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Author:Mikkola, Jyrki
Title:Scaling up MnCo204 Atomic Layer Deposition Process for Fuel Cell Applications
MnCo2O4 atomikerroskasvatus prosessin skaalaaminen suurempaan mittakaavan polttokennosovelluksiin
Publication type:Master's thesis
Publication year:2013
Pages:viii + 83      Language:   eng
Department/School:Kemian laitos
Main subject:Kemia   (KE3001)
Supervisor:Karppinen, Maarit
Instructor:Himanen, Olli
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201402181419
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  1900   | Archive
Keywords:interconnect
protective coating
SOFC
bipolaarilevy
suojapinnoite
MnCo2O4
ALD
Abstract (eng):Solid oxide fuel cells (SOFCs) are an interesting choice for an energy production because of their high efficiency, low emission rate and fuel flexibility.
Metallic interconnect plates, which separate fuel and oxidant from each other, act as electrical and thermal conductors between adjacent cells and give mechanical support to stack structure, suffer from oxidation and degradation at operat-ing temperatures of 600 - 800 °C.
Thus, they need protective coatings which are reviewed in this thesis.

The spinel structured MnCo2O4 has drawn attention recently as a protective material and its preparation by atomic layer deposition (ALD) is studied in the experimental part.
ALD is a chemical vapour deposition technique for manufacturing thin films.
It offers an interesting method for applying protective coatings because the ALD process is precise and repeatable and can be used to manufacture homogenous and dense films.
The aim of this thesis was to scale up the MnCo2O4 ALD process so that 9 x 9 cm2 ferritic stainless steel interconnect plates for solid oxide fuel cells can be coated with 100 nm thick coatings.
Manganese precursor condensation and thus clogging of the precursor line has been a problem in previous studies.
In this work this problem was overcome by installing the additional heating cable to the source line and near the valves in the source system.
The best parameters for an effective film growth were looked for and the deposited films were analysed by X-ray methods and time-of-flight elastic recoil detection analysis.

The most efficient film growth was seen when the deposition temperature was 160 °C and the manganese and cobalt precursor temperatures were 155 and 140 °C respectively.
Then the growth rate of the film was about 0.027 nm/cycle.
It was observed that the desired cation ratio in MnCo2O4 was reached when the Co/Mn pulsing ratio of 3:4 is used.
It was also seen that the efficiency of the ozone generator and thus the efficiency of the deposition increases notably when there is 5 % nitrogen among oxygen in the inlet gas of the generator.

The MnCo2O4 ALD process was successfully scaled up for coating real interconnect plates in a sin-gle wafer reactor.
The process possesses potential to be a cost-effective way to coat solid oxide fuel cell interconnects in industrial process after further scaling up.
Abstract (fin):Kiinteäoksidipolttokennot (Solid oxide fuel cell, SOFC) ovat varteenotettava energiantuotantomenetelmä hyvän hyötysuhteensa, vähäisten päästöjensä ja laajan polttoainevalikoimansa vuoksi.
Bipolaarilevyt toimivat kennostossa sähköjohtimina, polttoaineen ja hapettimen erottimena ja mekaanisena tukena.
Ne kärsivät kuitenkin hapettumisesta ja suorituskyvyn heikkenemisestä 600 - 800 °C:n toimintalämpötilassa.
Tämä vuoksi bipolaarilevyt tulee suojata pinnoitteella, joiden ominaisuuksia on tarkasteltu kirjallisuusosassa.

Spinellirakenteinen MnCo2O4 on osoittautunut lupaavaksi suojapinnoitteeksi.
Kokeellisessa osassa tutkittiin MnCo2O4:n valmistusta atomikerroskasvatusmenetelmällä (Atomic layer deposition, ALD).
ALD on kemiallinen kaasufaasimenetelmä ohutkalvojen valmistamiseksi.
Se on tarkka ja toistettava menetelmä, jonka avulla pystytään valmistamaan tiheitä ja tasaisia pinnoitteita.
Tämän diplomityön tarkoituksena oli skaalata MnCo2O4 ALD prosessi suurempaan mittakaavaan siten, että ruostumattomasta teräksestä valmistettuja biolaarilevyjä voidaan pinnoittaa 9 x 9 cm2 alueelle korkealaatuisella 100 nm paksulla kalvolla polttokennosovelluksia varten.
ALD kasvatuksissa on ollut aiemmin ongelmana mangaanilähtöaineen kondensoituminen, jonka estämiseksi reaktoria muokattiin asentamalla lähteeseen ja lähtöainelinjaan lisälämmitys, jonka avulla kondensoituminen ja linjan tukkeutuminen estettiin.
Ohutkalvon kasvamiselle tehokkaimmat parametrit etsittiin ja kasvatettuja kalvoja analysoitiin röntgenmenetelmillä sekä syvyysprofiilin avulla.

Paras kalvon kasvu saavutettiin, kun kasvatuslämpötila oli 160 °C ja mangaani- ja kobolttilähtöaineiden sublimointilämpötilat olivat 155 ja 140 °C vastaavasti.
Kalvon kasvunopeus oli tällöin 0,027 nm/sykli.
Haluttu kationisuhde MnCo2O4 pinnoitteessa saavutettiin, kun Co/Mn pulssitussuhde pinnoitusprosessissa oli 3:4.
Lisäksi huomattiin, että otsonigeneraattorin toimintatehokkuus kasvaa huomattavasti, kun generaattorille tulevan hapen joukossa on 5 % typpeä.

MnCo2O4 ALD prosessi saatiin skaalattua suurempaan mittakaavaan siten, että bipolaarilevyjä voidaan pinnoittaa yksi kerrallaan.
Prosessilla on potentiaalia teollisesti kannattavaksi menetelmäksi bipolaarilevyjen pinnoittamiseen, kun sitä skaalataan edelleen suurempaan mittakaavaan.
ED:2014-02-19
INSSI record number: 48678
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