Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically
We have investigated the current creation accompanied by the water decomposition H₂O → OH + H caused by various catalytically active electrodes with different electrochemical potentials, both without external electric voltage on these electrodes and with the applied voltage V₀ = ±9.7 V. It is fou...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2007
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| Цитувати: | Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically / V.Ye. Primachenko, O.A. Serba, V.A. Chernobai, E.F. Venger // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 40-45. — Бібліогр.: 7 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1178912025-06-03T16:25:26Z Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically Primachenko, V.E. Serba, O.A. Chernobai, V.A. Venger, E.F. We have investigated the current creation accompanied by the water decomposition H₂O → OH + H caused by various catalytically active electrodes with different electrochemical potentials, both without external electric voltage on these electrodes and with the applied voltage V₀ = ±9.7 V. It is found that the current value and its time dependence are essentially influenced by such factors as thermal and natural (in ambient atmosphere) oxidation of electrodes (made of Al, Si, Yb, Ni, Ti, Cr₃Si, and Ni₃Si), changing their relief (texturing, polishing), and the electrolytic deposition of palladium as an impurity on the surface (Ti, Cr₃Si). Changes in the current caused by the above factors are realized as a consequence of changes in both the electron work function inherent to these electrodes and their catalytical activity concerning the water decomposition both in the absence and the presence of the external voltage V₀. 2007 Article Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically / V.Ye. Primachenko, O.A. Serba, V.A. Chernobai, E.F. Venger // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 40-45. — Бібліогр.: 7 назв. — англ. 1560-8034 PACS 81.16.Hc, 82.30.Lp, 82.45.Fk https://nasplib.isofts.kiev.ua/handle/123456789/117891 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
We have investigated the current creation accompanied by the water
decomposition H₂O → OH + H caused by various catalytically active electrodes with
different electrochemical potentials, both without external electric voltage on these
electrodes and with the applied voltage V₀ = ±9.7 V. It is found that the current value and
its time dependence are essentially influenced by such factors as thermal and natural (in
ambient atmosphere) oxidation of electrodes (made of Al, Si, Yb, Ni, Ti, Cr₃Si, and
Ni₃Si), changing their relief (texturing, polishing), and the electrolytic deposition of
palladium as an impurity on the surface (Ti, Cr₃Si). Changes in the current caused by the
above factors are realized as a consequence of changes in both the electron work function inherent to these electrodes and their catalytical activity concerning the water
decomposition both in the absence and the presence of the external voltage V₀. |
| format |
Article |
| author |
Primachenko, V.E. Serba, O.A. Chernobai, V.A. Venger, E.F. |
| spellingShingle |
Primachenko, V.E. Serba, O.A. Chernobai, V.A. Venger, E.F. Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Primachenko, V.E. Serba, O.A. Chernobai, V.A. Venger, E.F. |
| author_sort |
Primachenko, V.E. |
| title |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| title_short |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| title_full |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| title_fullStr |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| title_full_unstemmed |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| title_sort |
influence of some physico-chemical factors on properties of electrodes that decompose water catalytically |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2007 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/117891 |
| citation_txt |
Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically / V.Ye. Primachenko, O.A. Serba, V.A. Chernobai, E.F. Venger // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 40-45. — Бібліогр.: 7 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT primachenkove influenceofsomephysicochemicalfactorsonpropertiesofelectrodesthatdecomposewatercatalytically AT serbaoa influenceofsomephysicochemicalfactorsonpropertiesofelectrodesthatdecomposewatercatalytically AT chernobaiva influenceofsomephysicochemicalfactorsonpropertiesofelectrodesthatdecomposewatercatalytically AT vengeref influenceofsomephysicochemicalfactorsonpropertiesofelectrodesthatdecomposewatercatalytically |
| first_indexed |
2025-11-27T15:37:53Z |
| last_indexed |
2025-11-27T15:37:53Z |
| _version_ |
1849958465980596224 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
40
PACS 81.16.Hc, 82.30.Lp, 82.45.Fk
Influence of some physico-chemical factors on properties
of electrodes that decompose water catalytically
V.E. Primachenko, O.A. Serba, V.A. Chernobai, E.F. Venger
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prosect Nauky, 03028 Kyiv, Ukraine, e-mail: pve18@isp.kiev.ua
Abstract. We have investigated the current creation accompanied by the water
decomposition H2O → OH + H caused by various catalytically active electrodes with
different electrochemical potentials, both without external electric voltage on these
electrodes and with the applied voltage V0 = ±9.7 V. It is found that the current value and
its time dependence are essentially influenced by such factors as thermal and natural (in
ambient atmosphere) oxidation of electrodes (made of Al, Si, Yb, Ni, Ti, Cr3Si, and
Ni3Si), changing their relief (texturing, polishing), and the electrolytic deposition of
palladium as an impurity on the surface (Ti, Cr3Si). Changes in the current caused by the
above factors are realized as a consequence of changes in both the electron work function
inherent to these electrodes and their catalytical activity concerning the water
decomposition both in the absence and the presence of the external voltage V0.
