Smältkarbonatbränslecellen (MCFC) är en högtemperaturbränslecell för stationära applikationer. Den har samma höga totalverkningsgrad som konventionella kraftvärme-anläggningar, men kan byggas i mindre moduler (från 250 kWe). De små modulerna och den bränsleflexibilitet (naturgas, biogas, etanol, diesel) som MCFC har, gör den intressant för exempelvis industrier med organiska restprodukter och höga krav på tillförlitlighet. Den höga temperaturen och närvaron av en saltsmälta gör dock materialdegradering till en viktig faktor för forskning och utveckling inom området. För även om de fälttester som nyligen gjorts har visat på att vissa av degraderingsprocesserna är mindre allvarliga än förväntat, finns fortfarande ett behov av utveckling för att sänka kostnaderna och förlänga livstiden. I första delen av detta arbete undersöktes material för olika delar av cellen inom ramarna för EU-projektet IRMATECH. Materialen ansågs vara interessanta alternativ till de nuvarande materialen på grund av deras lägre kostnad och/eller bättre prestanda. Två alternativa anodströmtilledarmaterial undersöktes. För anodströmtilledaren är korrosionen och den elektriska resistansen av det eventuella oxidlagret nyckelparametrar. Dessa parametrar undersöktes och utvärderades. Fastän de båda alternativa materialen hade oxidlager med låg resistans, fanns indikationer på korrosionsprocesser som kan äventyra materialets långtidsstabilitet. För katodmaterialet, NiO, har upplösningen varit problemet. De upplösta nickeljonerna fälls ut i elektrolyten och bildar dendriter som kan kortsluta cellen. Därför undersöktes nickelupplösningen hos tre alternativa katodmaterial. Det mest lovande materialet, en nickeloxid-katod dopad med magnesium och järn testades i en singelcell för att studera elektrokemisk prestanda, morfologi och områden där nickelutfällning skett. Resultaten visade att prestandan var jämförbar med NiO, men att den mekaniska stabiliteten måste undersökas ytterligare. I ”wet-seal”-området är det rostfria stålet belagt med ett aluminiumskikt för att skydda det från den mycket korrosiva miljön. Tillverkningsprocesserna för dessa aluminiumbeläggningar har hittills varit dyra och komplexa. Därför utvärderades en alternativ tillverkningsprocess. Beläggningen, studerad i både reducerande och oxiderande miljö visade en tendens till att spricka och därmed exponera det underliggande rostfria stålet. Detta berodde troligtvis på en manuell beläggningsprocess som resulterade i ett inhomogent ytskikt. I den andra delen av arbetet föreslogs en alternativ tillverkningsmetod, baserad på nyligen publicerade resultat där man elektrodeponerat aluminium från jonvätskor. Dessa har ett större katodiskt fönster än vatten och möjliggör därför elektrodeponering av elektropositiva material. För att göra processen industrivänlig provades ett alternativ till den vanligen använda aluminiumtrikloriden. Det visade sig dock att påverkan av miljön på stabiliteten hos jonvätskan behövde undersökas innan några material kunde tillverkas. Vatten i kombination med syre visade sig ha en stor inverkan på den katodiska strömtätheten. I frånvaro av dessa komponenter var jonvätskan mycket stabil. / The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell for stationary applications. It has the same high over-all efficiency (90%) as traditional combined heat and power plants, but MCFC can be built in small modules (from 250 kWe). The small modules in combination with fuel flexibility (natural gas, biogas, ethanol, diesel) makes MCFC an interesting alternative for industries with organic waste and high demands for reliability. The high temperature (650 °C) and the presence of molten salt result however in material degradation. Corrosion and dissolution of the materials used have been the challenge for MCFC. Although long-term field trials have shown that some of the material problems are not as severe as first believed, further material development is necessary to decrease the cost and prolong the life-time. In the first part of this work, materials for different parts of the cell were tested within the EU project IRMATECH. The materials were interesting alternatives to the state-of-the-art materials due to their lower cost and/or better performance. Two alternative anode current collector materials were tested. For the anode current collector the corrosion and electrical resistance of the possible oxide layer are key parameters. These parameters were investigated and evaluated. Although both the materials showed a low resistance, there were indications of corrosion processes which could affect the life-time of the material. For the cathode material, NiO, the dissolution of the material has been a problem. The dissolved nickel ions precipitate in the electrolyte and form conductive nickel dendrites that eventually short-circuit the cell. Therefore, the nickel dissolution of three alternative cathode materials was tested. The most promising material, a NiO doped with magnesium and iron, was tested in a single cell to study the electrical performance, the morphology after operation and the area where nickel had precipitated. The results showed that the performance was comparable to NiO, but it is necessary to investigate the mechanical strength of the material further. In the wet-seal area, the stainless steel is coated with an aluminium coating to protect the material from a severe corrosion environment. The production of aluminium coatings has so far been expensive and complex and an