Mechanochemical approach for fabrication of a nano-structured NiO-sensing electrode used in a zirconia-based NO2 sensor

Article abstract of DOI:10.1016/j.electacta.2010.06.084

Highly uniform NiO nano-particles with a crystallite size of about 3 nm were obtained by room-temperature ball-milling of the parent Ni(OH)₂, which was derived using a sol-gel method. The obtained nano-structured NiO precursor was then utilized for the fabrication of NiO-sensing electrodes (SEs), which were further examined in the mixed-potential-type YSZ-based planar NO₂ sensor. The obtained results revealed the attractive advantages for the application of mechanochemical approach in regard to achieve high NO₂ sensitivity, NO₂ selectivity and reproducibility. All of the evaluated sensors attached with the nano-structured NiO-SEs, regardless of its sintering temperature, were found to exhibit high NO₂ sensitivity at 800°C under the wet condition (5 vol.% water vapor). In addition to high NO₂ sensitivity, the sensor attached with 1100°C-sintered NiO-SE showed highly selective properties towards NO ₂. The observed improvement in NO₂-sensing characteristics as well as the attainment of highly reproducible behavior for different sensor devices is discussed based on morphological and electrochemical observations of the studied sensors.

Full text of DOI:10.1016/j.electacta.2010.06.084

Electrochimica Acta 55 (2010) 6941–6945
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Mechanochemical approach for fabrication of a nano-structured NiO-sensing
electrode used in a zirconia-based NO sensor
2
a,∗
b
c,1
Vladimir V. Plashnitsa , Vinay Gupta , Norio Miura
a
Research and Education Center of Carbon Resources, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan
Carbon Technology Unit, Engineering Materials Division, National Physical Laboratory, New Delhi 110012, India
Art, Science and Technology Center for Cooperative Research, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 May 2010
Received in revised form 29 June 2010
Accepted 29 June 2010
Available online 25 July 2010
Highly uniform NiO nano-particles with a crystallite size of about 3 nm were obtained by room-
temperature ball-milling of the parent Ni(OH)2, which was derived using a sol–gel method. The obtained
nano-structured NiO precursor was then utilized for the fabrication of NiO-sensing electrodes (SEs),
which were further examined in the mixed-potential-type YSZ-based planar NO2 sensor. The obtained
results revealed the attractive advantages for the application of mechanochemical approach in regard to
achieve high NO2 sensitivity, NO2 selectivity and reproducibility. All of the evaluated sensors attached
with the nano-structured NiO-SEs, regardless of its sintering temperature, were found to exhibit high
Keywords:
NOx sensor
Mixed-potential
YSZ
◦
NO2 sensitivity at 800 C under the wet condition (5 vol.% water vapor). In addition to high NO2 sensitiv-
◦
ity, the sensor attached with 1100 C-sintered NiO-SE showed highly selective properties towards NO2.
NiO
Ball-milling
The observed improvement in NO2-sensing characteristics as well as the attainment of highly repro-
ducible behavior for different sensor devices is discussed based on morphological and electrochemical
observations of the studied sensors.
©
2010 Elsevier Ltd. All rights reserved.
1
. Introduction
reported in the last decade [8–13]. Among them, special empha-
sis has been paid to the design, construction and comprehensive
investigation of stabilized-zirconia-based NOx sensors coupled
with metallic- or metal oxide-based sensing electrodes (SEs)
[12,14–30]. Because engine temperature may occasionally reach
To satisfy the current automobile emission regulations enforced
by the European Union, the United States and Japan [1–3], an on-
board diagnostic (OBD) system for vehicles has been proposed that
would monitor most of the components related to air pollution. The
OBD system is composed a three-way catalyst (TWC) to reduce con-
centrations of exhausted non-methane hydrocarbons (NMHCs), CO
◦
even 800–900 C during vehicle acceleration, zirconia-based sen-
sors should be capable of providing rather high sensitivity and
selectivity against NO at these high operating temperatures above
2
◦
and nitrogen oxides (NO and NO , collectively referred as NOx). In
800 C. Recently, in the process of screening for a metal oxide-SE,
2
addition, to compensate for the low NOx-removal capability of the
TWC under lean-burn (air-rich) conditions, a NOx-storage catalyst
and a urea-based selective-catalytic reduction (SCR) system have
been recently proposed and developed [4–7]. Therefore, to con-
trol the efficiency of these catalytic converters, to detect catalyst
decay and to monitor residual concentrations of NOx gases released
through the tailpipe, reliable high-performance NOx sensors are
required.
a mixed-potential-type yttria-stabilized-zirconia (YSZ)-based sen-
sor using a NiO-SE was found to provide a sensitive response to
NO2 even at operating temperatures of 800–850 C [31]. To gain
◦
such a high sensitivity and selectivity against NO , the NiO-SE
2
◦
should be sintered at relatively high temperatures of 1300–1400 C
[12,20,31,32]. There were several later attempts to decrease the sin-
tering temperature of the NiO-SE by adding a second component
(dopant) maintaining its high performance towards NO2 [33,34].