Keywords: catalytically active electrodes, oxidation, water decomposition.
Manuscript received 20.10.06; accepted for publication 24.04.07; published online 19.10.07.
1. Introduction
One of the actual up-to-date problems is the power
production with minimum injury to the ecology of
ambient medium and minimum economic expenses. An
example of solving this problem is the use of the
difference of electrochemical potentials that is set by the
nature in different substances or created, or changed in
them, including the synthesis of new substances.
In our previous works [1-3], we studied the
phenomenon of electric current creation accompanied
with water decomposition H2O → OH + H when dipping
two electrodes with different electrochemical potentials
into it, these electrodes (at least one of them) being a
catalyst of the decomposition of water molecules.
As shown in these works [1-3], the catalytic
decomposition of water is mainly realized due to the
presence of physico-chemical inhomogeneities on the
micro(nano) scale on the electrode surface and to strong
electric fields existing there. In particular, we studied the
influence of thermal oxidation of catalytically active Si-
based electrodes on current magnitudes and time
dependences inherent to these electrodes and
counterelectrodes made of Al, Yb, Pt [3].
This work is devoted to the influence of electrodes
made of Al, Yb, Ni, Ti, and Cr3Si on water
decomposition. In addition, a considerable attention was
paid to studying such factors as a change of the electrode
relief (texturing, grinding, and polishing) and the
electrochemical deposition of Pd on Ti, Cr3Si electrodes.
2. Experimental
The method of our experiments was described in works
[1-3] in detail. When dipping two different electrodes
into distilled water simultaneously, there arises the
difference of potentials ∆Vk between them, which, as a
rule, is less than the difference between the electron
work functions for these electrodes ∆φ (this difference
∆φ is equal to the difference between the electro-
chemical potentials of electrodes). After making the
external electric circuit to be closed (the time t = 0), we
measured time dependences for the current, J(t).
Since the area of electrodes S and the distance
between them L for various electrode pairs are different,
we compare the efficient conductivities σ = J(t)(L / ∆Vk S)
= AJ(t) of the electrochemical systems, where A =
= L /(∆Vk S) V−1cm−1. When the electric circuit was
supplied with the additional external voltage V0 = ±9.7 V,
we used the value (∆Vk ± V0) instead of the value ∆Vk.
Thermal oxidation of electrodes was realized at Т =
= 450 °С for 4 h in dry О2, while natural oxidation took
place under ambient atmospheric conditions and by
applying these electrodes as anodes. The relief of
electrodes was changed using emery-paper (for
grinding), diamond paste on felt (for polishing), as well
as using anisotropic chemical etching (texturing).
Before measuring the σ = AJ(t) dependence, we
determined the electron work function inherent to the
electrodes in use. To this end, we used a standard
reference electrode made of Pt (φ = 5.32 eV) [4], as Pt is
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
41
the most chemically stable electrode in our inves-
tigations. The values of φ for various electrodes were
determined via calculations made after measuring the
current between Pt and the investigated electrode in the
forward and backward directions [1-3] and are presented
in the table.
3. Experimental results and discussion
In our investigations, the electrode made of Yb that
possesses a relatively low electron work function was
mostly used as anode [1-3]. It is known (see, in
particular, [1]) that, when Yb is oxidized, the values of
AJ(t) are increased to some extent despite the growth of
φ. Therefore, we studied first the changes of φ and AJ(t)
which accompany the changes of an Yb surface state.
Fig. 1 shows the obtained dependences AJ(t) at V0 = 0
for three states of the Yb surface: (i) naturally oxidized
(initial) (curve 1); (ii) polished (curve 2); (iii) oxidized
for three months when it is operating as anode (curve 3)
after polishing.
