4 research outputs found
Origin of the Volume Contraction during Nanoporous Gold Formation by Dealloying for High-Performance Electrochemical Applications
Nanoporous metals
used in various electrochemical applications
including electrochemical actuators, electrocatalysts, supercapacitors,
and batteries exhibit an irreversible volume shrinkage during their
formation by dealloying, the origin of which remains obscure. Here
we use dilatometry techniques to measure the irreversible shrinkage
in nanoporous Au <i>in situ</i> during electrochemical dealloying.
A linear contraction up to ∼9% was recorded. To identify the
origin of this dimensional change, we borrow the time-dependent isothermal
shrinkage model from sintering theory, which we use to fit the dimensional
changes measured in our nanoporous Au during dealloying. This shrinkage
model suggests that bulk transport through plastic flow is the primary
mass transport mechanism responsible for the material contraction
in dealloying. Based on the current understanding of the mechanism
of porosity formation in dealloying, mass transport through surface
diffusion of undissolved materials is critical in the process. The
present work sheds new light in the sense that bulk transport through
plastic flow seems also to play an important role in dealloying
pH-Controlled Dealloying Route to Hierarchical Bulk Nanoporous Zn Derived from Metastable Alloy for Hydrogen Generation by Hydrolysis of Zn in Neutral Water
Dealloyed
nanoporous metals made of very-reactive elements have rarely been
reported. Instead, reactive materials are used as sacrificial components
in dealloying. The high chemical reactivity of nonprecious nanostructured
metals makes them suitable for a broad range of applications such
as splitting water into H<sub>2</sub> gas and metal hydroxide. On
the other hand, the same high chemical reactivity hinders the synthesis
of nanostructured metals. Here we use a pH-controlled dealloying strategy
to fabricate bulk nanoporous Zn with bulk dimensions in the centimeter
range via the selective removal of Al from metastable face-centered
cubic bulk Zn<sub>20</sub>Al<sub>80</sub> at. % parent alloys. The
corresponding bulk nanoporous Zn exhibits a hierarchical ligament/pore
architecture characterized by primary ligaments and pores with an
average feature size in the submicrometer range. These primary structures
are made of ultrafine secondary ligaments and pores with a characteristic
feature size in the range of 10–20 nm. Our bulk nanoporous
Zn can split water into H<sub>2</sub> and ZnÂ(OH)<sub>2</sub> at ambient
temperature and pressure and continuously produce H<sub>2</sub> at
a constant rate of 0.08 mL/min per gram of Zn over 8 h. We anticipate
that in this hierarchical bulk architecture, the macropores facilitate
the flow of water in the bulk of the material, while the mesopores
and ultrafine ligaments provide a high surface area for the reaction
of water with Zn. The bulk nanoporous Zn/water system can be used
for on-board or on-demand H<sub>2</sub> applications, during which
H<sub>2</sub> is produced when needed, without prior storage of this
gas compressed in cylinders as it is currently the case
pH-Controlled Dealloying Route to Hierarchical Bulk Nanoporous Zn Derived from Metastable Alloy for Hydrogen Generation by Hydrolysis of Zn in Neutral Water
Dealloyed
nanoporous metals made of very-reactive elements have rarely been
reported. Instead, reactive materials are used as sacrificial components
in dealloying. The high chemical reactivity of nonprecious nanostructured
metals makes them suitable for a broad range of applications such
as splitting water into H<sub>2</sub> gas and metal hydroxide. On
the other hand, the same high chemical reactivity hinders the synthesis
of nanostructured metals. Here we use a pH-controlled dealloying strategy
to fabricate bulk nanoporous Zn with bulk dimensions in the centimeter
range via the selective removal of Al from metastable face-centered
cubic bulk Zn<sub>20</sub>Al<sub>80</sub> at. % parent alloys. The
corresponding bulk nanoporous Zn exhibits a hierarchical ligament/pore
architecture characterized by primary ligaments and pores with an
average feature size in the submicrometer range. These primary structures
are made of ultrafine secondary ligaments and pores with a characteristic
feature size in the range of 10–20 nm. Our bulk nanoporous
Zn can split water into H<sub>2</sub> and ZnÂ(OH)<sub>2</sub> at ambient
temperature and pressure and continuously produce H<sub>2</sub> at
a constant rate of 0.08 mL/min per gram of Zn over 8 h. We anticipate
that in this hierarchical bulk architecture, the macropores facilitate
the flow of water in the bulk of the material, while the mesopores
and ultrafine ligaments provide a high surface area for the reaction
of water with Zn. The bulk nanoporous Zn/water system can be used
for on-board or on-demand H<sub>2</sub> applications, during which
H<sub>2</sub> is produced when needed, without prior storage of this
gas compressed in cylinders as it is currently the case
pH-Controlled Dealloying Route to Hierarchical Bulk Nanoporous Zn Derived from Metastable Alloy for Hydrogen Generation by Hydrolysis of Zn in Neutral Water
Dealloyed
nanoporous metals made of very-reactive elements have rarely been
reported. Instead, reactive materials are used as sacrificial components
in dealloying. The high chemical reactivity of nonprecious nanostructured
metals makes them suitable for a broad range of applications such
as splitting water into H<sub>2</sub> gas and metal hydroxide. On
the other hand, the same high chemical reactivity hinders the synthesis
of nanostructured metals. Here we use a pH-controlled dealloying strategy
to fabricate bulk nanoporous Zn with bulk dimensions in the centimeter
range via the selective removal of Al from metastable face-centered
cubic bulk Zn<sub>20</sub>Al<sub>80</sub> at. % parent alloys. The
corresponding bulk nanoporous Zn exhibits a hierarchical ligament/pore
architecture characterized by primary ligaments and pores with an
average feature size in the submicrometer range. These primary structures
are made of ultrafine secondary ligaments and pores with a characteristic
feature size in the range of 10–20 nm. Our bulk nanoporous
Zn can split water into H<sub>2</sub> and ZnÂ(OH)<sub>2</sub> at ambient
temperature and pressure and continuously produce H<sub>2</sub> at
a constant rate of 0.08 mL/min per gram of Zn over 8 h. We anticipate
that in this hierarchical bulk architecture, the macropores facilitate
the flow of water in the bulk of the material, while the mesopores
and ultrafine ligaments provide a high surface area for the reaction
of water with Zn. The bulk nanoporous Zn/water system can be used
for on-board or on-demand H<sub>2</sub> applications, during which
H<sub>2</sub> is produced when needed, without prior storage of this
gas compressed in cylinders as it is currently the case