Developing of Ethylene Glycol as a New Reducing Agent for

Journal of Petroleum Science and Technology, Vol. 2, No. 2, 2012, 25-32
Developing of Ethylene Glycol as a New Reducing
Agent for Preparation of Pd-Ag/PSS Composite
Membrane for Hydrogen Separation
L. Samiee*, M. Dehghani Mobarake, R. Karami, and M. Ayazi,
Development and Optimization of Energy Technologies Research Division, Research Institute of Petroleum Industry (RIPI)
[email protected]
Abstract
I
n
t
h
e
p
r
e
s
e
nt
wo
r
k,
f
or
t
he
fir
s
t
t
i
me
,
a
pa
l
l
a
di
u
m
s
i
l
v
e
r
me
mbr
a
ne
ha
s
be
e
n pr
e
pa
r
e
d
b
y e
l
e
c
t
r
ol
e
s
s
plating on the surface of a porous stainless steel disk by using ethylene glycol as a new reducing agent
and polyol process. The reducing action of ethylene-glycol in the presence of PVP as a protecting
s
ur
f
a
c
e
a
ge
n
t
pr
o
duc
e
s
a
me
mbr
a
ne
wi
t
h fin
e
l
y
d
i
v
i
de
d powde
r
a
nd
na
n
o
s
i
z
e
d por
e
s
.
Fu
r
t
he
r
mo
r
e
,
t
he
h
ydr
oge
n
s
e
p
a
r
a
t
i
on a
bi
l
i
t
y
of
t
he
me
mbr
a
ne
c
onfir
me
d t
ha
t
t
h
e
me
mbr
a
ne
wi
t
h Pd77Ag23 is highly
selective towards hydrogen compared to other prepared membranes. This is mainly related to the
f
o
r
ma
t
i
on of
d
e
ns
e
a
n
d ho
moge
n
ous
mi
c
r
os
t
r
uc
t
u
r
e
of
t
he
c
oa
t
i
ng.
Mo
r
e
ov
e
r
,
a
c
c
or
di
ng
t
o Gr
a
h
a
m’
s
law, the tests showed that hydrogen purity rises by increasing the applying temperature.
Keywords: Pd-Ag Membrane, Polyol Process, Ethylene Glycol, Hydrogen Separation
Introduction
Attempts to utilize pure palladium as a hydrogen separation membrane were severely hampered by the extremely
high solubility of hydrogen in palladium below 300 °C,
leading to the formation of a separate palladium-hydride
phase, with a much larger lattice constant compared to
pure Pd [1]. The subsequent distortion of the lattice is the
cause of hydrogen embrittlement.
Alloying of palladium with other metals, particularly silver, was investigated by Hunter and coworkers at the Atl
a
nt
i
c
Re
fini
n
g Co
mpa
n
y i
n c
ol
l
a
b
or
a
t
i
on wi
t
h J
.
Bi
s
ho
p Company which later became Johnson-Matthey [2,3]. In
his patent published in 1956 [4], Hunter disclosed that
alloying palladium with 27 wt% Ag not only prevented
hydrogen embrittlement, but also improved the hydrogen permeability of the alloy by 70% compared to pure
palladium at 450 °C.
alkaline electrolysis processes have focused on the use
of advanced anode materials in electrolyzers to reduce
electrode polarization and thereby improving the overall
e
l
e
c
t
r
i
c
a
l
e
f
fic
i
e
nc
y
[
5
]
.
I
t
ha
s
b
e
e
n a
p
pr
e
c
i
a
t
e
d f
o
r
ma
n
y years that electrolytic hydrogen will diffuse through the
walls of the tubular palladium cathode against which it
is generated. This neglected possibility of simultaneous
ge
n
e
r
a
t
i
on a
nd
pur
i
fic
a
t
i
on we
r
e
ut
i
l
i
z
e
d i
n t
he
de
s
i
g
n of some compact electrolytic cells which can yield pure
hydrogen for laboratory or other small scale work. Better
results were obtained with the silver-palladium alloy which
expanded less when fully charged with hydrogen [6-7].
Several methods are available for the formation of hydrogen separation membranes such as phase inversion,
rolling, electroless-plating, chemical vapor deposition
(CVD), sputtering, spray pyrolysis, coatings, metal deposition, sol-gel, and so on [8].
Among other techniques, electroless deposition provides
Historically, the production of high purity hydrogen has
strong advantages such as the uniformity of deposits
been based on the high temperature gas phase hydrogen
even on very complex shapes, very simple equipment,
pe
r
me
a
t
i
o
n,
but
t
h
e
be
n
e
fic
i
a
l
a
s
pe
c
t
s
of
l
ow t
e
mpe
r
a
t
u
r
e
and low cost. This technique can be discussed in three
permeation of high purity hydrogen are very important.
sections; surface activation, bath chemistry, and electroThe electrolysis of aqueous alkaline hydroxide soluless plating procedures [5].
tions has been one of the most popular routes for the
The electroless plating solution generally consists of a
production of hydrogen and oxygen from water. Nometallic salt, a complexing agent, a reducing agent, and
table recent studies concerned with the improvement of
25
Vol. 2, No. 2
Developing of Ethylene Glycol as a New Reducing Agent ... 26
a stabilizing agent. Electroless plating process occurs on
the solid liquid interface between support and the plating
solution. It involves the reduction of a metal salt on a
catalytic surface.
Several reductants are available for the electroless plating process such as dialkylamine-borane, borohydride,
hypophosphite, formaldehyde, and hydrazine. Hypophosphite is commonly used, but deposits contain phosph
or
u
s
,
r
e
d
uc
i
ng t
he
qu
a
l
i
t
y of
t
h
e
fil
m [
5]
.
For
ma
l
d
e