As seen from Fig. 1, the dependences AJ(t)
noticeably differ from each other only within the first 20
min after bridging the Yb and Pt electrodes. This is
related both to different φ values (and ∆Vk, respectively)
and the dependence of the catalytic activity of the Yb
electrode on the degree of oxidation. As seen from the
table, the values of φ were as follows: 3.65, 3.04, and
3.67 eV, while ∆Vk were equal to 0.86, 1.37, and 0.85 V.
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
5
10
15
20
t,min
,
1
3
2
Fig. 1. Time dependences of the efficient conductivity AJ(t)
when water is decomposed using the pair of electrodes Yb-Pt.
The Yb electrode is: 1 – naturally oxidized; 2 – as polished; 3 –
oxidized after polishing and operation for 3 months.
Table. The electron work functions φ for electrodes in various
physico-chemical states.
Electrode Electrode
symbol φ, eV
Aluminum as grinded AlGr
СВ 4.12
Aluminum grinded and aged AlGr
AG 4.3
Aluminum plain and aged AlP
AG 4.57
Aluminum AlP
AG after thermal
oxidation AlP
ТО 5.11
Aluminum textured and aged AlТAG 4.58
Aluminum AlТAG after thermal
oxidation AlТAG 5.12
Nickel (plane) Ni 4.82
Nickel thermally oxidized NiTO 4.97
Chromium silicide Cr3Si 4.43
Chromium silicide after thermal
oxidation Cr3SiТО 5.44
Chromium silicide after Pd doping
(1.5·1016 cm−2)
Cr3Si
〈Pd1〉
4.53
Chromium silicide after Pd doping
(1·1018 cm−2)
Cr3Si
〈Pd5〉
6.24
Titanium as grinded TiGr
СВ 4.38
Titanium grinded and aged TiGr
AG 5.15
Titanium doped with Pd (2·1016cm−2) Ti〈Pd1〉 5.17
Titanium doped with Pd (1·1018cm−2) Ti〈Pd4〉 5.30
Titanium TI〈Pd4〉 thermally oxidized Ti〈Pd4〉ТО 5.42
Silicon textured and aged SiТAG 4.85
Silicon SiТAG after treatment in HF SiТHF 4.76
Ytterbium aged YbAG 3.65
Ytterbium polished YbP 3.04
Ytterbium YbP after 1-month operation
as anode (oxidized) YbОX 3.67
Nickel silicide Ni3Si 4.85
Ni3Si after thermal oxidation Ni3SiТО 4.88
Considering the obtained data, it seems reasonable
to make the following conclusions: (i) when measuring
the AJ(t) dependences 20 min after the circuit closing,
the values of AJ(t) are practically the same, i.e., the
oxidizing degree of the Yb electrode does not influence
its stable functioning; (ii) catalytic activity of the Yb
electrode at t < 0 and for the first minutes of the current
transfer increases with its oxidation degree. It is not
surprising, because not only the transition metals with
their internal unfilled electron shells but also their oxides
are catalytically active in reduction reactions (it is this
reaction that provides water decomposition).
It is seen from the table that oxidation of all the
electrodes in air and in the course of exploitation causes
the growth of φ which is more pronounced after thermal
oxidation of electrodes. In most cases, thermal oxidation
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
42
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
10
20
30
2(-)
4(+)
3(-)
3(+)
1(-)
2(+)
1(+)
t,min
,
1
2
4
3
Fig. 2. AJ(t) dependences for the electrode pairs AlT
TO-Yb (1,
1(+), 1(−)), NiTO-Yb (2, 2(+), 2(−)), Cr3SiTO-Yb (3, 3(+), 3(−)),
Ti〈Pd4〉TO-Yb (4, 4(+)). The curves 1, 2, 3 and 4 were obtained
at V0 = 0, curves marked with signs (+) and (−) at V0 = ±9.7 V
on the Yb electrode, respectively.
induces also the growth of AJ(t). Fig. 2 shows these
dependences for thermally oxidized electrodes AlT
TO,
NiTO, Gr3SiTO, and Ti〈Pd4〉TO coupled with the aged Yb
electrode. The superscripts (+) and (–) indicate the AJ(t)
dependences when the voltages V0 = ±9.7 V are applied,
respectively, to the Yb electrode.
Curves 1-4 were obtained at V0 = 0. Comparing the
dependences in Fig. 2 with the respective ones obtained
before thermal oxidation of electrodes (in work [2] and
in this one), we can draw conclusion that thermal
oxidation increases the AJ(t) values (excluding the
dependence for Ti〈Pd4〉TO) and often changes the
character of their time dependences. It is indicative of
the changes in the processes of catalytic decomposition
of water molecules on electrodes as a consequence of the
creation of oxide films thermally grown on them.