However, it should be pointed out that any second and/or more
doping components make the fabrication of the SE more compli-
cated and may affect the reproducibility and long-term stability of
its gas-sensing characteristics. Thus, it seems that use of a pure
oxide-SE in YSZ-based sensors would be attractive solution for
meeting current sensor requirements, such as high gas sensitivity
and selectivity, excellent reproducibility and long-term stability.
These sensors are also ideal for mass production because of their
relatively simple fabrication and low cost. More importantly, as the
Taking into consideration rather harsh conditions for
a
practical sensor operation (high temperature, high humidity,
multi-component gas mixtures), various solid-electrolyte-based
electrochemical NOx-sensing devices have been studied and
∗ Corresponding author. Tel.: +81 92 583 7886; fax: +81 92 583 8976.
E-mail address: plachnit@astec.kyushu-u.ac.jp (V.V. Plashnitsa).
ISE member.
1
0
013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.06.084

6
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V.V. Plashnitsa et al. / Electrochimica Acta 55 (2010) 6941–6945
reproducibility of the gas-sensing characteristics of YSZ-based sen-
sors largely depends on SE morphology, attention should be focused
on the fabrication of morphologically uniform oxide-SEs. One of the
potential ways to accomplish this goal could be the preparation of
highly homogeneous oxide precursors followed by the utilization
of these precursors in the SE fabrication process.
Quite recently, we have found that the application of a ball-
milling approach for the fabrication of a NiTiO -SE resulted in
3
an improvement in the reproducibility of the YSZ-based HC
(
propylene) sensors [35]. Thus, in the present study, the highly
homogeneous nano-structured NiO precursor was obtained by ball-
milling at room temperature followed by its utilization as a SE in a
YSZ-based NO sensor. As a result, the sensor using the NiO-SE that
2
◦
was sintered at 1100 C showed a sensitive and selective response
to NO . In addition to improving the NO -sensing characteristics,
2
2
the application of this mechanochemical approach enhanced the
reproducibility of sensing performance for the fabricated NO2 sen-
sors.
2
. Experimental
A tape-casted YSZ (8 mol.%-doped Y O ) plate (10 mm × 10 mm,
2
3
0
.2 mm in thickness) was utilized for fabrication of the sensor. Using
a planetary ball-mill (Pulverisette 7, Fritsch GmbH, Germany), the
nano-structured NiO powder was obtained by ball-milling the par-
ent powdered Ni(OH)2 precursor using zirconia balls (2 mm in
diameter) in ethanol solution at 2000 rpm at room temperature for
Fig. 1. XRD patterns of (a) the parent Ni(OH)2 powder derived from a sol–gel method
and (b) the nano-structured NiO powder obtained by ball-milling of the Ni(OH)2 at
room temperature.
3
h. The powdered Ni(OH)2 precursor was prepared by a precipita-
+
100 mV at a constant scan rate of 2 mV/min using a two-electrode
tion method; 0.5 M NaOH solution (Wako Pure Chemical Industries,
Ltd., Japan) was added drop-wise to a solution of highly purified
nickel nitrate (Ni(NO ) ·6H O; Wako Pure Chemical Industries,
configuration.
3
2
2
Ltd., Japan) followed by washing in distilled water and drying at
3. Results and discussion
◦
1
30 C overnight. The X-ray diffraction patterns of both synthe-
sized powders were obtained by an X-ray diffractometer (XRD,
Fig. 1 shows the XRD patterns for (a) the parent Ni(OH) sample
2
RINT 2100VLR/PC, Rigaku Corp., Japan) using Cu K␣ radiation in a
obtained using the precipitation method and (b) the NiO powder
prepared by ball-milling at room temperature. The XRD patterns
of the Ni(OH)2 indicate that the parent compound crystallized in
a hexagonal (theophrastite, P-3m1, JCPDS no. 14-0117) structure
with all of the characteristic peaks. Additional peaks due to pos-
sible impurities were not observed. The well crystalline structure
of the parent Ni(OH)2 could be attributed to the fact that the pre-
◦
◦
◦
plane ꢀ/2ꢀ geometry between 10 and 90 at a scan rate of 1 /min.
