The formation of palladium nanocomposite catalysts on the porous silicon used as anodes of fuel cells

Article abstract of DOI:10.1007/s11172-010-0267-0

Palladium nanoparticles on the porous silicon were synthesized by radiation-chemical reduction in the solution of reversed micelles. The Pd nanoparticles obtained are electron deficient. The porosity, the type of conductivity, the silicon matrix pore geom

Full text of DOI:10.1007/s11172-010-0267-0

1482
Russian Chemical Bulletin, International Edition, Vol. 59, No. 8, pp. 1482—1487, August, 2010
The formation of palladium nanocomposite catalysts
on the porous silicon used as anodes of fuel cells
N. A. Yashtulov,a S. S. Gavrin, A. A. Revina, and V. R. Flid
a
b
a
aM. V. Lomonosov Moscow State Academy of Fine Chemical Technology,
6 prosp. Vernadskogo, 119571 Moscow, Russian Federation.
8
Fax: +7 (495) 434 7111. Eꢀmail: YashtulovNA@rambler.ru
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
b
3
1 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 955 4017
Palladium nanoparticles on the porous silicon were synthesized by radiationꢀchemical
reduction in the solution of reversed micelles. The Pd nanoparticles obtained are electron
deficient. The porosity, the type of conductivity, the silicon matrix pore geometry, and precurꢀ
sor parameters influence the size, the shape and the charge state of palladium catalysts. The
δ+
mechanism of Н and HCOOH electrooxidation on porous silica in the presence of Pd /Pd
2
redox pair is proposed.
Key words: palladium nanocomposites, porous silicon, atomic force microscopy, specific
adsorption, electrocatalysis.
The unique properties of the porous silicon (PS) offer
the possibility for developing electrocatalytic composites
increase the efficiency of FC operation the development
of catalytically active electrodes reactions on anode and
cathode is needed.
2
–1
with high surface area (more than 400 m g ) and for
preparing specific catalysts in the structure directing
porous matrix with the desirable size and shape.1 The
lowꢀpower electric sources of the new generation for elecꢀ
tronics compatible with the silicon microchips are conꢀ
structed on the base of catalytically active PS composꢀ
ites.5 The use of catalysts in the form of nanoꢀsized
particles increase their efficiency and decrease their
consumption, that is especially important in case of the
metals of platinum group. Previously7 we described the
results of the synthesis and the application of the pallaꢀ
dium, silver and platinum nanocomposite catalysts for
the hydrogenꢀair fuel cells (FC).
In the development of the novel catalytic systems for
the lowꢀtemperature FC anodes the use of Pd and its
—4
2
,9
composites is at present the most promising option.
The Pd composites possess high catalytic activity in
the reactions of oxidation of the widespread fuel types
(hydrogen, formic acid, ethanol, etc.) and they are stable
,6
9
toward СО, which is a common catalyst poison in FCs.
The aim of the present work is the study of influence
of conductivity type, porosity, silicon pore geometry and
precursor parameters on surface potential, adsorption
capacity, charge state, as well as catalytic activity of the
synthesized Pd nanoparticles. The search of correlations
between the parameters of adsorption composites and their
catalytic activity helps one to find the features of the
electrochemical reaction mechanisms involving nanoꢀ
composite catalysts.
,8
The development of FC is considered as one of the
main breakthrough technologies in the energetics of
the 21st century. The efficiency of the direct transformaꢀ
tion of the chemical energy to the electric energy in the
cells achieves 50—70%. The fuel in the PSꢀbased FC is
hydrogen, methanol, ethanol or formic acid, whereas the
oxidant is the oxygen of the air. The reaction products are
either H O or H O with СО . In the internal circuit, the
Experimental
2
2
2
The surface potential of PS samples was measured using a
NTegra Prima (NTꢀMDT) atomicꢀforce microscope by probe
ionic electrolyteꢀconductor should provide migration of
ions and separation of the fuelꢀreductant and the oxidant.
In the modern lowꢀtemperature FCs the proton exchange
membranes are usually utilized as electrolytes. These
membranes <0.2 mm thick are prepared from perfluorꢀ
inated ionꢀexchange polymer permeable to protons. To
10
method of Kelvin. The method of double pass was used: the
pattern was determined during the first pass over the studied
surface, the electric interaction of the probe with the sample at a
fixed distance between the probe and the sample (10 nm) was
measured during the second pass. The frequency signal detection
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1450—1455, August, 2010.