A natural oxide film can provide the current
creation along with water decomposition in some other
way as compared to the thermally grown one. It was
shown in [3] that a thermally grown film on Si increases
the electron work function up to 10…11 eV and essen-
tially changes the AJ(t) dependences when the Si ele-
ctrode is coupled with Al, Yb, and Pt counterelectrodes.
As seen from the table, the HF etching of the
natural oxide film on a textured silicon electrode SiT
AG
aged for 10 years [6] changes φ only a little (from 4.85
down to 4.76 eV), while the character of the AJ(t)
dependences is changed noticeably (Fig. 3a and b), but
in another manner as compared to that in [3].
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
10
20
2(+)
2(-)
1(+)
1(-)
t,min
1
2
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
10
20
2(-)
2(+)
1(-)
1(+)
,
t,min
1
2
Fig. 3. AJ(t) dependences for the electrode pairs SiT-Pt (a) and
SiT-Yb (b). The curves 1, 1(+), 1(−) were obtained using aged
textured silicon SiT
AG, curves 2, 2(+), 2(−) – after treating it in
HF (SiT
HF). 1, 2 – at V0 = 0; 1(+), 2(+) and 1(−), 2(−), at V0 = ±
9.7 V on the SiT electrode, respectively.
If the Pt electrode is coupled with the SiT electrode
playing the role of an anode, curves 2, 2(+), and 2(−)
(measured after etching the oxide film) possess some
higher AJ(t) values as compared to the respective values
for curves 1, 1(+), and 1(−) for the SiT
AG electrode with the
oxide film. In the pair with the Yb electrode where the
SiT electrode serves as cathode, curves 1 and 1(+) possess
lower AJ(t) values as compared with those for curves 2,
2(+) curves only in the initial parts of the time
dependences. At t > 20 min, curve 1 is located above
curve 2, as well as curve 1(+) is above curve 2(+) at t > 6
min. All these results indicate the changes in features of
catalytic water decomposition both after deletion of the
oxide film on the SiT electrode and after changing its role
(anode or cathode).
The essential role of a relief and thermal oxidation of
the Al electrode in the character of AJ(t) dependences for
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
43
the pair Al-Pt is illustrated in Fig. 4. Curves 1' and 2' were
obtained, respectively, on the plane AlPAG and textured
AlTAG electrodes, both being aged in ambient air.
It is seen that the preliminary texturing of Al in an
electrochemical bath with a chlorine salt solution
considerably increases the catalytic activity of the Al
electrode, which increases AJ(t). The latter value can be
further increased in the course of thermal oxidation of
AlP
AG and AlТAG electrodes (see curves 1, 1(+), and 1(−) as
well as 2, 2(+) and 2(−), respectively). The considerable
distinction between curves 1(+) and 1(−) as compared with
curves 2(+) and 2(−) indicates a considerable role of the
electric field effects inherent to non-uniformities of the
relief when decomposing molecules of water on the Al
electrode.
Faster catalytic decomposition of water can be
obtained not only by texturing the Al electrode but by its
grinding, which is especially clear pronounced for the
first 10 min of the decomposition. This is evident from
the comparison of curves 2' and 1'
Gr obtained,
respectively, for the textured and grinded Al electrodes.
Grinding the electrode made of nickel silicide Ni3Si
increases the AJ(t) values by 1.5-2 times, when it is used
as cathode coupled with the AlP
AG anode. Grinding the
Ti electrode (cathode) also increases twice the AJ(t)
values obtained in the pair with the Yb electrode
(anode).
The electrode made of a precious metal (Pt) can be
successfully substituted with the electrode from thermally
oxidized chromium silicide Cr3SiTO that possesses φ =
5.44 eV. In Fig. 5, we show the AJ(t) dependences for the
pairs AlP
AG-Cr3SiTO (curves 1, 1(+), and 1(−)), as well as
those for AlTTO-Cr3SiTO (curves 2, 2(+), and 2(−)). It can be
seen that the AJ(t) values in Fig. 5 are considerably higher
than those in Fig. 4, especially for the pair AlTTO-Cr3SiTO.
In our opinion, metal silicides are rather promising as
cathodes for the more efficient current creation based on
water decomposition.
The time dependence AJ(t) at V = 0 obtained for the
grinded ТіGr electrode (cathode) coupled with the Yb
electrode is shown in Fig. 6 with curve 0. When the
measurements last up to 2 h, the AJ(t) values increase up
to 21·10-6 Ohm−1cm−1, ∆Vk being increased only from
+1.14 to +1.19 V (sign (+) on the Yb electrode).
