Three dimensional microstructures of carbon deposition on Ni-YSZ anodes under polarization

Abstract

In the present study, two Ni/YSZ anodes with different volume ratios of Ni and YSZ, 30: 70 and 45: 55 vol%, are operated in dry methane under open circuit and polarized conditions. Three-dimensional (3D) Ni/YSZ microstructures after carbon deposition are reconstructed by the focused ion beam-scanning electron microscopy (FIB-SEM) with the help of machine learning segmentation. From the reconstructed mircostructures, volume fraction, connectivity, three phase boundary (TPB) density, and tortuosity are quantified. In addition, local carbon microstructures are quantitatively reconstructed, and the effect of polarization on carbon morphology is investigated. It is demonstrated that Ni surface in the vicinity of active TPB near the electrolyte is free from carbon formation, while remaining Ni surface at some distances from TPB exhibits severe carbon deposition. In average, total amount of carbon deposition is larger near the electrolyte. These observations imply complex interplay between the electrochemical steam generation and methane cracking on Ni surface which take place very locally near the active TPB.