The high-temperature carbonate fuel cell is an ultra-clean and high-efficiency power generator. Its intermediate operating temperature, ∼600–650°C, is considered optimum to facilitate fast fuel cell reaction kinetics, utilize waste heat efficiently in a combined heat and power or bottoming power cycle, and at the same time allow use of commercial commodity materials for cell hardware and balance-of-plant (BOP) piping/equipment construction. MW size power plants manufactured by FCE are being operated at customer sites throughout the world. The cell hardware and BOP materials selections are founded on many years of focused research. Microstructure and mechanical property evolution, oxidation, hot corrosion and carburization have been extensively investigated. Long-term subscale stack endurance as well as power plant field operation results to date show that the baseline hardware construction materials meet the endurance goals. Material durability is well understood and solutions are available to further extend life. This paper will review durability experience of hardware materials (cell, stack and BOP).

Currently there are three major liquid-electrolyte fuel cells: alkaline (AFC), phosphoric (PAFC) and carbonate fuel cells, utilizing liquid electrolytes KOH, H3PO4 and M2CO3 (M: alkali ions), respectively. The electrolytes provide ionic conduction, reactant gas separation, and electrochemical kinetics. The electrolyte inventory and distribution in operating fuel-cell electrochemically-active cell components (electrodes and electrolyte matrix) need to be carefully managed to achieve desired performance and life. There are many similarities in physicochemical/electrochemical processes as well as electrolyte management schemes in these fuel cells. Internal-reforming carbonate fuel cell (Direct Fuel Cell, DFC®) is being commercially deployed by FuelCell Energy (FCE), its German subsidiary FCES (FuelCell Energy Solutions), and South Korean partner POSCO Energy. Successful electrolyte management schemes had allowed DFC stacks to achieve commercial stack performance and endurance goals. In this paper, electrolyte processes and management schemes in these three major liquid-electrolyte fuel cells are reviewed.

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The high-temperature carbonate fuel cell is an ultra-clean and high-efficiency power generator. It is operated at ~550-650ºC, an optimum temperature range to facilitate fast fuel-cell reaction kinetics, provide high-quality waste heat, and allow use of commercial available materials. Over eighty power plants manufactured by FCE are operating at customer sites throughout the world. The material selections are founded on many years of focused research. Long-term stack endurance as well as field operation results to date show that the baseline construction materials meet the present 5-year endurance goals. Material durability is well understood and solutions are available to further enhance life and durability.

Because of its size, low emission, high temperature operation and resulting high efficiency, high-temperature fuel cell is ideally suited to commercial, industrial cogeneration and utility distributed generation applications. High-temperature operation facilitates fast fuel cell reaction kinetics and allows practical internal reforming and cogeneration/hybrid applications. Heat-resistant alloys have been extensively used in high-temperature fuel cells. The cell, stack and BOP hardware alloy selections are founded on many years of focused research. Alloy selection needs to take into account corrosion stability, mechanical properties and cost. The field hardware stability data confirms that the material solutions employed are robust to achieve desired long (approaching ten year) carbonate fuel cell service life. Material durability is well understood and solutions are available to further extend life.