The prepared nano-structured NiO powder was mixed with ␣-
terpineol organic binder and the resulting paste was screen-printed
onto the front side of the YSZ to form an NiO-SE with an aver-
age thickness of about 4 ␮m. The NiO-printed YSZ plates were then
◦
◦
◦
sintered at 800 C, 1100 C and 1400 C for 2 h in air. The Pt layer
fabricated on the back side of the YSZ plate was used as a ref-
erence electrode (RE). The morphology of the obtained NiO-SEs
was observed using field-emission scanning-electron microscopy
◦
cipitated powder was dried at a temperature of 130 C overnight.
It should be pointed out that nano-sized NiO may be convention-
ally prepared by the thermal decomposition of the parent Ni(OH)2
◦
(
FE-SEM, JSM-6340F, JEOL Ltd., Japan).
at temperatures above 400 C [33]. However, in the present case,
The fabricated planar sensors were assembled in a quartz tube,
the pure, highly homogeneous nano-structured NiO powder was
mechanochemically obtained even at room temperature through
the use of ball-milling approach. The XRD patterns of obtained
NiO product (Fig. 1(b)) show broad peaks, indicating the nano-
sized dimensions of the NiO particles. NiO was crystallized in a
cubic (bunsenite, Fm3m) structure with the unit-cell parameter
(a) of 4.117 Å (JCPDS no. 47-1049). The size of the NiO crystallites
estimated by the Scherrer’s equation was calculated to be approx-
imately 3 nm. More importantly, no peaks for the parent Ni(OH)2
were found, indicating that highly purified nano-structured NiO
powder could be obtained even at room temperature.
placed in an electric furnace and connected to a conventional gas-
flow apparatus. The gas-sensing characteristics of the sensors were
◦
examined at 800 C. Both the NiO-SE and the Pt-RE were simulta-
neously exposed to the wet base gas (5 vol.% O + 5 vol.% H O + N
2
2
2
balance) or to the sample gas that was prepared by diluting each of
parent gas (CO, CH , C H , NO and NO ) with the base gas. For the
4
3
8
2
selectivity tests, the concentrations of all of the examined gases
in the sample gas were kept constant at 400 ppm. The gas-flow
rate was fixed at 100 ml/min. The dependence of the NO2 sensitiv-
ity was evaluated in the NO2 concentration range of 50–400 ppm.
The electromotive force (emf) output between the NiO-SE and the
Pt-RE of the sensor was monitored as a sensing signal with a dig-
ital electrometer (R8240, Advantest Corp., Japan). The sensitivity
Since it is well-known that the morphology of the NiO-SEs used
in mixed-potential-type YSZ-based sensors greatly affects their
gas-sensing characteristics [12,32], the utilization of highly homo-
geneous powdered NiO is likely to achieve a uniform morphology
of the NiO-SEs during the sintering process at high temperatures.
The good uniformity of the obtained NiO-SEs will thus result in
obtaining the reproducible gas-sensing characteristics of the YSZ-
based sensors. Fig. 2 shows the representative SEM images for the
(
ꢁemf) to each gas was defined as the difference between the emf
value of the sensor in the sample gas (emfsample) and that in the
base gas (emfbase). The measurements of current–voltage (polar-
ization) curves were performed by means of an electrochemical
®
analyzer (PGSTAT30, AutoLab , The Netherlands). The polarization
◦
curves were measured in potentiodynamic mode between −20 and
surfaces of the fabricated NiO-SEs after sintering at (a) 800 C, (b)

V.V. Plashnitsa et al. / Electrochimica Acta 55 (2010) 6941–6945
6943
◦
Fig. 3. Cross sensitivities to various gases (400 ppm each) at 800 C under the wet
◦
condition (5 vol.% water vapor) for the YSZ-based sensor using each of the (a) 800 C-,
◦ ◦
b) 1100 C- and (c) 1400 C-sintered NiO-SEs.
(
ing point of nano-structured NiO with an average crystallite size of
◦
◦
3
nm seems to be around 1400 C, which is approximately 600 C
lower than that of the conventional bulk NiO powder. The same
phenomenon of the melting point dependence on crystallite size
was previously observed for nano-structured noble metals, such
as gold [36]. Detailed TEM observations reported by our group
[
32] have revealed that there is no interaction between the NiO
◦
powder and YSZ plate even after sintering at 1400 C. Similarly,
in the present case, the interface between the nano-structured
NiO-SE and YSZ is assumed to be chemically stable and com-
posed of NiO and YSZ without the formation of any secondary
phases.