hyde is not a good reducing agent, especially in the case
of Pd deposition since H2 gas is released during plating
and cracks the membrane. Also, the reducing effect of
formaldehyde is very low (Ohno et al., 1985).
Hydrazine is the most commonly used reducing agent. The
disadvantages of hydrazine and related compounds mainly
include toxicity and carcinogenic effects. Hydrazine is toxic
if inhaled, and it is an eye and skin irritant. Besides, the decomposition of hydrazine is directly responsible for the low
p
l
a
t
i
n
g
e
f
ﬁc
i
e
n
c
y
o
f
t
h
e
h
y
d
r
a
z
i
n
e

b
a
s
e
d
p
l
a
t
i
n
g
b
a
t
h
[
5
]
.
Recently, several studies have been reported related to
the fabrication of Pd-Ag alloy particles with uniform microstructure by using ethylene glycol as a solvent and a
reductant agent [9-12].
In the present study, we propose the preparation of PdAg/PSS composite membranes by using electroless deposition and employing ethylene glycol as a reductant
and polyol process.
By considering the ethylene glycol as a reducing agent,
we were therefore stimulated to study the hydrogen separation activity of the new prepared Pd-Ag membrane
and investigate the effect of the ratio of Pd to Ag on the
hydrogen separation activity.
ox
i
di
z
e
d i
n a
hi
gh
t
e
mpe
r
a
t
ur
e
f
ur
n
a
c
e
und
e
r
a
i
r
ﬂo
wi
n
g at 550 °C for 10 hrs.
Table 1: Chemical composition of the alkaline solution
Compound
Amount
Na3PO4.12H2O
45 g
Na2CO3
65 g
NaOH
45 g
DI. Water
1 liter
The rate of heating and cooling during the oxidation
treatment were kept constant at 3 °C.min-1.
Activation Process of PSS Supports
The next step in membrane preparation is the surface activation for seeding the PSS surface with palladium nuclei, which helps to achieve a better autocatalytic process
of reduction of a metastable metal salt complex on the
target surface during electroless plating. Solutions for
the activation were prepared using tin (II) chloride dihydrate and palladium (II) chloride. Two solutions were
prepared by dissolving 1 g.l-1 SnCl2 and 0.1 g.l-1 PdCL2
salts in 1 ml.l-1 of HCl solution. The activation process
consisted of the immersion of the supports in an acidic
SnCl2 solution (sensitizing) followed by an acidic PdCl2
solution at room temperature. After the immersion in the
SnCl2 solution, a gentle rinsing with deionized water was
used. Finally, the samples were rinsed with 0.01 M HCl
and then with water. This cycle was repeated normally
six to nine times.
Electroless Plating of Pd and Ag
A typical experimental procedure for electroless plating
is described as follows:
First, 0.1331 gr of PdCl2 and 0.7980 gr of PVP were disExperimental Procedures
solved in 15 ml of ethylene glycol as a solvent, and the
Membrane Supports
formed suspension was mechanically stirred for 10 min
Por
o
us
316
L s
t
a
i
n
l
e
s
s
s
t
e
e
l
(
PSS)
s
up
por
t
s
(
0
.
2 μm to allow the dissolution of the precursors. Then, 0.1274
grade) were purchased from Mott Metallurgical Corpogr of AgNO3 and 0.8090 gr of PVP were added to the
ration. PSS plates were prepared by cutting 1 dm2 PSSabove suspension under agitation for 1 hour. The total
316L sheets into 53.066 cm2 circular pieces.
concentration of metal ions and the ratio of PVP to the
metal were kept at 0.05 M and 10 (w/w) respectively.
Cleaning of the Supports
The surface of the PSS supports was cleaned prior to
electroless deposition to remove contaminants such as
oil, grease, and dirt.
The plating was done at 120 °C after 5 hours. Finally, the
samples were rinsed in hot water and dried at 120 °C for
3 hours. The membranes were prepared for the different
ratios of Pd to Ag.
The composition of the alkaline solution used is given in
Table 1. Then, the samples were thoroughly washed with
high purity water (DI water) to remove the basic solution
trapped in the pores of the supports. The last cleaning
step involved a 10 min immersion in iso-propanol to easily remove the water inside the pores. All cleaning steps
were carried out in ultrasonic bath at 60 °C. Finally, the
supports were dried at 120 °C for 3 hrs.
The
t
he
r
ma
l
t
r
e
a
t
me
nt
o
f
a
s