alternative coating process was evaluated. The alternative coating, tested in both reducing and oxidising environments showed a tendency to crack and expose the stainless steel to the corrosive environment. This was suggested being due to the manual coating process that resulted in inhomogeneous coatings. In the second part, an alternative process to coat the wet-seal was suggested, based on recently published results where aluminium had been electrodeposited from ionic liquids. These solvents have a wider electrochemical window than water, and electropositive materials can therefore be deposited. To make the coating process suitable for industrial applications, an alternative to the commonly used AlCl3 was tested. It was shown however, that the influence of the environment had to be investigated before any materials could be produced. The environment, especially water in combination with oxygen was shown to influence the cathodic current density. In absence of these components, the ionic liquid was shown to be very stable. / QC 20100906

<p>Fuel cells are promising candidates for converting chemical energy into electrical energy. The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell that produces electrical energy from a variety of fuels containing hydrogen, hydrocarbons and carbon monoxide. Since the waste heat has a high temperature it can also be used leading to a high overall efficiency.</p><p>Material degradation and the cost of the components are the problems for the commercialisation of MCFC. Although there are companies around the world starting to commercialise MCFC some further cost reduction is needed before MCFC can be fully introduced at the market.</p><p>In this work, alternative materials for three different components of MCFC have been investigated. The alternative materials should have a lower cost compared to the state-of-the-art materials but also meet the life-time goal of MCFC, which is around 5 years. The nickel dissolution of the cathode is a problem and a cathode with lower solubility is needed. The dissolution of nickel for three alternative cathode materials was investigated, where one of the materials had a lower solubility than the state-of-the-art nickel oxide. This material was also tested in a cell and the electrochemical performance was found to be comparable with nickel oxide and is an interesting candidate.</p><p>An inexpensive anode current collector material is also desired. For the anode current collector, the contact resistance should be low and it should have good corrosion properties. The two alternative materials tested had low contact resistance, but some chromium enrichment was seen at the grain boundaries. This can lead to a decreased mechanical stability of the material. In the wet-seal area, the stainless steel used as bipolar/separator plate should be coated. An alternative process to coat the stainless steel, that is less expensive, was evaluated. This process can be a suitable process, but today, when the coating process is done manually there seems to be a problem with the adherence.</p><p>This work has been a part of the IRMATECH project, which was financed by the European Commission, where the partners have been universities, research institutes and companies around Europe.</p>

Fuel cells are promising candidates for converting chemical energy into electrical energy. The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell that produces electrical energy from a variety of fuels containing hydrogen, hydrocarbons and carbon monoxide. Since the waste heat has a high temperature it can also be used leading to a high overall efficiency. Material degradation and the cost of the components are the problems for the commercialisation of MCFC. Although there are companies around the world starting to commercialise MCFC some further cost reduction is needed before MCFC can be fully introduced at the market. In this work, alternative materials for three different components of MCFC have been investigated. The alternative materials should have a lower cost compared to the state-of-the-art materials but also meet the life-time goal of MCFC, which is around 5 years. The nickel dissolution of the cathode is a problem and a cathode with lower solubility is needed. The dissolution of nickel for three alternative cathode materials was investigated, where one of the materials had a lower solubility than the state-of-the-art nickel oxide. This material was also tested in a cell and the electrochemical performance was found to be comparable with nickel oxide and is an interesting candidate. An inexpensive anode current collector material is also desired. For the anode current collector, the contact resistance should be low and it should have good corrosion properties. The two alternative materials tested had low contact resistance, but some chromium enrichment was seen at the grain boundaries. This can lead to a decreased mechanical stability of the material. In the wet-seal area, the stainless steel used as bipolar/separator plate should be coated. An alternative process to coat the stainless steel, that is less expensive, was evaluated. This process can be a suitable process, but today, when the coating process is done manually there seems to be a problem with the adherence. This work has been a part of the IRMATECH project, which was financed by the European Commission, where the partners have been universities, research institutes and companies around Europe. / QC 20101123