(618g) Multilevel Structured Electrospun Ceramic Nanofibers and Their Potential Applications in the Energy Sector | AIChE

(618g) Multilevel Structured Electrospun Ceramic Nanofibers and Their Potential Applications in the Energy Sector


Grader, G. S. - Presenter, Technion - Israel Institute of Technology
Elishav, O., Technion - Israel Institute of Technology
Shter, G. E., Technion - Israel Institute of Technology
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oren eli Normal oren eli 1 1 2019-04-06T06:25:00Z 2019-04-06T06:26:00Z 2 555 3169 26 7 3717 16.00

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embed">The ability to design ceramic nanofibers with complex
morphology and specific chemical and physical properties is highly desirable for
advanced energy applications. Furthermore, large and self-supporting nanofiber mats
can circumvent many of the problems with nanoparticle processing that pose
technical and health difficulties. Surface and inner multilevel architecture such
as porous and hollow nanofibers can reduce mass transport limitation, which is
needed to achieve improved performance.

embed">Electrospinning offers a simple way to produce
continuous nanofibers with controlled morphology over diverse materials
including polymers, metals, ceramics and composites. Electrospinning is cost
effective and suitable for large-scale industrial productions. The basic setup
consists of a high voltage power supply, metallic needle, grounded or negative
charged collector and syringe pump. In electrospinning, a large electric field
(typically in the range of 5 to 30 kV) is applied to a viscous droplet. Beyond
a threshold voltage, the surface tension of the solution is overcome, forming a
charged jet, which is attracted to the collector. During the process, the
liquid jet undergoes considerable stretching and elongation while solvent
evaporation occurs simultaneously. These effects give rise to a significant
decrease in fiber diameter from few microns down to hundreds or tens of
nanometers, depending mainly on the solution viscosity and electrospinning
parameters. A number of process and solution
parameters govern the electrospinning behavior, providing versatility in the
final fiber diameter and morphology. The resulting fibrous mat can be composed
of a non-woven random arrangement of fibers or aligned, uniform nanofibers,
depending on the collector design.

embed">In ceramic nanofibers, usually the electrospinning
stage is typically followed by thermal treatment to remove the polymer and
obtain the final structure and phase. This step often includes shrinkage,
potential deleterious deformation, and phase and morphologies changes. Thus, one
of the most important aspects of ceramic nanofibers is their final morphology. Unique
Fe-Al-O lamellar-like porous surface nanofibers (Figure. 1) were synthesized as
catalysts for carbon dioxide hydrogenation to liquid fuels. The structure is
obtained by reordering of an initially uniform fibers consisting of two metals
coordination complexes (Al/Fe(acac)3) and
a polymer. A general mechanism for the morphology formation is suggested, where
the final structure depends on deformation processes during thermal treatment. The
relation between morphology and catalytic performance will be discussed.

embed">The mechanism is realized in several other material
systems such as Ti-Al-O, Fe2O3,
Ni-Al-O and Al2O3, providing similar structure but
different functionalities. Thus, the formation mechanism is general and can be
implemented to other materials opening new research directions. For instance,
in nickel-based system these unique nanofibers were examined as lithium-ion
anodes and showed promising performance.


ltr;unicode-bidi:embed">Figure 1. HRSEM images of lamellar-like
Fe-Al-O nanofibers

embed">In addition, control of the inner multilevel structure of
the fiber as a function of sample thickness, composition and heat rate
conditions is described in the Fe-Al-O system. The transformation mechanism from
solid to hollow nanofibers and nanobelts is outlined, explaining the formation
of these structures. The obtained results establish the basic understanding of
the interplay between the process conditions and the nanofibers’ complex surface
morphology and inner multilevel structure required for heterogeneous catalysts
and electrodes.


ltr;unicode-bidi:embed">Figure 2. HRSEM images of Fe-Al-O hallow