Ni-8YSZ cermet re-oxidation of anode supported solid oxide fuel cell: From kinetics measurements to mechanical damage prediction

摘要

The 'redox' tolerance of a typical anode supported cell was evaluated for three temperatures of re-oxidation. For this purpose, an experimental work has been coupled to a modelling approach to estimate the risk of electrolyte failure during re-oxidation. A special attention has been paid to take into account both (i) the heterogeneity of oxidation and (ii) the cermet visco-plasticity in operation. Data required for the simulations - i.e. the oxidation kinetics rates, the cermet expansions and Young's modulus - were determined at T = 600, 700 and 800 ℃. It has been found that the activation energy related to the kinetics of re-oxidation encounters a modification at high temperature (700-750 ℃). This modification has been ascribed to a transition from a homogeneous oxidation process to a heterogeneous one. Local X-ray measurements have confirmed that an oxidation gradient in the cermet arises at T=800℃.Mechanical analysis has shown that the presence of an oxidised front at T = 800℃ strongly impacts the cell 'redox' tolerance. Indeed, this phenomenon induces a significant cell bending, which adds a compressive stress component to the thin electrolyte. Simulations have been carried out to determine both critical degree of oxidation and durations before electrolyte cracking. The effect of the cermet creep during operation on the cell 'redox' tolerance is also discussed.