066ꢀ5285/10/5908ꢀ1482 © 2010 Springer Science+Business Media, Inc.
1

Palladium nanocomposite catalysts on silicon
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1483
allowed the surface potential distribution (U ) to be traced. The
U /V
s
s
values of U for PS at different solubilization extent (ω ) of
s
0
palladium solutions were determined on the first stage, the
1.0
dependencies of U of silicon on its porosity at the fixed value of
ω0 of Pd solutions were found on the second stage.
3
s
0
0
0
.8
4
1
The Pd nanoparticles were synthesized in accordance with
the previously described procedure by radiationꢀchemical
.6
.4
2
+
reduction of Pd ions in anaerobic conditions in reversed
micelles solutions with the subsequent adsorption of nanoꢀ
2
1
1,12
particles on the surface of PS.
The reversed micelles are the
0.2
0
micro drops of aqueous solution (pools) stabilized with the
surfactant in isooctane. Sodium bis(2ꢀethylhexyl)sulfosuccinate
(
АОТ) (С H SO Na, 99%, Sigma) was used as a surfactant.
20 37 7
–
0.2
The solution of 0.02 М [Pd(NH ) ]Cl complex (chemically
3
4
2
pure) was used in the synthesis. The prepared solutions were
6
0
sealed and then exposed to γꢀirradiation Co using a PCMꢀγꢀ20
2
0
40
60
80
P (%)
setup. The molar water to АОТ ratio was varied from 1.5 to 5, that
corresponded to the solubilization extent ω = [H O]/[AOT] =
Fig. 1. The dependencies of surface potential of PS (U ) on the
porosity (P) at solubilization extent ω = 5 for the samples of PS
s
0
2
=
1.5—5. The total Pd content in the studied solutions is
0
of nꢀtype (1) and pꢀtype (2) and for palladium nanocomposites
with PS of nꢀtype (3) and pꢀtype (4).
determined by the value ω ; for the values ω = 1.5, 3 and 5 the Pd
concentrations were 8.1•10 , 1.62•10 and 2.7•10 mol L
0
0
–5
–4
–4
–1
respectively. The size and the composition of the nanoparticles
formed can be controlled by varying the conditions of synꢀ
Table 1. The dependencies of the surface potential
of Pd nanocomposites on PS on the porosity level
2
,12
thesis.
The content of Pd nanoparticles on the surface was
varied from 2 to 10 weight % assuming their adsorption in the PS
nanopores the surface concentration of Pt lies in the range
(
P) of silicon and the type of conductivity at ω = 5
0
6
—23 weight %.
The samples of PS nꢀ and pꢀtype conductivity with the
P
Conductivity
U (PS)
U (Pd + PS)
s
s
(
%)
different porosity (P) (40—78%) were obtained according to
the previously described procedures.
V
7
,8
The PS plates were
subjected to anode electrochemical etching in waterꢀethanol
solution of HF. During the galvanostatic mode of anodizing the
current density was within 20—100 mA cm . The resulted width
of porous layer was 1 μm, the diameter of pore channels for the
PS of nꢀtype was within 20—50 nm, whereas for pꢀtype it was
0
0
n
p
n
p
n
p
n
p
0.60
0.28
0.32
0.03
0.34
0.05
0.99
0.70
0.11
–0.06
0.08
–0.08
–0.07
–0.26
–
2
40
51
61
64
78
76
5
—20 nm.
The Xꢀray photoelectronic spectra of the Pd nanoparticles
0.40
–0.03
adsorbed on PS were registered using a Perkin—Elmer PHI 5500
ESCA spectrometer. The monochromatic AlꢀKαꢀemission
(
hν = 1253.6 eV) was used for the activation of photoemission.
0
.99 V) and pꢀtype (from 0.28 to 0.7 V) conductivities.
The spectra with high resolution were obtained with the
transmission energy of analyzer equal 29.35 eV and the frequency
of data collection equal 0.125 eV per step. The diameter of the
analyzed area was 1.1 mm.
