Multishell
hollow nanoarchitectures are one of the most important
branches in the nanomaterial field due to their enormous potential
in many fields, but synthesizing them in a well-controlled manner
remains challenging. Herein, we present a general strategy for the
construction of multishell hollow metal/nitrogen/carbon dodecahedrons
(metal@NC) with well-defined and precisely controlled architectures.
This strategy is based on the pyrolysis of multilayer solid ZIFs prepared
by a step-by-step crystal growth approach, which enables precise control
over the shell number and composition of the resultant hollow metal@NC.
Impressively, our strategy can be further extended to the synthesis
of yolk@multishell hollow structures or multishell hollow structures
that are assembled by carbon nanotubes. The multishell hollow structures
can efficiently facilitate the mass diffusion, which together with
the high dispersity and increased surface area are responsible for
their significantly enhanced catalytic performances for the selective
hydrogenation of biomass-derived furfural to cyclopentanol when compared
with their solid and single-shell counterparts. We anticipate that
our general strategy would shed light on the rational design and accurate
construction of other complex multishell hollow materials for various
important yet challenging applications.
In
order to improve the catalytic performance of oxygen reduction
reaction (ORR), it is pivotal to increase the density and accessibility
of the active sites. Herein, we have developed a template-free melamine-assisted
cocalcined strategy to afford Fe-embedded and N-doped carbons (Fe–N–C)
with not only high density of atomically dispersed Fe–N
x
active sites but also abundant three-dimensional
interconnected mesopores by directly pyrolyzing Fe-ZIF-8 covered with
a controllable melamine layer. It is demonstrated that the introduction
of melamine in the precursor plays a key role in constructing various
carbonized products with controllable morphology, porosity, and components.
With an optimal mass ratio 1:1 of melamine to Fe-ZIF-8, the resultant
Fe@MNC-1 exhibits excellent ORR activity and stability, which exceeds
20 wt % commercial Pt/C catalyst (with a half-wave potential of 0.88
V vs 0.85 V) in an alkaline electrolyte and is even comparable to
the commercial Pt/C catalyst (with a half-wave potential of 0.78 V
vs 0.80 V) in an acidic electrolyte. To the best of our knowledge,
Fe@MNC-1 can be ranked among the best nonprecious metal electrocatalysts
for ORR in both alkaline and acidic media. The present synthetic strategy
may provide a new opportunity for the design and construction of metal–organic
framework-derived nanomaterials with rational composition and a desired
porous structure to boost their electrocatalytic performance.
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