Single-atom catalysts
(SACs) have attracted widespread interest
for many catalytic applications because of their distinguishing properties.
However, general and scalable synthesis of efficient SACs remains
significantly challenging, which limits their applications. Here we
report an efficient and universal approach to fabricating a series
of high-content metal atoms anchored into hollow nitrogen-doped graphene
frameworks (M-N-Grs; M represents Fe, Co, Ni, Cu, etc.) at gram-scale.
The highly compatible doped ZnO templates, acting as the dispersants
of targeted metal heteroatoms, can react with the incoming gaseous
organic ligands to form doped metal–organic framework thin
shells, whose composition determines the heteroatom species and contents
in M-N-Grs. We achieved over 1.2 atom % (5.85 wt %) metal loading
content, superior oxygen reduction activity over commercial Pt/C catalyst,
and a very high diffusion-limiting current (6.82 mA cm
–2
). Both experimental analyses and theoretical calculations reveal
the oxygen reduction activity sequence of M-N-Grs. Additionally, the
superior performance in Fe-N-Gr is mainly attributed to its unique
electron structure, rich exposed active sites, and robust hollow framework.
This synthesis strategy will stimulate the rapid development of SACs
for diverse energy-related fields.
Tin dioxide (SnO ) has attracted much attention in lithium-ion batteries (LIBs) due to its abundant source, low cost, and high theoretical capacity. However, the large volume variation, irreversible conversion reaction limit its further practical application in next-generation LIBs. Here, a novel solvent-free approach to construct uniform metal-organic framework (MOF) shell-derived carbon confined SnO /Co (SnO /Co@C) nanocubes via a two-step heat treatment is developed. In particular, MOF-coated CoSnO hollow nanocubes are for the first time synthesized as the intermediate product by an extremely simple thermal solid-phase reaction, which is further developed as a general strategy to successfully obtain other uniform MOF-coated metal oxides. The as-synthesized SnO /Co@C nanocubes, when tested as LIB anodes, exhibit a highly reversible discharge capacity of 800 mAh g after 100 cycles at 200 mA g and excellent cycling stability with a retained capacity of 400 mAh g after 1800 cycles at 5 A g . The experimental analyses demonstrate that these excellent performances are mainly ascribed to the delicate structure and a synergistic effect between Co and SnO . This facile synthetic approach will greatly contribute to the development of functional metal oxide-based and MOF-assisted nanostructures in many frontier applications.
A facile and efficient template-free method has been successfully developed to fabricate uniform nitrogen-doped carbon-confined V2O3 hollow spheres, which displayed stable and fast lithium storage.
N-doped
carbon-confined transition metal nanocatalysts display
efficient oxygen reduction reaction (ORR) performance comparable to
commercial Pt/C electrocatalysts because of their efficient charge
transfer from metal atoms to active N sites. However, the sheathed
active sites inside the electrocatalysts and relatively large-size
confined metal particles greatly restrict their activity improvement.
Here, we develop a facile and efficient “MOFs plus ZIFs”
synthesis strategy to successfully construct ultrafine sub-5 nm Co
nanodots confined into superficial N-doped carbon nanowires (Co@C@NC)
via a well-designed synthesis process. The unique synthesis mechanism
is based on low-pressure vapor superassembly of thin zeolitic imidazolate
framework (ZIF) coatings on metal–organic framework substrates.
During the successive pyrolysis, the preferential formation of the
robust N-doped carbon shell from the ZIF-67 shell keeps the core morphology
without shrinkage and limits the growth of Co nanodots. Benefiting
from this architecture with accessible and rich active N sites on
the surface, stable carbon confined architecture, and large surface
area, the Co@C@NC exhibits excellent ORR performance, catching up
to commercial Pt/C. Density functional theory demonstrates that the
confined Co nanodots efficiently enhance the charge density of superficial
active N sites by interfacial charge transfer, thus accelerating the
ORR process.
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