However in the case of adsorption of Pd nanoparticles on
the PS an unusual reversed effect is observed. The effect is
that not only the values U for the Pdꢀcontaining comꢀ
s
The measurements of the adsorption spectra within interval
of wavelengths 190—1000 nm were performed using a Shimadzu
UVꢀ3101 PC spectrometer at room temperature. The reference
solution was 0.15 М solution АОТ—isooctane.
posites are lower than for nonꢀporous silicon, but they are
also lower than those for PS of any porosity that does not
contain Pd. For the Pd nanocomposites with PS of elecꢀ
tronic nꢀtype conductivity U have approximately the same
s
values as for PS of the hole pꢀtype conductivity in the
absence of Pd at the porosity range within 40—80%.
When the porosity level of pure PS without Pd inꢀ
creases from 40 to 80% the surface potential changes negꢀ
ligibly for silicones of nꢀtype (0.32—0.40 V) and of pꢀtype
(from 0.03 to –0.03 V). At the same time, similar to Pd
Results and Discussion
The dependencies of the surface potential of PS and
Pd nanocomposites with PS at ω = 5 for nꢀ and pꢀtype of
0
conductivity on the porosity (P) of silicon matrix are
shown in Fig. 1 and in Table 1. The modification of the
plain nonꢀporous (P = 0%) silicon with the Pd nanoꢀ
nanocomposites, the decrease of U is observed, espeꢀ
s
cially at a porosity level of ~80%. The difference between
particles results in the U increase, that suggests the
values of U for the nanocomposites of nꢀ and pꢀtype of
s
s
increase in the electronic type conductivity. The pattern
PS is approximately the same (from 0.16 to 0.19 V) for all
of increasing values of U is similar for nꢀtype (form 0.6 to
samples with P > 40%. It can be thus inferred, that on
s

1484
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
Yashtulov et al.
preparing the active Pdꢀbased electrodes the contribution
of both the porosity and the type of conductivity of PS
I (rel. units)
a
matrix into the summary value of U should be taken into
1
8
6
4
2
s
consideration. The different behaviour of Pd nanoparticles
on the samples of plain and porous silicon, as well as the
2
3
difference of the U values of PS in the absence and in
s
the presence of Pd suggest, that the absorption processes
and the charge states of Pd nanoparticles on PS and on
the nonꢀporous silicon are different.
The data concerning the influence of the solubilizaꢀ
tion extent on the changes of the U values of Pd nanoꢀ
s
composites on PS of nꢀ and pꢀtype are listed in Table 2.
3
44
340
336
Eb/eV
The value ω determines size distribution of Pd nanoꢀ
0
particles in the aqueous pool of the reversed micelles and
considerably influences the subsequent formation of
nanocomposites in the course of adsorption. It follows
I (rel. units)
from the Table 2, as of the ω value increases the surface
1
b
10
8
0
potential decreases for nanocomposites with any type of
conductivity. The decrease in U caused by the increase of
s
2
ω from 1.5 to 5 for nꢀtype (0.15 V) is nearly the same as
0
6
that observed for the pꢀtype (0.11 V). The highest Us
change is observed in the solutions with с ω = 5, for
0
4
which the maximum sizes of the aqueous pool of micelles
and an increased content of the smallꢀsize fraction of Pd
nanoparticles are typical.2
3
2
,3
For the estimation of the charge state and the concenꢀ
tration of the Pd nanocomposites on the PS surface the
samples of nꢀ and pꢀtypes of conductivity were studied by
Xꢀray photoelectron spectroscopy (XPS) at the fixed value
3
44
340
336
E /eV
b
Fig. 2. The XPS spectra of Pd (3d3/2 and 3d5/2) of Pd nanoꢀ
composites with PS of nꢀtype (a) and pꢀtype (b) of conductivity:
1 — general view, 2 — Pd , 3 — Pd .
0
2+
of the porosity and ω = 5. The fragments of high resoluꢀ
0
tion spectra of Pd(3d) with nonꢀlinear approximation are
shown in Fig. 2. The Pd(3d) spectra consist of duplet 3d5/2
and 3d3/2, caused by spinꢀorbit splitting. In the spectra
of the studied samples each of duplet contains two
components, corresponding to the two differently charged
Table 3. The characteristics of XPS spectra of Pd nanocomposites
on PS with nꢀtype and pꢀtype conductivity
Type of
Eb(3d5/2)/eV
The content of Pd (wt.%)
0
2+
components of Pd: neutral Pd and ionic Pd (see Table 3).
