Mitigating Ni migration in solid oxide electrolysis by altering Ni-YSZ electrode composition

Abstract

Nickel migration in nickel-yttria stabilized zirconia (Ni-YSZ) fuel electrodes is a significant degradation mechanism limiting the lifetime of solid oxide electrolysis cells, but the factors that control Ni migration are not well understood. Here, we demonstrate that the Ni/YSZ ratio plays an important role in Ni migration. Ni distribution was compared before and after electrolysis operation in 85% H₂O – 15% H₂, 800 °C, −1 A cm⁻² for 500 hours. After testing, clear Ni depletion was observed near the electrolyte in the electrode with an initial 70 wt% NiO content (∼38 vol% Ni, 35 vol% YSZ, 27 vol% pore in the reduced electrode), whereas no Ni depletion was observed in the electrode with an initial 50 wt% NiO content (∼26 vol% Ni, 57 vol% YSZ, 17 vol% pore in the reduced electrode). Two mechanisms are proposed to explain this effect. First, the lower Ni content electrode exhibited ∼45% lower polarization resistance (0.30 vs. 0.54 Ω cm² at 800 °C), reducing the overpotential driving force for migration. Second, 3D microstructural reconstruction revealed that the low-Ni electrode possessed substantially smaller and more isolated surface area per unit volume of Ni-pore interfaces (average z-length 0.97 µm vs. 2.43 µm), which limited the ability of Ni to migrate via surface diffusion across appreciable distances. These findings provide clear design principles for improving SOEC durability through composition optimization.