Electrochemical Model of Solid Oxide Fuel Cell for Simulation at the Stack Scale II: Implementation of Degradation Processes

Abstract

The degradation of the electrochemical performance of solid oxide fuel cell (SOFC) devices is a major hurdle to overcome before commercialisation. The interplay between the phenomena and the long testing times complicate the research, which highlights the relevance of modelling to propose mitigation approaches.This study comprises two parts. This Part II proposes approaches for the simulation of the degradation induced by: (i) interconnect corrosion, (ii) loss of ionic conductivity of the ion-conducting materials, (iii) nickel particle growth in the anode, (iv) chromium contamination and (v) formation of insulating phases in the cathode. The literature survey highlights the lack of data for a completely consistent calibration of the models, despite the simplifications. The support for the implementation is the electrochemical model validated in Part I and a two-dimensional model of the cell and interconnection system. The cathode largely contributes to the degradation. The local overpotential predominantly governs chromium contamination, which can promote the formation of insulating phases, as operation proceeds. The local electronic current density has comparatively a weak direct influence on the degradation. Qualitative agreement with experimental data from the literature could be achieved, without dedicated adjustments of the parameters.

Progressive activation of degradation processes in solid oxide fuel cells stacks: Part I: Lifetime extension by optimisation of the operating conditions

“…The description of the modelling approach, the value of the parameters and the analysis of the local behaviour can be found in Ref. [20]. The selected degradation phenomena are the (i) decrease in ionic conductivity of 8YSZ, (ii) MIC corrosion, (iii) anode nickel particle growth and, (iv) chromium contamination and (v) formation of zirconates in the LSMeYSZ cathode.…”

“…The semi-empirical relation for the evolution of the nickel particle radius depends on temperature, steam and hydrogen partial pressure and tends to a maximum value due to the mechanical constraint imposed by the YSZ network. In the model, the time to reach the plateau value spans from 1000 h to 10,000 h [20] under the local conditions found in an intermediate SOFC stack.…”

“…The temperature-dependent plateau value is reached in the model after 500 he2500 h [20]. The trend in the evolution after ageing during more than 5000 h is not included in the data.…”

“…As discussed in Ref. [20], because the focus of experimental studies is principally on either (i) gaining knowledge on the underlying processes or (ii) scanning for the best technological solution, the range of investigated conditions does usually not cover that found in SOFC stacks in operation. Herein lies their partial incompatibility, in particular that of (ii), with modelling at the SRU/stack scale.…”

“…Our calibrated electrochemical model, which includes several simultaneous degradation phenomena [20,25] is implemented in SRU models of a planar, intermediate-temperature, anode-supported stack design to investigate their combined detrimental effect on the durability under the practical operating conditions an SOFC stack must withstand in the field. The decrease in ionic conductivity of 8YSZ, metallic interconnect (MIC) corrosion, nickel particle growth and chromium contamination of the LSMeYSZ cathode, completed by transport of volatile chromium species [22], are considered.…”