In accordance with the reference data13 the bond energy
conductivity
Pd0
Pdδ+
Pd0 + Pdδ+ Pdδ+/(Pd0 + Pdδ+)
(
P (%))
Е (3d5/2) in Pd metal is 335.1±0.2 eV, whereas for doubly
b
charged ion it is Е (3d5/2) = 336.5±0.2 eV. With allowꢀ
b
n (40)
p (51)
335.1
335.1
336.8
336.6
1.6—1.9
6.5—10.3
40
30
ance for the experimental error these values correspond
to the peak positions observed for our samples. According
2
+
to XPS data the contribution of ionic Pd state is fairly
high and in the samples with PS of nꢀtype it is higher than
in case of pꢀtype of surface.
Earlier11 we analyzed the micro diffraction pictures of
the nanoꢀsized Pd particles obtained from the solutions of
reversed micelles on the ceramic supports (in particular,
silica gel KSKꢀ2) without nanopores. It was shown,1 that
the Pd nanoparticles formed had faceꢀcentered cubic latꢀ
tice with the space group Fm3m, corresponding to the Pd
metal. According to the data of atomic force microscopy
1
Table 2. The dependence of the surface potential
(
U ) of Pd nanocomposites Pd on PS on solubilizaꢀ
s
tion extent
4
,7
(
AFM) the nanoparticles of Pd metal were also observed
The type of
conductivity
U /V
s
on the surface of non porous silica (P = 0%). Therefore,
to discuss the catalytic processes on the PS surface one
should take into account the contribution of ionic state of
palladium nanoparticles Pd , which, probably, can arise
as a result of electron density transfer onto the electron
ω0 = 1.5 ω0 = 3 ω0 = 5
n (40)
p (51)
0.26
0.05
0.15
–0.04
0.11
–0.06
δ+

Palladium nanocomposite catalysts on silicon
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1485
deficient PS matrix. The transfer of electronic density
from the catalyst onto matrixꢀcarrier was observed earꢀ
Table 4. The change of the total integral intensity of
the absorption of the Pd solutions resulted from the
adsorption on PS
9
,14,15,16
lier
for the range of the systems, where the catalyst
was in a bulk rather than in the nanoꢀsized state.
Type of
conductivity
The change of the intensity (%)
ω0 = 1.5 ω0 = 3 ω0
The values of the surface potential obtained by AFM,
and data on the charge state and the content of nanoꢀ
particles obtained by XPS, provide description of the near
surface (often monomolecular) layer and not the bulk
sample. The Кαꢀirradiation from Mg and Al used in the
present work give the possibility of the collecting the data
from the near surface layer with the depth of 2—3 nm or less.
According to the data of XPS the concentrations Pd
on the PS surface of nꢀtype and pꢀtype the conductivities
are different. The content of the particles adsorbed to the
surface of PS of pꢀtype is 3—6 times that of the nꢀtype
=
5
(
P (%))
n (40)
p (51)
22.7
10.8
12.7
6.5
19.0
10.9
listed in Table 4. Later on the integral intensity changed
insufficiently. The integral intensity is proportional to the
number of nanoparticles in the sample and can be a meaꢀ
sure of the concentration of the adsorbed palladium
nanoparticles. The comparison of the XPS (see Table 3)
and spectrophotometry (see Table 4), as well as transmisꢀ
(
see Table 3). These results can suggest the different charꢀ
acter of the interaction of Pd nanoparticles with the PS
surface of nꢀ and pꢀtype of conductivity.
4
,7,8
sion and scanning microscopy
data shows that Pd
To specify the adsorption ability of PS of nꢀ and
pꢀtype of conductivity the spectrophotometric analysis of
reversed micelle palladium solutions in the course of forꢀ
nanoparticles are adsorbed both in the near surface PS
layer and in the pore volume of silicon matrix. The highꢀ
est adsorption is observed for the small size (< 10 nm)
mation of nanocomposites was carried out.
fractions of nanoparticles (ω = 1.5 and 5) on PS of
0
Previously3
,4,7,8,12
by using scanning electron microsꢀ
nꢀtype with the large pores (20—50 nm). For the PS
of pꢀtype with the smaller pores (5—20 nm) the adsorpꢀ
tion of nanoparticle proceeds mainly on the surface. There
can be guestꢀhost relationships between the sizes of preꢀ
cursor nanoparticles and those of the PS nanopores.
