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» Impedance spectroscopy as a diagnostic tool of degradation of Solid Oxide Fuel Cells
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Konrad Dunst  Sebastian Molin Piotr Jasiński
Solid oxide fuel cell (SOFC) is an electrochemical device that converts
chemical potential energy directly into electrical power. In
comparison with a traditional combustion process, the SOFCs offer
greater efficiency, reliability and environmental friendliness [1].
The SOFCs have a great potential to generate power from a wide
range of fuels: hydrogen, carbon monoxide, hydrocarbons and
alcohols. However, when operated, the fuel cells usually degrade.
The nature of this process depends on the type of the applied
fuel and materials used to fabricate the SOFC. In particular, when
hydrocarbons are used as a fuel, a carbon can deposit inside the
anode structure [2]. The deposited carbon may cause a complete
degradation of the fuel cell.
Further development of the SOFCs requires investigation of
degradation process during fuel cells operation. Among the fuel
cell diagnostic tools, AC impedance spectroscopy is a powerful
technique [3]. This method allows obtaining information about different
electrode processes, namely, oxygen reduction reaction
kinetics, mass transfer and electrolyte resistance losses [4]. Selection
of the appropriate experimental conditions (temperature,
pressure and flow rate) may provide information extracted from
the impedance spectra about the performance losses from the
each fuel cell element separately [3,5].
Different electrode processes reveal unique characteristic
frequencies, which depend on cell structure, materials used for
SOFC fabrication and testing conditions. For example, in case of
the anode supported cells with LSM ((La0.75Sr0.25)0.95 MnO3) cathode
operated at 750°C it was found [6], that the characteristic freque[...]
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ELEKTRONIKA - KONSTRUKCJE, TECHNOLOGIE, ZASTOSOWANIA 2012/1
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» Wytwarzanie i charakteryzacja rezystancyjnych czujników tlenu z wykorzystaniem SrTi0.65Fe0.35O3
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SEBASTIAN MOLIN GRZEGORZ JASIŃSKI MARIA GAZDA PIOTR JASIŃSKI
Czujniki gazów są przyrządami znajdującymi szerokie zastosowanie
w wielu dziedzinach życia. Usprawniają zarówno
liczne procesy produkcyjne, jak i jakość codziennego życia
poprzez kontrolę otaczającej atmosfery. Zastosowanie nowoczesnych
czujników gazów wpływa bezpośrednio na stan środowiska,
czego przykładem są np. czujniki lambda stosowane
w samochodach, które umożliwiają redukcję wydzielania
zanieczyszczeń poprzez kontrolowanie stechiometrycznego
procesu spalania paliwa w silnikach samochodowych.
Wśród dostępnych materiałów, czujniki zbudowane w oparciu
o materiały ceramiczne posiadają wiele wyróżniających je
cech [1]. Są wytrzymałe mechanicznie, pracują w szerokim
zakresie temperatur, mogą być wykonane wieloma technikami:
cienkie/grube warstwy, pastylki, itp.
Wśród kilku typów czujników, wyróżnić można czujniki rezystancyjne,
których zasada działania opiera się na zmianie
przewodności elektrycznej (rezystancji) w wyniku oddziaływania
materiału z którego zbudowany jest czujnik z otaczającymi
gazami. W porównaniu do czujników potencjometrycznych
czy amperometrycznych, budowa czujnika rezystancyjnego
jest mniej skomplikowana. Do prawidłowego działania czujnik
taki nie wymaga ani gazu odniesienia, ani bariery dyfuzyjnej
i może być cały bezpośrednio umieszczony w badanej
atmosferze. Z tego względu, tradycyjną sondę lambda,
wykonywaną najczęściej jako czujnik potencjometryczny
z elektrolitem z YSZ (tlenek cyrkonu stabilizowany tlenkiem
itru - yttria stabilized zirconia) próbuje się zastąpić czujnikami
rezystancyjnymi (np. TiO2, domieszkowane SrTiO3). Czujniki
takie pracują w wysokich temperaturach, powyżej 600°C i muszą
być stabilne w długim okresie działania w agresywnym
środowisku spalin. Podstawową wadą takich materiałów jest
zależność przewodności elektrycznej zarówno od temperatury,
jak i ciśnienia parcjalnego tlenu. Przewodnictwo elektryczne
materiałów ceramicznych stosowanych do konstrukcji rezystancyjnych
czujników tl[...]
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ELEKTRONIKA - KONSTRUKCJE, TECHNOLOGIE, ZASTOSOWANIA 2010/6
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» Electrocatalytic gas sensor with non-triangular excitation
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GRZEGORZ JASIŃSKI ANNA STRZELCZYK BOGDAN CHACHULSKI PIOTR JASIŃSKI
In recent years, solid state ion conducting materials have been
intensively developed. These materials have a relatively high
ionic conductivity based on a single predominantly conducting
anion or cation species and have negligibly small electronic
conductivity. Typically, useful solid electrolytes exhibit ionic
conductivities from 10-1 to 10-5 S/cm at room temperature.
