8.1 The Dynamic Bubble Template Method
265
was much smaller than the bubble lifetime [12]. The reverse pulse method resulted in
a non-monotonous dependence of the primary pore size on the reverse pulse current
density, exhibiting a minimum pore size at an intermediate current density of the
anodic pulse [13]. These results, especially the pore size variation during the reverse
pulse method, have not been completely elucidated.
8.1.3 Miscellaneous Other Materials and Methods Related
to the Dynamic Bubble Template Approach
Although water is the typical medium for the DHBT method, the variety of the
solvents can be extended to non-aqueous molecular liquids in which the hydrogen
evolution takes place at very negative potentials, hence allowing the deposition of
metals whose deposition is not accessible in aqueous systems. It has been demonstrated [50] that Fe–Ce intermetallic compounds with porous structure can be
deposited from a dimethyl sulphoxide–urea plating bath with potential scans ranging
to the hydrogen evolution regime (−2.8 V vs. SCE).
An interesting as well as economic method was shown for the application of
DHBT-plated non-noble metal foams to transform them into noble metal-coated
porous structures [51–53]. In the first step of the process, an inexpensive non-noble
metal foam was prepared with the standard DHBT method, and then it was exposed
to a solution containing a noble metal salt of small concentration. The displacement
of the LN metal at its rest potential (i.e., without any electrochemical control) led
to a conformally coated foam with the displacing noble metal. With this technique,
the pore structure can be shaped with an inexpensive metal (e.g., Cu), and pore sizes
occasionally not available with a direct deposition of Pd or Ag can be achieved. The
unused portion of the expensive noble metal salt can be simply washed out from the
porous structure after the completion of the displacement reaction. The average noble
metal content of the displacement-modified porous structure was shown to be only
about 2 at.% [52], which makes it possible to drive the process efficiently, achieving
a high-surface-area noble metal coating on an inexpensive dendritic porous scaffold.
The feasibility of a second electrodeposition step producing a coating on the
already formed porous metals was also realized for Ni [54] and Cu [23] deposition
onto porous Cu. The composition of the second plating bath was similar to those
applied in the deposition of conventional coatings, not to those applied for the DHBT
method. Surprisingly, the deposition of the additional layer led to a conformal coating,
which means that the deep layers of the pore system were coated similarly as the top of
the sample. Therefore, no significant electric field effect was experienced that would
be expected to result in a preferential deposition on the top of the samples. However,
the second electrodeposition step leads to the disappearance of the secondary porosity
of the samples.
265
was much smaller than the bubble lifetime [12]. The reverse pulse method resulted in
a non-monotonous dependence of the primary pore size on the reverse pulse current
density, exhibiting a minimum pore size at an intermediate current density of the
anodic pulse [13]. These results, especially the pore size variation during the reverse
pulse method, have not been completely elucidated.
8.1.3 Miscellaneous Other Materials and Methods Related
to the Dynamic Bubble Template Approach
Although water is the typical medium for the DHBT method, the variety of the
solvents can be extended to non-aqueous molecular liquids in which the hydrogen
evolution takes place at very negative potentials, hence allowing the deposition of
metals whose deposition is not accessible in aqueous systems. It has been demonstrated [50] that Fe–Ce intermetallic compounds with porous structure can be
deposited from a dimethyl sulphoxide–urea plating bath with potential scans ranging
to the hydrogen evolution regime (−2.8 V vs. SCE).
An interesting as well as economic method was shown for the application of
DHBT-plated non-noble metal foams to transform them into noble metal-coated
porous structures [51–53]. In the first step of the process, an inexpensive non-noble
metal foam was prepared with the standard DHBT method, and then it was exposed
to a solution containing a noble metal salt of small concentration. The displacement
of the LN metal at its rest potential (i.e., without any electrochemical control) led
to a conformally coated foam with the displacing noble metal. With this technique,
the pore structure can be shaped with an inexpensive metal (e.g., Cu), and pore sizes
occasionally not available with a direct deposition of Pd or Ag can be achieved. The
unused portion of the expensive noble metal salt can be simply washed out from the
porous structure after the completion of the displacement reaction. The average noble
metal content of the displacement-modified porous structure was shown to be only
about 2 at.% [52], which makes it possible to drive the process efficiently, achieving
a high-surface-area noble metal coating on an inexpensive dendritic porous scaffold.
The feasibility of a second electrodeposition step producing a coating on the
already formed porous metals was also realized for Ni [54] and Cu [23] deposition
onto porous Cu. The composition of the second plating bath was similar to those
applied in the deposition of conventional coatings, not to those applied for the DHBT
method. Surprisingly, the deposition of the additional layer led to a conformal coating,
which means that the deep layers of the pore system were coated similarly as the top of
the sample. Therefore, no significant electric field effect was experienced that would
be expected to result in a preferential deposition on the top of the samples. However,
the second electrodeposition step leads to the disappearance of the secondary porosity
of the samples.