Let us try to explain the influence of porosity and
copy, AFM, HPLC and spectrophotometry we were able
to establish the character of Pd nanoparticles in the liquid
phase and on the surface of PS. In the wavelength interval
of 190—1000 nm Pd nanoparticles at ω = 1.5, 3 and 5
0
show two typical bands of plasmon absorption at
3
λ = 230—265 nm and λ = 290—320 nm. By comparing
solubilization extent on the character of the change of U
s
1
2
the solutions with the different extent of solubilization
the hypsochromic shift of the shortwave absorption band
value (see Tables 1, 2 and Fig. 1). The main reason of the
decrease in the U value is, probably, the partial atomic
s
(
λ = 240 nm) with the maximal integral intensity can be
ionization of Pd nanoparticles, which takes place due to
the specific adsorption on the surface in the volume of
PS nanopores. As a result of adsorption the formation
of electron deficient palladium nanoparticles on PS
recognized at ω = 5. Two main fractions of Pd nanoꢀ
0
particles correspond to two bands of plasmon absorption.
The particles with small sizes are in the range of 2 to 8 nm,
larger particles are 10—14 nm in size. Our data show, that
δ+
(Pd /Pd—Si) takes place, that leads to increasing work
adsorption on PS from the solutions with ω = 5 leads to
function of the surface electron and to decrease in U . The
0
s
the formation of spherical nanoclusters with sizes 10 nm
structural factor of the mutual compatibility of PS nanoꢀ
pores sizes and those of Pd nanoparticles during the forꢀ
mation of nanocomposites is important in the adsorpꢀ
tion—ionization cycle. Nanoparticles having dimensions
larger than diameters of PS pores cannot enter the pores.
The transfer of electron density from metalꢀcatalyst to
electron deficient matrixꢀcarrier is the common phenomꢀ
enon considered in the practice and the theory of heteroꢀ
geneous catalysis and is often used for the interpretation
of experimental data.9
or less. In the pools of micellar solutions with ω = 3 the
0
share of largeꢀsize fraction (10—14 nm) is the highest.
Adsorption on PS the Pd results in ellipsoidal nanoclusters
with the lateral sizes ranging from 10 to 40 nm and with
the height reaching 8 nm. For the nanoparticles with the
lowest sizes of the aqueous pool at ω = 1.5 the shares of
0
smallꢀ and largeꢀsize fractions are approximately equal.
When nanoclusters are formed from these solutions both
spherical particles with the sizes lower than 10 nm, and
chain structures with the cross section 5—10 nm and the
height up to 2 nm appear. This suggests a certain self
,14—16
1
4
For example, in a study of features of hydrogenolysis
of ethane, propane, cyclopropane, and isobutane it was
shown, that the reaction rate is dependent on the value of
3
,4,7,8
organization of Pd nanoparticles on the PS surface.
3
δ+
The results of the measurements of the integral intenꢀ
sity of the characteristic bands of plasmon absorption of
Pd nanoparticles (λ = 230—265 nm, λ = 290—320 nm),
the induced charge of palladium particles (Pd ) during
their interaction with the supports (zeolites and SiO ).
2
1
4
The study of interactions of methylcyclopentane made
it possible to determine that the increase in the reaction
rate is caused by the presence of electron deficient Pdδ+
1
2
which were obtained during adsorption on the surface of
PS of nꢀ and pꢀtype of conductivity within 72 hours, are

1
486
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
Yashtulov et al.
sites. On analysing the mechanism of electrocatalysis of
the binary Pdꢀbased systems in the oxidation of hydrogen
with CO admixtures, it was found that the rate of Н2
oxidation sharply increases when the large number of elecꢀ
tron deficient sites of Pd appear on the surface layer. The
features of catalysis of nanocomposites based on Au with
Pd, Ni, Co, and Fe immobilized on SiO and Al O in the
In this case the rateꢀlimiting step can be one of the
electrochemical steps (4) or (5). The second mechaꢀ
nism includes the heterolytic decomposition with the
1
7
electrooxidation of H molecule. In the presence of the
2
δ+
Pd /Pd—Si redoxꢀpair makes the involvement of heteroꢀ
lytic bond cleavage possible and the acceleration of the
electrochemical steps (4) and (5) can also be considered.