◦
◦
Fig. 2. Representative SEM images for the surfaces of (a) 800 C-, (b) 1100 C- and
(
◦
c) 1400 C-sintered NiO-SEs fabricated utilizing the nano-structured NiO precursor
obtained at room temperature.
A YSZ-based sensor coupled with a screen-printed NiO-SE has
been recently reported to exhibit good NO -sensing characteris-
2
◦
tics at an operating temperature of 800 C [31,32]. Therefore, the
◦
◦
1
100 C and (c) 1400 C for 2 h. It is clearly seen that both NiO-
present study also focused on the evaluation of gas-sensing perfor-
◦
◦
◦
SEs sintered at 800 C and 1100 C are composed of well-defined
nano-sized NiO grains, although the NiO-SE sintered at 1100 C
mance at 800 C. Fig. 3 shows the cross sensitivities to various gases
◦
◦
at 800 C under the wet condition for the sensors using NiO-SEs
has a more porous structure. Surprisingly, the NiO-SE sintered at
fabricated from the nano-structured precursor and sintered at (a)
◦
◦
◦
◦
1
400 C was found to be partially melted (Fig. 2(c)), which resulted
800 C, (b) 1100 C and (c) 1400 C. It is seen that all of the examined
YSZ-based sensors attached with the NiO-SEs exhibited relatively
high NO2 sensitivity; however, the results for selectivity against
in recrystallization and the formation of a dense NiO layer with
large open pores. Because bulk NiO normally melts at approx-
◦
imately 1980 C, the melting point for the nano-structured NiO
NO2 varied to a large extent. Although the sensor using the less-
◦
seems to strongly depend on the dimensions of the crystallites
that are initially obtained. Thus, based on these results, the melt-
porous 800 C-sintered NiO-SE gave the highest NO sensitivity, the
2
response to NO2 was not selective enough for a possible practical

6
944
V.V. Plashnitsa et al. / Electrochimica Acta 55 (2010) 6941–6945
Fig. 5. Dependence of the NO2 sensitivity on gas concentration in the range of
◦
Fig. 4. Modified polarization curves recorded both in 5 vol.% O2 and in 400 ppm NO2
50–400 ppm NO2 for the sensor attached with 1100 C-sintered NiO-SE operated
at 800 C under the wet condition.
◦
◦
◦
at 800 C in the presence of 5 vol.% H2O for the sensor attached with each of 800 C-,
◦ ◦
100 C, and 1400 C-sintered NiO-SEs.
1
attaining high sensitivity and selectivity to NO , this sensor was
2
application (Fig. 3(a)). The high sensitivity to NO was accompanied
further examined in details. The dependence of NO2 sensitivity on
2
by a relatively large response to CH . The NO selectivity of the pro-
the logarithm of the NO concentration in the range of 50–400 ppm
4
2
2
posed sensor was achieved by increasing the sintering temperature
of the NiO-SE to 1100 C (Fig. 3(b)) despite the slightly lower NO2
clearly shows excellent linearity with a coefficient of determination
(R ) of 0.994. Such excellent linearity is typical for mixed-potential-
◦
2
sensitivity observed. The sensor attached with the partially melted
and dense 1400 C-sintered NiO-SE exhibited high sensitivity to all
of the gases examined (Fig. 3(c)).
type sensors [12].
Fig. 6 depicts the response transients to the different NO2 con-
centrations (50–400 ppm) at 800 C for the sensor coupled with
◦
◦
As has been previously reported [9,12,32], the YSZ-based sen-
sor attached with NiO-SE operated under the mixed-potential
mechanism, in which high NO2 sensitivity arises due to two elec-
trochemical reactions:
the NiO-SE fabricated using the nano-sized precursor and followed
by sintering at 1100 C (Sensor 1, solid line). It should be pointed
◦
out that the NiO-SE used in Sensor 1 was fabricated using a freshly
obtained ball-milled NiO precursor. The emf value was almost equal
to zero under exposure to the base gas and then changed rapidly
from the base level to steady-state values upon switching from the
base gas to the sample gas containing the different NO2 concen-
trations. The response to the same NO2 concentration (400 ppm)
was repeatable. More importantly, even though our gas-flow eval-
uation system was not optimized to obtain the fastest response and
had a large dead volume, the 90% response and 90% recovery times
for the present sensor were estimated to be about 60 and 120 s,
respectively.