d
e
pos
i
t
e
d
Pd–Ag
ﬁl
ms
wa
s
carried out in a high temperature furnace under an N2
atmosphere. The temperature was increased at a rate
of 1 °C.min-1 until it reached 550 °C and then was kept
constant at this temperature for 10 hrs. After cooling the
samples, they were put in a reactor and their permeation
tests were carried out.
Formation of an Oxide Barrier Layer
After cleaning, the porous stainless steel supports were
Membrane Characterization
Surface characterization was performed using a Philips
XL30, 17 kV equipped with an EDX light element detec
27 Samiee et al.
Journal of Petroleum Science and Technology
tor. The X-ray diffraction (XRD) patterns of all the sampl
e
s
we
r
e
c
ol
l
e
c
t
e
d i
n a
2θ
r
a
n
ge
be
t
we
e
n 3
0 °
a
nd
60
°
by
us
i
ng
Phi
l
i
p
s
PW184
0 di
f
f
r
a
c
t
ome
t
e
r
(
Cu Kα1 r
a
di
a

t
i
on,
Kα1 = 1.
54
06Å)
Mi
c
r
o
g
a
s
c
h
r
oma
t
og
r
a
ph
y(
mode
l
Agilent 3000A) was used to analyze the outlet gases of
the membrane.
pe
a
k
s
a
t
2θ
=39
.
92
°
a
n
d 2
θ
=46.
29°
a
r
e
r
e
l
a
t
e
d t
o Pd

Ag alloy phase corresponding to 111 and 200 respectively.
These results strongly indicate that the membrane obtained is an alloy of Pd and Ag [13]. The average particle
size of the Pd-Ag alloy nanoparticles (d) was estimated
by using Scherrer equation after background subtract
i
on f
r
o
m (
1
1
1)
pe
a
k a
t
2
θ
=39
.
42°
.
I
n t
he
be
s
t
s
a
mpl
e
Single Gas Permeation Test of the Membranes
(Pd77Ag23), the average particle size of the nanoparticles
was around 11 nm. Figure 3 shows the typical scanning
A shell-and-tube apparatus shown in Figure 1 has been
electron micrograph of the PSS coupons that were plated
e
qu
i
ppe
d
wi
t
h ma
s
s
ﬂow c
ont
r
ol
l
e
r
s
,
p
r
e
s
s
ur
e
c
on
t
r
ol
with Pd-Ag intermetallic alloy.
valves, and a temperature indicator to measure the permeation of hydrogen and nitrogen through the present
In the present work, the polyol process has been used for
membranes. Both ends of the membrane tube were concoating the PSS membrane. The polyol process has been
nected to inlet and outlet tubes and placed in the center of
r
e
c
e
n
t
l
y
p
r
op
os
e
d
a
s
a
me
t
h
od f
o
r
t
h
e
p
r
e
pa
r
a
t
i
o
n of
ﬁn
e