Solid state electrolytes exhibit a potential for application in
a variety of solid state electrochemical devices such as fuel
cells, batteries, membranes, pumps and sensors [1].
Gas sensors are one of the most critical and rapidly growing
areas in modern solid electrolyte technology. Solid state
gas sensors are cost effective, small, rugged and reliable
[2, 3]. Usually electrochemical solid state sensors operate in
either potentiometric or amperometric mode [4, 5]. A lack of selectivity
is sometimes a shortcoming of such sensors. It seems
that improvements of selectivity can be obtained in case of the
electrocatalytic sensors. Their working principle is based on
acquisition of an electric current, while voltage ramp is applied
to the sensor. The current-voltage response depends in a unique
way on the type and concentration of ambient gas.
In case of electrocatalytic gas sensors usually a linearly
changing voltage excitation signal of symmetrical triangular
shape in range from 5 to -5 V is applied to the sensors terminals
[6]. The voltage sweep rate is adjusted to 50 mV/s.
This, originated from liquid electrochemistry, method has
some shortcomings. In typical conditions, one measuring cycle
takes up to 7 min. Stable response is obtained most often
after 2 or more cycles, thus extending measuring time even
further. Long measuring time can limit application of electrocatalytic
sensors in environments with fast gas concentration
changes.
In th[...]
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ELEKTRONIKA - KONSTRUKCJE, TECHNOLOGIE, ZASTOSOWANIA 2011/3
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» Electrocatalytic sensor based on Nasicon with auxiliary layer
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Anna Strzelczyk Grzegorz Jasiński Piotr Jasiński Bogdan Chachulski
In recent years electrochemical gas sensors based on solid state
electrolytes have been intensively investigated. They are relatively
easy to fabricate, simple in use and quite durable. Nasicon
(Na Super Ionic Conductor) is one of the most promising
materials, which have been used in construction of gas sensors.
Sensors based on Nasicon are used for detecting of different
gases including carbon oxides [1, 2], nitrogen oxides [3-6] and
sulfur dioxide [7]. Most of these devices operate in potentiometric
or amperometric mode.
In case of some sensor constructions, besides electrolyte and
metal electrodes, additional layers are applied. In some cases such
phase is required to obtain sensitivity to specific gas or to shift operating
temperature to more preferred one [7]. In other cases sensor
properties such as selectivity or stability are improved. Auxiliary
phase usually forms extra interface between measured gaseous
compound and electrolyte or electrodes. For example, in case of
amperometric sensors, it was noticed, that presence of auxiliary
layer on surface of sensing electrode can increase the number of reaction
sites thus improving sensor sensitivity [5]. Auxiliary layer may
also be used to create a diffusion barrier. In case of the potentiometric
or amperometric nitrogen oxides sensors based[...]
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ELEKTRONIKA - KONSTRUKCJE, TECHNOLOGIE, ZASTOSOWANIA 2012/1
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» Oxide layers fabricated by spray pyrolysis on metallic surfaces
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Katarzyna Kobierowska Magdalena Karpińska Sebastian Molin Piotr Jasiński
A rapid degradation of the implants is the main problem of the
contemporary implantology. Due to the structural role of the bone,
the titanium alloys and austenitic steel, type 316L are frequently
used for the manufacturing of implants. This steel is not deformed,
does not change color, and has hypoallergic properties.
However susceptibility to pitting and crevice corrosion in chloride
ions environment are objectionable features [1].
This is a significant issue to prepare a suitable implant’s outer
layer to improve adhesion of osteogenic cells and anti-corrosion
properties.
The most commonly used methods of thin films layering are:
CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition)
or PLD (Pulsed Laser Deposition). Unfortunately, most of
them are relatively expensive and the process is complex. It would
be useful to find the cheaper method with the less complexity.
Spray pyrolysis deposition of thin ceramic films depends on
the atomization of liquid precursor, droplet transport towards the
heated substrate, droplet impact, spreading the liquid on the substrate
and the evaporation of the solvent, then the distribution of
deposited material [2]. Such layers can be obtained when the
operating temperature is above the boiling point of the precursor.
It is important to remember about the limit of the surface temperature
above which it is not possible to obtain a continuous layers.
In this paper it has been determined the optimal conditions
preparation for the yttrium stabilized zirconium layers on the steel
substrate. The spray pyrolysis method to produce corrosion protective
[...]
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ELEKTRONIKA - KONSTRUKCJE, TECHNOLOGIE, ZASTOSOWANIA 2012/1
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