a b s t r a c tVarious Mn-based oxides have been screened to find a suitable all-solid-state gas-insensitive referenceelectrode (RE) for yttria-stabilized zirconia (YSZ)-based potentiometric oxygen sensor. The experimental observation of tubular YSZ-based sensors attached with each of the outer Mn-based oxide sensing electrodes (SEs) and the inner Pt-RE revealed that Mn 2 O 3 -SE was insensitive to all gases including oxygen at operating temperatures below 550 • C. Thus, the planar-like rod-type YSZ-based sensor using Pt-SE, Au-SE and Mn 2 O 3 -RE was then fabricated and its sensing performances were evaluated at 550 • C. As a result, the planar sensor using a couple of Pt-SE and Mn 2 O 3 -RE exhibited excellent responses to oxygen in the concentration range of 0.05-21 vol.% obeying Nernst equation and gave negligible responses to other co-existing gases. Close similarity of the results for tubular and planar sensors operated in a wide range of air/fuel (A/F) ratio indicated that the tubular YSZ-based sensor using the inner Pt-RE could be successfully miniaturized to the planar one using Mn 2 O 3 -RE without sacrificing its performance.
In an effort to improve propene
(normalC3normalH6)
selectivity and long-term stability of the mixed-potential-type yttria-stabilized zirconia (YSZ)-based tubular sensor attached with
normalIn2normalO3
sensing electrode (SE), each of the nanosized noble metals (Pt, Ru, Pd, Rh, or Ir) and YSZ powder was added to
normalIn2normalO3
SE. It was found that the addition of nanosized Pt
(0.3wt%)
gave considerable improvement in
normalC3normalH6
selectivity, and the addition of YSZ powder
(10wt%)
exhibited great improvement in long-term stability of the sensor. Thus, the sensor attached with composite SE consisting of
normalIn2normalO3
,
0.3wt%
Pt, and
10wt%
YSZ was fabricated and its sensing characteristics to
normalC3normalH6
were examined. As a result, the present sensor exhibited high selectivity and excellent long-term stability to
normalC3normalH6
at
450°C
under the wet condition for the examined period of about
1month
. Based on the results obtained from the measurement of catalytic activity for CO oxidation to
CnormalO2
, the observation of morphology, and the analysis of composition of SEs, it was speculated that the added Pt nanoparticles could promote the oxidation of CO and
H2
and then improve the
normalC3normalH6
selectivity, while the added YSZ powder could stabilize the morphology of the SE∕YSZ interface and give better long-term stability.
Aiming at a sensitive and selective detection of very low concentrations of propene (C 3 H 6) in an atmospheric air, the impedancemetric yttria-stabilized zirconia (YSZ)-based sensor was fabricated and examined. Among the different oxide sensing-electrodes (SEs) studied, SnO 2-SE was found to give the highest sensitivity to C 3 H 6 at 600°C even in the presence of 1.35 vol.% H 2 O and 400 ppm CO 2. Then, the selective response to C 3 H 6 was achieved by coating of the additional oxide layer (ZnO) onto SnO 2-SE, giving the laminated-type ZnO/SnO 2-SE. Moreover, to improve further the sensing performances of the present sensor, ZnO powder (0-30 wt%) was subsequently added to the SnO 2 layer of the laminated ZnO/SnO 2-SE. As a result, the sensor using ZnO/SnO 2 (+20 wt% ZnO)-SE exhibited highly selective and sensitive response to C 3 H 6 at 500 o C with minor cross sensitivities to other co-existing gases, such as NO x , H 2 , CO and CH 4. The sensitivity of the present sensor varied linearly with the logarithm of C 3 H 6 concentration in the range of 20-100 ppb and was found to be hardly affected by the change in water vapor concentration.
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