Activation and failure mechanism of La0.6Sr0.4Co0.2Fe0.8O3−δ air electrode in solid oxide electrolyzer cells under high-current electrolysis

Abstract This work investigates the activation and delamination of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 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.