In Fig. 6, curves 1, 2, 3, and 4 were obtained using
the Yb electrode (anode) coupled with the ТіGr electrode
(cathode) covered via step-by-step deposition by the Pd
impurity with the following concentrations: 2·1016,
2·1017, 5·1017, and 1·1018cm−2, respectively. In the course
of deposition, Al served as anode. In this case, the φ
values determined relatively to the Pd electrode grew
from 5.17 up to 5.39 eV. As seen from Fig. 6, at low
concentrations (2⋅(1016…1017) cm−2) of Pd deposited on
the grinded ТіGr electrode, the AJ(t) values are decreased
(curves 1 and 2 as compared with curve 0). This means
that, at the very beginning, Pd atoms neutralize
catalytically active centers of a structural character,
which arise after grinding.
A further growth of the concentration of deposited
Pd impurity results in the creation of new catalytically
active Pd centers which enhance the AJ(t) values (curves
3 and 4). Curve 4(−) obtained after applying the voltage
V0 = −9.7 V to the ТіGr〈Pd4〉 electrode evidences a
considerable growth of the catalytic activity inherent to
the ТіGr electrode doped with Pd in the presence of
strong local electric fields on its surface.
0 10 20 30
0
5
10
15
20
2(-)
2(+)
1(-)
1(+)
AJ,10-6Om-1cm-1
t,min
1
2
Fig. 5. AJ(t) dependences for the electrode pairs AlP
AG-Cr3SiTO
(1, 1(+), 1(−)) and AlТТО-Cr3SiTO (2, 2(+), 2(−)).The curves 1, 2
were obtained at V0 = 0; the signs (+) and (−) correspond to
V0 = ±9.7 V on the Al electrode.
0 10 20 30
0
5
10
1'
1
1(-)
1(+)
2(+)
2(-)AJ,10-6Om-1cm-1
t,min
1
1'
2
2'
'
Fig. 4. AJ(t) dependences for the electrode pairs AlP
AG-Pt
(1'), AlТAG-Pt (2'), AlP
ТО-Pt (1, 1(+), 1(−)), AlТТО-Pt (2,
2(+), 2(-)), AlGr
СВ-Pt (1'
Gr). The curves 1', 2', 1, 2, 1'
Gr at
V0 = 0; the signs (+) and (−) correspond to V0 = ±9.7 V on
the Al electrode.
AJ, 10–6 Ohm–1 cm–1 AJ, 10–6 Ohm–1 cm–1
1′Gr
1′Gr
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
44
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
10
20
30
4(-)
,
t,min
4
3
1
2
0
Fig. 6. AJ(t) dependences for the electrode pair TiGr〈Pd〉-Yb.
The curve 0 was obtained for the pair TiGr
СВ-Yb in absence of
Pd impurity, curve 1 – Pd (2·1016cm−2), 2 – Pd (2·1017cm−2),
3 – Pd (5·1017cm−2), 4 – Pd (1·1018cm−2), 4(−) − V0 = –9.7 V on
the electrode TiGr〈Pd4〉.
The highest AJ(t) values were obtained when using
the Yb electrode as anode and Cr3Si as cathode that was
preliminarily covered electrolytically with the Pd
impurity up to the concentration close to 1·1018 cm−2.
Fig. 7 illustrates the AJ(t) dependences for the pair Yb-
Cr3Si without doping Cr3Si with Pd (curve 0), when the
concentration of the doping impurity is equal to
1.5·1016 cm−2 (curve 1), as well as for the maximal
concentration of the Pd impurity of 1·1018 cm−2 (curves
2, 2(+), and 2(−)).
Moreover, in the catalytic water decomposition, an
essential role is played by not only the Cr3Si〈Pd5〉
electrode but the Yb electrode as well, since the
substitution of it with the AlP
AG electrode results in
considerably lower AJ(t) values (curves 3, 3(+), and 3(−)).
The signs (+) and (−) marking curves in Fig. 7 mean the
application of respective potentials, V0 = ±9.7 V, to the
Yb or Al electrode.
