Ceramic fuel-cells are part of the sustainable energy system in future
Master of science in engineering and VTT’s researcher Mikko Pihlatie has improved new architecture of fuel-cells. Pihlatie presents his thesis about ceramic fuel-cells development in Aalto University School of Science and Technology in 11.6.2010 at 12.00.
An operating Ni-based SOFC can be severely damaged by inadvertent oxidation of
the nickel. A central way to improve this Achilles’ heel is to design and
prepare a dimensionally stable anode half cell that does not overload the
electrolyte upon re-oxidation. Understanding the mechanisms that lead to the
redox expansion, and designing and manufacturing modified anode support
structures that improve stability is the core of the present work.
The behaviour of Ni–YSZ cermets for SOFCs are characterised under conditions cyclically altered between reducing and oxidising (redox cycling). The main operating conditions that affect redox stability are shown to be temperature and humidity; both affect the growth of Ni particles through sintering. The temperature of re-oxidation also plays a significant role in redox stability; a reoxidation at a high temperature (850°C or higher) leads to larger expansions.
The behaviour of the cermet under redox conditions is highly dependent on microstructure; as porosity of the composite increases, redox stability is improved. A redox cycle at 600°C speeds up the subsequent re-reduction significantly, indicating a change in microstructure due to the re-oxidation; also the electrical conductivity of the cermets improves on such a redox cycle. The redox strains during redox cycles below 700°C are reversible, while cumulating strain and damage is created in the ceramic backbone at elevated temperatures.
NiO particle growth during oxidation, combined with low temperature pseudoplasticity is suggested to be a decisive internal factor for redox stability. Redox cycling at high temperatures rapidly leads to irreversible nonelastic strains (cracking, creep) in the YSZ backbone that cause mechanical degradation.
The combination of mild operating conditions and redox-improved cells appears to be a plausible solution to circumvent redox failures. An intentional lowtemperature redox treatment could lead to an improvement in performance. The durability and stability of the anode can be improved by modifications in the microstructure and the composition of the cermets.
Thesis in internet:
Stability of Ni–YSZ composites for solid oxide fuel cells during reduction and re-oxidation
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