A Study on the Effects of Carrier Gases on the Structure and Morphology of Carbon Nanotubes Prepared by Pyrolysis of Ferrocene and C_2H_2 Mixture

Carbon nanotubes (CNTs) were prepared using different carrier gases, with ferrocene as the catalyst precusor and acetylene as the carbon source. The effects of ammonia and nitrogen as carrier gases on the structure and morphology of CNTs were investigated. Transmission electron microscope (TEM), high-resolution electron microscope (HRTEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to characterize the products and the catalyst. Experiment results show that the CNTs grown in N2 gas exhibited cylindrical and tubular structure, while a bamboo-like structure was observed for the CNTs grown in NH3 gas. Moreover, vertically aligned CNTs were obtained on an Al2O3 disk when NH3 was used as the carrier gas. The carrier gas also exerted influence on the shape of the catalyst. Based on the theory of active centers of catalysis and combined with the particle shape of the catalyst, a growth model for the vertically aligned CNTs on the substrate is given.

Single-atomic Mn sites coupled with Fe_(3)C nanoparticles encapsulated in carbon matrixes derived from bimetallic Mn/Fe polyphthalocyanine conjugated polymer networks for accelerating electrocatalytic oxygen reduction

The construction of robust coupling catalysts for accelerating electrocatalytic oxygen reduction reaction(ORR)through the modulation of the electronic structure and local atomic configuration is critical but remains challenging.Herein,we report a facile and effective isolation-polymerization-pyrolysis(IPP)strategy for high-precision synthesis of single-atomic Mn sites coupled with Fe_(3)C nanoparticles encapsulated in N-doped porous carbon matrixes(Mn SAs/Fe_(3)C NPs@NPC)catalyst derived from predesigned bimetallic Fe/Mn polyphthalocyanine(FeMn-BPPc)conjugated polymer networks by solid-phase reaction approach.Benefiting from the synergistic effects between the single-atomic Mn-N_(4)sites and Fe_(3)C NPs as well as the confinement effect of NPC,the Mn SAs/Fe_(3)C NPs@NPC catalyst exhibited excellent electrocatalytic activity and stability for ORR.The assembled Znair battery displayed larger power density of 186 mW·cm^(−2)than that of Pt/C+Ir/C-based battery.It also exhibits excellent stability without obvious voltage change after 106 cycles with 36 h.Combing in-situ Raman spectra with in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy(ATR-SEIRAS)characterization results indicated that the Mn-N_(4)site as an active site for the O_(2)adsorption-activation process,which effectively facilitates the generation of key*OOH intermediates and*OH desorption to promote the multielectron reaction kinetics.Theoretical calculation reveals that the excellent electrocatalytic performance originates from the charge redistribution and the d orbital shift resulting from Mn-Fe bond,which buffers the activity of ORR through the electron reservoir capable of electron donation or releasing.This work paves a novel IPP strategy for constructing high-performance coupling electrocatalyst towards the ORR for energy conversion devices.