the anodic reaction of oxygen : O2 → ½O + 2e−
−
(1)
2
and
the cathodic reaction of NO2: NO + 2e− → NO + O2−
,
(2)
2
which compete at the NiO-SE/YSZ interface. Therefore, the mech-
anism of the present sensors is also believed to be based on
the mixed-potential model. To rationalize that, the measurements
of polarization (current–voltage) curves were performed in the
The utilization of a highly uniform and homogeneous nano-
structured NiO powdered precursor would likely improve the
reproducibility of the NO2 gas-sensing characteristics. To confirm
base gas (5 vol.% O + N2 balance) and in the sample gas (400 ppm
2
◦
NO + 5 vol.% O + N balance) at 800 C under the wet condition for
2
2
2
◦
◦
◦
the sensors attached with each of 800 C-, 1100 C- and 1400 C-
sintered NiO-SEs. The obtained original anodic and the modified
cathodic polarization curves are shown in Fig. 4. For the modi-
fied cathodic polarization curves, the absolute current values for
the difference between currents for the polarization curves mea-
sured in the base gas and in the sample gas were taken. Moreover,
it should be noted that, in the case of a planar sensor operated
◦
this assumption, another sensor attached with 1100 C-sintered
NiO-SE was fabricated and examined (Sensor 2). Sensor 2 was con-
structed about six months later after the examination of Sensor 1.
Importantly, Sensor 2 was fabricated using the same as-received
◦
at 800 C, the Pt-RE is considered as a pseudo air-RE that gives
no mixed-potential and has very high catalytic activities for both
electrochemical reactions (1) and (2). Thus, the anodic reaction of
O2 (1) and the cathodic reaction of NO2 (2) at the interface of the
NiO-SE/YSZ are responsible for establishing the mixed-potential.
As seen in Fig. 4, there is a clear evolution in the catalytic activity
for both electrochemical reactions (1) and (2) which increased with
the decreasing sintering temperature of the NiO-SEs. This results in
nearly invariant intersecting-potential values, which were found
to be very similar to those obtained by the potentiometric mea-
surements (Fig. 3). Such a close agreement between the potential
values confirms that the present sensors are operating under the
mixed-potential mechanism.
◦
Fig. 6. Response transients to NO2 at 800 C in the presence of 5 vol.% water vapor
The dependence of NO2 sensitivity on gas concentration at
for YSZ-based planar sensors attached with each of NiO-SEs fabricated using a com-
mercial powder and the nano-sized ball-milled precursor. (Sensor 1 was constructed
using the freshly obtained ball-milled NiO precursor. Sensor 2 was constructed using
the same as-received amorphous NiO precursor which was stored for about six
months under ambient conditions prior to calcination.) All NiO-SEs studied were
◦
◦
8
(
00 C for the sensor attached with 1100 C-sintered NiO-SE
shown in Fig. 5) demonstrates additional confirmation of the
mixed-potential nature for the present sensor. Because the sinter-
◦
ing temperature of 1100 C was found to be the most relevant for
◦
sintered at 1100 C for 2 h.

V.V. Plashnitsa et al. / Electrochimica Acta 55 (2010) 6941–6945
6945
amorphous NiO precursor, which was stored for about six months
under ambient conditions (room temperature, about 50% relative
The results of reproducibility tests and a comparison of the
fabricated sensor with one using an NiO-SE fabricated from
the commercially available powder revealed the advantages
of mechanochemical pretreatment. Two sensors attached with
◦
humidity) prior to calcination at 1100 C. The response transients to
◦
NO2 at 800 C under the wet condition for Sensor 2 are also shown
◦
in Fig. 6 (dashed-dotted line). It is seen that both sensors were
observed to exhibit reproducible behavior. The difference between
NO2 sensitivities in the range of 100–400 ppm NO2 was found to
be less than 10%. The slight decrease of NO2 sensitivity for Sen-
sor 2 could be attributed to the partial agglomeration of highly
reactive NiO nano-particles during the storage of the precursor
under ambient conditions for the specified period. Nevertheless,
the obtained results are valuable and indicate the utility of the
ball-milling approach in improving the reproducibility of the gas-
sensing characteristics of YSZ-based sensors. More importantly,
good reproducibility of the obtained results for Sensors 1 and 2
is consistent with a reproducible morphology for the fabricated
NiO-SEs as a whole and the stability of the constructed NiO-SE/YSZ
interfaces in particular. This stability could be ascribed to the rela-
tionship between the sintering and melting temperatures for the
nano-structured NiO. Provided that, in the present case, the melting
1100 C-sintered NiO-SEs fabricated within 6 months using the
same mechanochemically obtained NiO precursor showed almost
the same level of NO2 sensitivity even at high operating tempera-
◦
ture. Provided that all kinetic processes are fast enough at 800 C,
the good reproducibility of the NO -sensing characteristics seems
2
to be due to similar catalytic activities for both the anodic and
cathodic electrochemical reactions. Thus, good repeatability of the
electrochemical properties might be attributed to the construc-
tion of morphologically repeatable and stable NiO-SEs as a result
of applying a highly homogeneous nano-structured NiO precursor
and of the proximity between the sintering and melting tempera-
tures.
