Search

A kind of Co-N-C catalysts with hollow core-shell structures with large amount of carbon nano tubes (CNTs) growing on the surface were prepared, using polystyrene (PS) spheres as sacrificial templates, ZIF-8 @ZIF-67 as Co-N-C source and PVP as binder, and their performances in oxygen reduction reaction (ORR) were further explored. The electrochemical test results show that the prepared electrocatalyst Co/NHCNT-160 has good catalytic activity for ORR process and a nearly four-electron reaction path. Co/NHCNT-160 has long-term stability at high onset potential (0.955 V), half-wave potential (0.88 V) and limiting current density (6.3 mA cm−2), with a current retention rate of 99.7 % after 7 h. The ORR performance of Co/NHCNT-160 has surpassed that of commercially available Pt/C catalyst and most of the non-precious metal catalysts reported to date. Its excellent ORR catalytic performance is mainly due to its unique hollow core-shell structure and the abundance of CNTs spawned, the high degree of graphitization facilitating electron migration, the graded pores facilitating mass migration, and the functionalization of the Co-Nx active site with a highly dispersed carbon backbone. This catalyst preparation strategy will provide some ideas for the development of other ZIF-based ORR catalysts for energy storage and electrochemical devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Development of low-cost and high-efficient oxygen reduction reaction (ORR) catalyst is a crucial challenge in fuel cell technology. Herein, we proposed a simple and scalable strategy to fabricate an interconnected 3D Fe 3 O 4 /rGO composite, in which Fe 3 O 4 nanoparticles mechanically anchor in reduced graphene oxide (rGO). Benefiting from its 3D layered structure with loose skeleton and rich porosity, and strong synergetic coupling between Fe 3 O 4 nanoparticles and rGO, the prepared composite, Fe 3 O 4 /rGO, provides better catalytic performance for ORR compared with commercial Pt/C catalyst, featuring high limiting current density (4.6 mA cm−2) close to that of Pt/C (4.7 mA cm−2), low H 2 O 2 yield (1%–6%), high electron transfer number (∼4), and outstanding long-term durability and methanol resistance in alkaline electrolytes. These encouraging results manifest that the Fe 3 O 4 /rGO composite holds great promise as a low-cost and high-performance alternative catalyst for ORR. • Simple and effective method to prepare 3D structured Fe 3 O 4 /rGO as ORR catalyst. • Fe 3 O 4 /rGO has a 3D layered structure with loose skeleton and rich porosity. • Fe 3 O 4 with an average particle size of about 20 nm uniformly anchored on graphene. • Fe 3 O 4 /rGO shows similar catalytic activity and better stability compared with Pt/C. [ABSTRACT FROM AUTHOR]

• A facile epitaxial growth-pyrolysis tactic is proposed. • Highly porous and hollow non-noble metal carbon nanoarchitecture has been constructed. • The N-rich carbon protective layers embedded with cobalt nanoparticles boost the stability of the catalyst. • The Co@N-CNT-HC shows superior electrocatalytic activity for ORR. Fuel cells have emerged as a charming candidate for next-generation energy conversion devices. However, it is highly desired but challenging to engineer advanced non-precious oxygen reduction catalysts with highly actives and stability due to the sluggish kinetics of oxygen reduction reaction (ORR) on fuel cell cathode. Herein, a novel hybrid architecture with Co nanoparticles embedded in N-doped carbon nanotubes and hollow nanocarbon polyhedron (Co@N-CNT-HC) was constructed from core-shell ZIF-67@ZIF-8 via a facile epitaxial growth-pyrolysis process. With the Co@N-CNT-HC as the catalyst, a remarkable ORR performance is achieved in terms of a high half-wave potential of 0.84 V, a large limiting current density of 4.70 mA/cm2, and excellent long-term durability (97.8% current retention after 8 h) in alkaline medium, which outperform commercial Pt/C catalyst. Further dynamic calculations indicated that ORR follows a four-electron reaction mechanism. The enhancement activity of Co@N-CNT-HC is mainly due to the effective integration of 0D Co nanoparticles, 1D carbon nanotubes and 3D hollow nanocarbon, which synergistically strengthen the interfacial reaction kinetics of oxygen and accelerate mass/charge transfer. The strategy reported in this work provides a new insight to synthesis of low-cost and well-designed carbon hybrid electrocatalyst for ORR. [ABSTRACT FROM AUTHOR]

• Highly ordered hexgonal mesoporous TiO 2 -Al 2 O 3 have been synthesized. • TiO 2 content affects the morphology of both TiO 2 -Al 2 O 3 crystals and the mesopores. • The MSI has been modulated by the incorporated TiO 2 species. • TiO 2 promotes the formation of "Type II" NiMoS phases. • The enhanced HDS activity mainly contributed by the enhanced HYDS activity. Highly ordered mesoporous TiO 2 -Al 2 O 3 composites with different TiO 2 mass contents (MA-xTi) were successfully synthesized via an improved solvent evaporation-induced self-assembly method and the corresponding NiMo supported hydrodesulfurization (HDS) catalysts were prepared via wetness incipient co-impregnation method. The materials were characterized by means of XRD, ICP-OES, N 2 physical adsorption-desorption, SEM, TEM, Py-FTIR, H 2 -TPR, HRTEM and XPS and the catalytic activities for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS over the prepared NiMo/MA-xTi series catalysts were investigated. The results show that the crystal forms, crystal morphologies, pore structures, pore arrangements and acidity properties of the MA-xTi samples varied with the incorporation and increase of TiO 2 species; the interaction between the active metals and the support materials (MSI) can be modulated by the incorporation of TiO 2 species, and TiO 2 incorporation also can promote the formation of the so-called "Type II" NiMoS active phase via changing the morphology of Ni promoted MoS 2 slabs, promoting the sulfidation of both Ni and Mo species and enhancing the proportion of NiMoS phase. The catalytic evaluation results show that the enhancement in the overall HDS activity of the NiMo/MA-xTi series catalysts were mainly contributed by the enhancement in the hydrogenation desulfurization (HYDS) activity. Catalyst NiMo/MA-20Ti exhibited the superior catalytic performance due to its highly ordered mesopore arrangement, proper acidity, moderate MSI, moderate stacking and high proportion of NiMoS phase which leads to more highly active "Type II" active sites. [ABSTRACT FROM AUTHOR]