Activation and failure mechanism of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−Δair electrode in solid oxide electrolyzer cells under high-current electrolysis

This work investigates the activation and delamination of La _0.6Sr _0.4Co _0.2Fe _0.8O _3−δ (LSCF) air electrode of solid oxide electrolyzer cells sintered on yttria-stabilized zirconia (YSZ) electrolyte. After polarization with an electrolysis current of 1 A cm ⁻² for 24 h at 800 °C, the LSCF electrode delaminates accompanied by an increase of ohmic and polarization resistance. Notably, polarization resistance decreases at the beginning. By scanning electron microscopy (SEM), a thin but dense layer is observed at the LSCF–YSZ interface of an as-prepared sample, which is identified as SrZrO ₃ phase by X-ray diffractometry. This layer causes the initial high polarization resistance due to retarded ionic and electronic conductivity. After the test, SEM reveals that the SrZrO ₃ layer delaminates from YSZ electrolyte. Moreover, energy dispersive X-ray tests confirm that Co diffuses to the SrZrO ₃ layer and SrZrO ₃–YSZ interface. Later, the LSCF electrode with Co-containing SrZrO ₃ layer is shown to perform better than that with pure SrZrO ₃ layer. Thus, Co diffusion can be the reason for the initial decrease of polarization resistance and renders the generation of oxygen at SrZrO ₃–YSZ interface during the electrolysis. Owing to its limited porosity, the SrZrO ₃ layer traps the generated oxygen. High pressure eventually builds up at the SrZrO ₃–YSZ interface driving the delamination of SrZrO ₃ layer, and hence the entire LSCF electrode.