Evaluation of oxide ceramics as anodes for SOECs

Abstract

La₂NiO_4+δ is characterised as an example for a potential anode material for high-temperature solid oxide electrolyser cells (SOECs). Short-term characterisation is performed from 700 °C to 850 °C between 0.01 and 1 bar oxygen partial pressure (pO₂) on asymmetrical cells using Ce_0.9Gd_0.1O_2−δ as the electrolyte. Long-term degradation studies over more than 3000 hours are conducted at 800 °C and 0.2 bar pO₂ in dry and humid atmospheres with and without a Cr-source placed in close vicinity to the cell. The SOEC anode performance is investigated by current–voltage curves combined with impedance spectroscopy. Current densities of up to −410 mA cm⁻² are applied in current–voltage measurements and during long-term degradation studies. A total increase in anode resistance by 350% is observed over the course of the degradation measurements in an increasingly harsh environment. Post-test analyses by SEM/EDX on a polished cross section of the cell show the presence of several contaminants in the electrode structure. However, chromium has not been identified by EDX even after prolonged exposure to Cr-sources in humid atmospheres, which is attributed to the anodic polarisation of the electrode. Electrode delamination appears to be the main factor for the strong loss in performance.