When studying the current transfer provided by the
pair Yb-Cr3Si〈Pd5〉 for 2 h at V0 = 0, we observed the
growth of AJ(t) values up to 100·10−6 Ohm−1cm−1. It is
our highest value among those in works [1-3]. This
means the creation of a current source with a current
density close to 120 µA·cm−2 and the potential difference
between the electrodes ∆Vk = +1.8 V, i.e., the power of
this electrochemical system is close to 0.216 mW per
1 cm2 of the Cr3Si〈Pd5〉 electrode area. Note that the
value ∆Vk = +1.8 V was the same both at t = 0 and
t = 2 h.
AJ, 10–6 Ohm–1 cm–1
0 10 20 30
0
50
100
150
3(+)
3(-)
2(+)
2(-)
,
t,min
0
1 3
2
Fig.7. AJ(t) dependences for the electrode pairs Yb-Cr3Si〈Pd〉
(curves 0, 1, 2, 2(+), 2(−)) and AlP
AG-Cr3Si〈Pd5〉 (curves 3,
3(+), 3(−)). The curves 0, 1, 2, 3 were obtained at V0 = 0; the
signs (+) and (−) correspond to V0 = ±9.7 V on the Yb and Al
electrodes. The Cr3Si electrode was doped with Pd: 0 (Pd = 0);
1 (Pd = 1.5·1016cm−2); 2, 3 (Pd = 1·1018cm−2).
This means that the growth of AJ(t) values from
33·10−6 Ohm−1⋅cm−1 (t = 0) up to 100·10−6 Ohm−1cm−1
(t = 2 h) is realized due to the increase in the catalytic
activity of electrodes (first of all, that of the Cr3Si〈Pd5〉
electrode, because the Yb electrode activity is constant
in the system Yb-Pt (Fig. 1) at t > 20 min and does not
practically depend on its oxidation degree). Curves 2(+)
and 2(−) corresponding to the maximum AJ(t) values
confirm the essential influence of an electric field
present on non-uniformities of doped Pd and on porous
Cr3Si on the water decomposition.
In [2], we have already estimated the recovered
energy as a result of the water decomposition in accord
with the reaction Н2О ↔ ОН + Н: 5.1 eV per one Н2О
molecule [7]. However, in [2], we did not take into
account the recovered energy (power) due to the current
creation. Let us estimate a power gain under these
conditions by taking into account both the current
creation and the hydrogen output that can be also used
for the energy yield.
The calculations made following the way described
in [2] show that a current density of 120 µA·cm−2
provides the release of approximately 6·1012 OH and H
particles per one second. Their recombination in the
course of the reaction Н + ОН → Н2О provides the
power close to 4.8·10−3 mW, which is 45 times less than
the value obtained due to the current (0.216 mW). Thus,
the main source to recover energy in this process is the
current, rather than the hydrogen output.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 40-45.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
45
Conclusions
1. We have investigated the time dependences for the
current that arises between two electrodes with
different electrochemical potentials when changing
their catalytic activity as to the water
decomposition by using the following physico-
chemical factors: natural and thermal oxidation of
electrodes, changing the character of their relief
(chemical structuring, grinding, polishing), and the
electrolytic deposition of a catalytically active Pd
impurity onto electrodes.
2. It was found that natural (as well as in the course of
operation) oxidation of the Yb electrode most often
used as anode due to the low electron work
function does not practically influence the current
after 20 min since abridging the Yb-Pt electrodes.
3. Thermal oxidation (450 ºС, 4 h in dry О2) of
electrodes (Al, Ti, Ni, Cr3Si) increases the electron
work function for them and, as a rule, enhances the
current between them and a counterelectrode (Yb,
Pt, Al) both in the absence of an external voltage
and at V0 = ±9.7 V.
4. The chemical structuring of the electrode (Al, Si)
surface and the mechanical processing (grinding,
polishing) of the electrodes (Al, Ti, Cr3Si, Ni3Si,
Yb, Si) change the electron work function for these
electrodes and their catalytic activity as to the water
decomposition due to changes in the structure of
the electrode surface and a natural oxide film
covering them.
5. As a rule, structuring the electrode surface results
in the acceleration of the catalytic water
decomposition both at V0 = 0 and at V0 = ±9.7 V,
which indicates an essential influence of the strong
electric field arising at micro(nano)-
nonuniformities of the electrode structure on water
decomposition.
6. The best current creation (at V0 = 0) was observed
in the case of the pair Yb-Cr3Si〈Pd5〉, when the
current density reaches 120 µA·cm−2 at the voltage
between the electrodes ∆Vk = 1.8 V. It has been
calculated that the energy recovered due to the
current creation is considerably higher (by tens of
times) than that obtained with the use of reduced
hydrogen.
References
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