Modelling of the agglomeration of Ni-particles in anodes of solid oxide fuel cells

The degradation of anodes of solid oxide fuel cells (SOFC), which consist of a porous metal − solid electrolyte material is described by a two particle model. The model is based on two main assumptions. Firstly, the difference in metal particle diameter is the driving force for the observed coarsening of the larger metal particle during long term annealing. Secondly, surface diffusion of metal atoms on the particle surface is the dominant diffusion mechanism. Additionally, a function was introduced which considers the limited space for the growth of the nickel particles in the cermet material. The found analytical function for the growth kinetics was compared to experimental results for the growth of nickel particles in a nickel - yttria stabilised zirconia (YSZ) anode annealed at 1000°C up to 4000 h. The model describes the time dependence of the observed particle radii in an adequate way. The resultant surface diffusion coefficients for Ni are lower than results found in literature. Possible explanations are discussed. However, the result shows that the proposed mechanism – surface diffusion of nickel atoms - is fast enough to explain the found amount of Ni agglomeration in SOFC anodes and is therefore considered to be the dominant mechanism.