Microstructure evolution of SOFC pure Ni anode with carbon deposition under polarization

Abstract

In the present study, an electrolyte-supported solid oxide fuel cell (SOFC) is operated in dry methane under different current densities and durations. Pure nickel (Ni) is used for the anode to facilitate the observations of Ni and deposited carbon morphologies. The size of the cathode was made half of that of the anode in order to observe polarized and non-polarized regions of the anode simultaneously. The surfaces and cross sections of the pure Ni anode after carbon deposition were observed by a scanning electron microscopy (SEM) and a laser microscope. The thickness of the carbon layer, the shape of Ni particles, and the density of the triple phase boundary (TPB) were analyzed to investigate the influence of reaction current on carbon deposition. In addition, the study focused the impact of carbon deposition on the morphological changes of Ni particles. It is demonstrated that a high current density could reduce the intensity of carbon deposition in the vicinity of active TPB. High carbon deposition intensity leads to stretching and flattening of Ni particles in different directions, resulting in metal dusting and isolated Ni particles as well as the decrease in TPB. Very high internal stress caused by carbon deposition is considered to be the main reason of Ni morphology change. These observations imply complex interplay between the carbon deposition and Ni morphology change under polarization.