furnace. Hydrogen and nitrogen gases with a ratio of 50
ly divided powders of easily reducible metals [10,11]. A
to 50 were introduced into the membrane tube from outer
suitable solid inorganic compound is dissolved or suss
he
l
l
t
hr
o
ugh
t
he
ma
s
s
flo
w c
ont
r
o
l
l
e
r
a
nd t
h
e
ga
s
pe
r
me
pended into a liquid polyol (e.g., ethylene-glycol, diethated through the membrane. Online gas chromatography
ylene-glycol or a mixture of both). Afterward, the system
was used to analyze the outlet gas of the membrane; it
is stirred and heated to a given temperature, which can
should be noted that the calibration of the chromatograreach the boiling point of the polyol for less easily rephy was already performed with hydrogen gas (99.999%
ducible metals. The reduction of the starting compound
purity).
yi
e
l
ds
t
h
e
me
t
a
l
a
s
a
fin
e
l
y
d
i
vi
de
d po
wde
r
.
The
s
t
a
r
t
i
n
g compound may be a hydroxide, an oxide or a convenient
A single point calibration was done by using the micro
salt. The main feature of the reaction mechanism is that
TCD’
s
l
i
ne
a
r
d
yna
mi
c
r
a
n
ge
of
10 pp
m t
o
1
00 pe
r
c
e
nt
.
the reduction reaction proceeds via the solution rather
The system has a repeatability of 0.5 percent relative
than the solid phase. Therefore, the metal particles are
standard deviation and a linear detector response of
formed by nucleation and growth from solution. Accord±5
pe
r
c
e
n
t
o
ve
r
five
o
r
de
r
s
of
ma
gn
i
t
u
de
.
I
n
f
or
ma
t
i
o
n ing to this mechanism, the polyol acts as a solvent for
is displayed in up to six display windows that support
the starting inorganic compound due to the rather high
r
e
a
l

t
i
me
mo
ni
t
or
i
ng
o
f
t
he
de
fine
d s
i
gna
l
s
o
f
ni
t
r
og
e
n dielectric constant of these organic media. In particuand hydrogen compounds. Data is also sent to a CSV
lar, silver nitrate and palladium chloride are soluble in
fil
e
f
or
l
a
t
e
r
p
r
oc
e
s
s
i
ng
i
n Mi
c
r
os
of
t
Ex
c
e
l
,
f
o
r
e
xa
mpl
e
.
ethylene-glycol to such an extent that a complete dissoThe
me
a
s
ur
e
me
n
t
s
of
hyd
r
og
e
n a
n
d ni
t
r
oge
n
p
ur
i
fic
a
t
i
o
n l
ut
i
on
i
s
ob
s
e
r
v
e
d a
s
t
he
fir
s
t
s
t
e
p of
t
he
r
e
a
c
t
i
o
n.
Nuc
l
e

level were made at different temperatures (25-120 °C)
ation and growth must be completely separated in order
and at a pressure difference of 400 kPa.
to explain the fact that the obtained metal suspension is
a
n a
l
mos
t
ho
mod
i
s
pe
r
s
e
s
y
s
t
e
m.
Thi
s
c
ond
i
t
i
o
n,
ﬁr
s
t
e
x

