Microstructural and chemical evolution near anode triple phase boundary in Ni/YSZ solid oxide fuel cells

In this study, we report the micro-structural and chemical evolution of anode grain boundaries and triple phase boundary (TPB) junctions of Ni/YSZ anode supported solid oxide fuel cells. A NiO phase was found to develop along the Ni/YSZ interfaces extending to TPBs in the operated cells. The thickness of the NiO ribbon phase remains constant at ~ 5 nm in hydrogen for operating durations up to 540 h. When operating on synthesis gas, an increase in interphase thickness was observed from ~ 11 nm for 24 h of operation to ~ 51 nm for 550 h of operation. YSZ phases are observed to be stable in H2 over 540 h of operation. However, for the cell operated in syngas for 550 h, a 5–10 nm tetragonal YSZ (t-YSZ) interfacial layer was identified that originated from the Ni/YSZ interfaces. Yttrium species seem to segregate to the interfaces during operation, leading to the formation of t-YSZ in the Y-depleted regions.

► NiO is observed at Ni/YSZ grain boundaries in cells after electrochemical operation.
► A separate ~10 nm tetragonal YSZ region is observed near at Ni/YSZ interfaces.
► NiO may always be present under operation, but intensifies under syngas exposure.
► Tetragonal-YSZ ribbon phase may be a kinetically limited phenomenon.