Acknowledgement
This work was partially supported by the Kyushu University
Global-COE Program on “Novel Carbon Resource Sciences”.
◦
point of the nano-NiO is close to 1400 C, the sintering temperature
◦
of 1100 C is slightly lower than the melting point. Thus, the prox-
imity of the sintering and melting temperatures seems to bring
about the formation of stable and morphologically repeatable NiO
layers.
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6
[
[
NO → NO + ½O .
(3)
2
2
(
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(
◦
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23] K.I. Shimizu, K. Kashiwagi, H. Nishiyama, S. Kakimoto, S. Sugaya, H. Yokoi, A.
Satsuma, Sens. Actuators B: Chem. 130 (2008) 707.
4
. Conclusions
A highly purified, homogeneous and uniform nano-structured
24] V.V. Plashnitsa, P. Elumalai, N. Miura, J. Electrochem. Soc. 155 (2008) J301.
NiO precursor with a crystallite size of about 3 nm was obtained
by ball-milling treatment of parent Ni(OH)2 at room temperature.
The obtained nano-structured NiO powder was utilized for the fab-
rication of NiO-SEs used in a YSZ-based planar NO2 sensor. The
empirical exploration revealed that the melting point of nano-
structured NiO powder was found to be approximately 1400 C,
much lower than the melting point of 1980 C for the conventional
bulk powder. This difference in melting points affected the NO2
gas-sensing characteristics of the NiO-SEs. Even though all of the
[25] J. Yoo, D. Oh, E.D. Wachsman, Solid State Ionics 179 (2008) 2090.
[
26] J. Park, B.Y. Yoon, C.O. Park, W.J. Lee, C.B. Lee, Sens. Actuators B: Chem. 135
2009) 516.
27] L.Y. Woo, R.S. Glass, R.F. Novak, J.H. Visser, J. Electrochem. Soc. 157 (2010) J81.
(
[
[28] J.C. Yang, P.K. Dutta, Sens. Actuators B: Chem. 143 (2010) 459.
[
29] P.K. Sekhar, E.L. Brosha, R. Mukundan, W. Li, M.A. Nelson, P. Palanisamy, F.H.
Garzon, Sens. Actuators B: Chem. 144 (2010) 112.
30] T. Ueda, T. Nagano, H. Okawa, S. Takahashi, J. Ceram. Soc. Jpn. 118 (2010) 180.
◦
[
◦
[31] N. Miura, J. Wang, M. Nakatou, P. Elumalai, M. Hasei, Electrochem. Solid-State
Lett. 8 (2005) H9.
[
32] P. Elumalai, J. Wang, S. Zhuiykov, D. Terada, M. Hasei, N. Miura, J. Electrochem.
Soc. 152 (2005) H95.
◦
fabricated sensors showed high NO sensitivity at 800 C under the
wet condition and the NO2 sensitivity was hardly affected by the
sintering temperature of the NiO-SE, the selectivity against NO2
2
[33] V.V. Plashnitsa, T. Ueda, N. Miura, Int. J. Appl. Ceram. Technol. 3 (2006) 127.
[34] P. Elumalai, V.V. Plashnitsa, Y. Fujio, N. Miura, J. Electrochem. Soc. 156 (2009)
J288.
[
[
35] Y. Fujio, V.V. Plashnitsa, N. Miura, J. Ceram. Soc. Jpn. 118 (2010) 197.
36] P. Buffat, J.P. Borel, Phys. Rev. A 13 (1976) 2287.
◦
was only attained for the sensor attached with 1100 C-sintered
NiO-SE.