Results and Discussion
pressed by La Mer [12, 13] in his study about sulfur sols
Structural Study of Pd/Ag Membrane
f
r
o
m a
c
i
di
fie
d t
hi
os
ul
f
a
t
e
s
ol
ut
i
o
n,
a
pp
e
a
r
s
a
s
a
g
e
ne
r
a
l
The phase properties of the Pd-Ag alloy membrane were
condition to obtain a homodisperse system. The metal is
investigated using XRD measurements. The results from
slowly provided in solution by the progressive reduction
XRD analysis are shown in Figure 2. The diffraction
of the dissolved species.
Figure 1: Schematic presentation of gas permeation apparatus
Developing of Ethylene Glycol as a New Reducing Agent ... 28
Vol. 2, No. 2
2
θ
(
°)
Figure 2: XRD pattern of Pd-Ag alloy
A
B
D
C
E
Figure 3: Sc
a
n
ni
n
g e
l
e
c
t
r
on
mi
c
r
o
gr
a
ph
s
o
f
o
xi
d
i
z
e
d
PSS a
f
t
e
r
p
l
a
t
i
ng
a
t
di
f
f
e
r
e
n
t
Pd t
o
Ag r
a
t
i
os
;
a
:
50
:
5
0
,
b
:
60
:
40
,
c
:
7
7:
23
,
d:
8
8:
1
2,
e
:
9
8:
2
29 Samiee et al.
Journal of Petroleum Science and Technology
In particular, the reducing action of ethylene-glycol can
be monitored by analyzing the volatile compounds resulting from its oxidation. The formation of the main
product, i.e. diacetyl, can be explained in terms of a
double oxidation of acetaldehyde, previously produced
by the dehydration of ethylene-glycol [11], as follows:
CH2OH-CH2OH H O CH3-CHO
(1)
2CH3CHO
M+2H++CH3-CO-CO- CH3
(2)
2
During reaction (2), the metal concentration rises to the
saturation where the nucleation can occur.
This condition results in the formation of many nuclei in
a short burst. They grow rapidly and the metal concentration is lowered to a point below the nucleation concentration, but high enough to allow particle growth to occur
at a rate that just consumes all the generated metal. An
envelopment of the reduced metal atoms within a suitable layer could act as a protection for the nanometric
particles during their growth [14, 17]. A number of organic materials are known to work as protective agents
for preventing colloid sintering [18]. Among them, poly
(N-vinylpyrrolidone) (PVP) exhibits the best protecting
properties. The prevention of particle sintering can be
achieved by adding a critical dosage of an organic protective agent which covers the particles and inhibits any
possibility of metal-metal particle bond formation.
Such coordination interaction and the repulsion between
polymer chains of PVP make the adsorption of PVP to be
or
i
e
n
t
e
d i
n s
ome
de
fini
t
e
di
r
e
c
t
i
ons
,
whi
c
h
l
e
a
ds
t
o
t
he
growth of particles occurring in the preferred directions
and being inhibited in other directions. This factor also
c
on
t
r
i
but
e
s
t
o
pa
r
t
i
c
l
e
s
h
a
pe
a
nd
t
h
e
fin
a
l
s
ha
p
e
d
i
s
t
r
i
bu

tion. An increase in the concentration of the protecting
agents suppresses the growth of metal particles, leading
to smaller metal nanoparticles [12, 23].
Because of the relatively high temperature used in the
annealing process, wide Brownian motions characterize
the particles, and the atoms on their surface have an elevated mobility. Consequently, the probability of particle
collision, adhesion, and subsequent coalescence by sintering is enhanced.
Figure 3 shows that the deposits are a mixture of individual particles. EDS analysis (Figure 4) also proves that
these particles are composed of Pd and Ag metals. With
a further annealing step, these deposits make the Pd-Ag
alloy.
Moreover, it can be clearly seen that a change in the
me
t
a
l
r
a
t
i
o i
n t
he
ba
t
h ha
s
a
s
i
gn
i
ﬁc
a
n
t
e
f
f
e
c
t
on
t
h
e
d
e

