectively. Compared to commercial Pt/C, it displays enduring stability up to 24 h. Density functional theory (DFT) calculations indicate that Pt 0.5 Fe 0.5 @CNOs displays the lowest H* Gibbs free energy (ΔG H* ) and water dissociation energy values, due to the suitable proton adsorption and H 2 O dissociation processes offered by its electronic structure. Moreover, it is proven that the support with better wettability has a positive effect on HER performance of the catalyst. The optimal electronic structure and improved wettability provide novel insight into developing a Pt-based HER pH-universal catalyst.
Yuqi Yan,Qinghai Ma,Fang Cui,Jiajia Zhang,Tieyu Cui
High-performance carbon onions coated Ni/NiO nanoparticles (CNN NPs) acting as electrocatalysts in alkaline hydrogen evolution reaction (HER) is synthesized base on a self-assembly process combined with a calcination process. By systematically regulating the surface composition, we find that controlling the kinetic steps in HER by regulating the ratio of Ni/NiO can significantly promote alkaline HER activity, and CNN-500 with a Ni/NiO ratio of 1.31 display an overpotential of 127 mV (vs. RHE) at a current density of 10 mA cm −2 for HER in 1 M KOH electrolyte. The ratio of Ni and NiO active catalytic components are adjustable via controlling the calcination process, which play an important role in alkaline HER performance. Due to the synergistic effect between Ni, NiO and C, the CNN-500 shows superior intrinsic catalytic activity than that of currently reported HER electrocatalysts. This work provides a facile and useful strategy to get high-performance alkaline HER electrocatalysts for hydrogen energy source.
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