Mechanical reliability and durability of SOFC stacks. Part II: Modelling of mechanical failures during ageing and cycling

Intricate relationships between mechanical and electrochemical degradation aspects likely affect the durability of solid oxide fuel cell stacks. This study presents a modelling framework that combines thermo-electrochemical models including degradation and a contact thermo-mechanical model that considers rate-independent plasticity and creep of the components materials and the shrinkage of the nickel-based anode during thermal cycling. This Part II investigates separately or together the contributions of mechanical and electrochemical degradation on the behaviour during long-term operation and thermal cycling.Electrochemical degradation modifies the temperature profile under constant system power conditions and consequently the risks of cell failure. Irreversible deformation of the stack components causes losses of contact pressure during thermal cycling and variation of the electrical load and changes the risks of anode and cathode cracking. Critical tensile stress progressively develops in the cell compatibility layer (GDC between YSZ and LSCF) during thermal cycling depending on the temperature profile in operation.

► Analysis of the trade-offs characterizing electrochemical and mechanical durability. ► Combined effects of plastic deformation and temperature profile variations. ► Investigation of the risks of mechanical failures induced by long-term operation. ► Identification of localized losses of electrical contact during long-term operation. ► Simulation of the thermal history-dependent behaviour of SOFC stack.