Abstract
An SOFC stack operated for 40,000 hours has been dismantled offering the opportunity to characterize the metallic interconnect. The metal plate was carefully investigated to define the evolution of the surfaces exposed to the air and to the hydrogen electrodes respectively. The observations of the surfaces reveal the stability of the layers applied on top of the rib at the air side while in the bottom of the channels the protective coating (i.e., Co-Mn base spinel oxide) shows large crystals. The cross section allowed to highlight the formation of a rather homogeneous layer of thermal grown oxide between the metal and the coating. The average thickness of the TGO is around 11 μm. The hydrogen side shows a superficial alteration (due to the interaction with the water vapour) changing from the inlet to the outlet where it seems thinner as if the TGO further reacted by forming volatile compounds. The cross section observations confirmed the presence of a porous TGO with a rather high content of manganese in a Cr-Mn spinel oxide. Several spots testifies the zones of contact with the Ni base contacting layer. The cross section corresponding to such zones highlighted the Ni diffusion in the metal substrate.
Highlights
In the perspective of an efficient decarbonisation of the energy production the usage of hydrogen as fuel for power plants seems to be a logical solution [1] due to its compliance with the renewable power sources often characterized by the intermittence of operating period and by the need of an energy storage solution
The MIC was extracted by an solid oxide fuel cells (SOFC) stack manufactured and operated by Sunfire company (Sunfire GmbH, Dresden, Germany) according to the disclosable working conditions listed in table 1
The H2/H2O gradient is constantly evolving from the Inlet zone toward the Outlet zone with an increase of water vapour corresponding to a reduction of the hydrogen partial pressure
Summary
In the perspective of an efficient decarbonisation of the energy production the usage of hydrogen as fuel for power plants seems to be a logical solution [1] due to its compliance with the renewable power sources (e.g., photovoltaic, wind power) often characterized by the intermittence of operating period and by the need of an energy storage solution. The solid oxide fuel cells (SOFC) are favoured for their high efficiency in energy conversion of the reaction between hydrogen and oxygen reaching more than 90% if heat and electrical power are considered [1]. The operating time needed to make the stack built around SOFCs is at least 50,000 hours even though the ideal time would be 80,000 hours at an operating temperature between 650°C and 850°C and an optimal fuel consumption of 80%. The evolution of the components inside a stack is strictly related to the efficiency of the whole system and involves materials evolution and the interaction between materials [2,3,4]
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