posit concentration; an increase in the concentration of
Ag in the solution results in an increase in the deposit
concentration. Due to the very thin layers of Pd and Ag,
the pores of the substrate can clearly be seen in Figure
3.e. As can be inferred from Figure 3, Ag shows a preferential deposition onto Pd. The deposits obtained are
bimetallic; therefore, an increase in the Ag concentration
in the deposits means relatively more surface coverage
by Ag deposits than Pd deposits. The lower catalytic
activity of Ag for the ethylene glycol oxidation means
that as the Ag concentration in the deposits increases, the
electroless deposition potential rises too. The high overpotential associated with the Pd deposition also means
that when the Ag concentration is 2 wt% in the solution,
the electroless deposition potential decreases to an extent
that the Pd deposition is not possible anymore [24].
Ag has a passivating effect on the Pd deposition. The
Ag passivating effect was explained on the basis of the
electrode potential of the metal ions in the bath. Figure 3
shows that the electrode potential of the Ag ions is less
than that of Pd up to 23 wt% of Ag and the sample containing 77 wt% of Pd and 23 wt% of Ag (Pd77Ag23) has
a
u
ni
f
or
m s
ha
pe
d
mi
c
r
os
t
r
uc
t
u
r
e
;
ho
we
v
e
r
,
a
f
t
e
r
2
wt
% Ag in the bath, covering tendency is coming down. The
worst condition can be easily seen in the sample containing 98 wt% of Pd and 2 wt% of Ag (Pd98Ag2).
Table 2: Comparison between the initial ratio of Pd to Ag and the
obtained ratio of Pd to Ag by EDS
Initial Ratio of Pd to Ag
Obtained Ratio of Pd to Ag by EDS
50:50
46:54
60:40
62.7:37.3
77:23
76.3:23.7
88:12
88.5:11.5
98:2
96:4
Hydrogen Permeation Behavior of the Membrane
With respect to using the prepared membrane as a hydrogen diffusion cathode in electrolyzing systems, the membranes were tested for H2 and N2 permeation at the range
of 25-120 °C. Table 3 shows the hydrogen and nitrogen
purities after passing through the membrane at the applied temperatures. As can be seen in Table 3, the hydrogen passed through the Pd77Ag23 membrane , which has
a homogenous and dense alloyed layer, has a maximum
purity, whereas the hydrogen passed through the Pd98Ag2
membrane (with the least coating has less purity. This
problem can be possibly due to the formation of a nonhomogeneous alloy with layers that contained higher Pd
content than the desired composition. Also, the characterization of this membrane shows that the maximum H 2
purity can be achieved for the membrane with reduced
support porosity.
(3)
diffusion
In addition, since a constant volume of different gases
contains the same number of particles, the number of
moles per liter at a given temperature (T) and pressure
(P) is constant. Therefore, the density of a gas is directly
proportional to its molar mass (MM):
(4)
Thus, it can be concluded that H2 diffuses more rapidly
than N2 by increasing temperature [25].
Vol. 2, No. 2
Developing of Ethylene Glycol as a New Reducing Agent ... 30
Figure 4: EDS An
a
l
ys
i
s
o
f
o
x
i
d
i
z
e
d
PSS a
f
t
e
r
p
l
a
t
i
ng
a
t
di
f
f
e
r
e
n
t
Pd t
o
Ag r
a
t
i
o
s
;
a
:
50
:
5
0
,
b
:
6
0:
40
,
c
:
7
7:
23
,
d:
8
8
:
1
2,
e
:
9
8
:
2
31 Samiee et al.
Journal of Petroleum Science and Technology
Table 3: Hydrogen purity (%)
Applied temperature (ºC)
Hy
dr
o
ge
n pu
r
i
fic
a
t
i
o
n (
%)
t
hr
o
ug
h
me
mbr
a
ne
wi
t
h
d
i
f
f
e
r
e
n
t
Pd t
o
Ag r
a
t
i
o
s
98:2
88:12
77:23
60:40
51:49
25
87.3571
92.1472
99.9847
93.8153
90.3591
40
87.8462
93.4253
99.9891
94.2684
91.1473
60
88.4392
94.0026
99.9903
95.1275
92.8735
80
89.0173
94.8472
99.9918
96.0073
95.4263
100
89.8637
95.7361
99.9924
96.8165
95.8462
120
90.2755
96.0752
99.9936
97.5739
96.2639
The comparison results between the initial ratio of Pd
to Ag and the obtained ratio of Pd to Ag by EDS also
c
on
fir
ms
t
h
e
r
e
l
i
a
bi
l
i
t
y of
t
hi
s
r
e
duc
i
n
g a
g
e
nt
(
Ta
bl
e
2
)
.
Conclusion
A palladium-silver membrane was developed by depositing Pd-Ag onto a PSS substrate by a polyol process. A
s
moot
h
,
fla
t
,
a
nd de
n
s
e
Pd
Ag l
a
ye
r
i
s
o
bt
a
i
ne
d a
t
f
or
a
combination of 77 wt% Pd and 23 wt% Ag (Pd77Ag23).
Due to the passivating effect the porous structure increases remarkably as the ratio of Pd to Ag is increased,
Hydrogen purity measurements in the temperature range
of 25 to 120 °C shows that the composite membrane has
a high selectivity for hydrogen. The permeation tests
shows that hydrogen purity level rises by increasing
temperature, which represents a good reliability of the
prepared membrane for using as a hydrogen diffusion
cathode in the operating temperature range of electrolyzer systems.
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