2
2
3
1
5
δ+
allyl isomerisation of allylbenzene, are explained by
appearance of positive charge on Au. The formation of
For example, when Pd ion is coordinated with Н molꢀ
2
ecule the following interactions occur:
δ+
partially charged clusters of Au , active in the isomerizaꢀ
Pdδ+ + (H2)ads
PdHδ–1
[PdHδ–1] + H+,
(6a)
tion is caused by the shift in electron density from Au to
electron deficient sites on the surface. The theoretical
evaluation16 of the mechanism of interaction of Pt nanoꢀ
particles with the semi conducting matrix resulted in
conclusion, that the appearance of the charges on the
Pd/semiconductor boundary is caused by redistribution
of electron density, that favors a decrease in the activation
energy in electrochemical reactions of oxidation of
hydrogenꢀcontaining reducing agents.
δ–1
+ H•
[
]
Pd
ads
Pdδ+ + H + 2 e .
+
–
(6b)
δ+
When Pd /Pd pair is coordinated sinchronously with
Н molecule the following interactions occur
2
Pd—Pdδ+ + H —H
–
+
[PdHδ–1] + Pd + H+,
(7a)
[
PdHδ–1] + Pd + H+
Pd—Pdδ+ + 2 H+ + 2 e–.
Let us consider the role of electron deficient Pdδ+
nanoparticles on PS in the electrocatalytic reactions of
the main reducing agents for FC. The Pd compounds are
used as anodes for FC first of all because palladium is
resistant to the presence of СО, which is the main cataꢀ
lytic poison for hydrogenꢀcontaining fuels. The formic
acid is one of the most promising fuels for micro power
electrical sources.2 In the FC with formic acid the anode
reaction of the direct oxidation of HCOOH occurs
without СО formation (dehydrogenation):
(7b)
The presence of PdHδ+ adducts were determined by
means of the lowꢀenergy electron diffraction during the
study of the mechanism of hydrogen adsorption, while
the effect of the substantial increase of the rate of
neopentane hydrogenolysis on the zeolite matrix was
,6
δ+
14
explained by the formation of PdH adducts.
Therefore, the results described above showed, that
electron deficient palladium nanocomposites form on the
surface of PS causing the decrease of the surface potential.
The charge state, concentration, size and the shape of
palladium nanocomposites are dependent on combinaꢀ
tion of the structure of nanopores of PS of nꢀ or pꢀtype
and the sizes of palladium nanoparticles in the course of
adsorption.
+
–
HCOOH
COOH + H + e
+
–
CO + 2 H + 2 e .
(1)
2
The elimination of the side reaction of the indirect
oxidation with the CO intermediate formation (deꢀ
hydratation)
HCOOH
COads + H O
CO + 2 H + 2 e
The work was financially supported by the Russian
Foundation for Basic Research (Projects Nos 09ꢀ08ꢀ00547
and 09ꢀ08ꢀ00758).
2
+
–
(2)
2
is based on action of the Pd catalyst. The presence of the
redoxꢀpair (Pd /Pd—Si), probably, favors catalytic oxiꢀ
dation of CO, which proceeds due to the transfer of elecꢀ
tron density to the electron deficient Pdδ+ nanoparticles:
δ+
References
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Pdδ+/Pd—Si + CO + H O
2
δ–2
+
Pd /Pd—Si + CO + 2 H .
(3)
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007, 52, 2506.
2
2
The rateꢀlimiting step of the electrocatalytic hydrogen
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2
followed by the step of rapid ionization.17 However at
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Technics], 2008, 8, 20 (in Russian).
some conditions the mechanism with the simultaneous
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5
. G. S. Mishra, S. Sinha, Catal. Lett., 2008, 125, 139.
H•
+
–
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A. Asthana, M. A. Shannon, R. Kenis, Sens. Actuators B:
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(
H ) + H O
+ H O + e ,
(4)
(5)
2
ads
2
ads
+
3
H• + H O
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Palladium nanocomposite catalysts on silicon
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