Cobalt substituted Pr2Ni1-Co O4+ (x = 0, 0.1, 0.2) oxygen electrodes: Impact on electrochemical performance and durability of solid oxide electrolysis cells

This study is focused on the development of layered perovskites based alternative oxygen electrodes for high temperature Solid Oxide Electrolysis Cells (SOECs). In this respect, rare earth nickelates Ln2NiO4+δ (Ln = La, Pr or Nd) have taken considerable attention due to their good electrochemical properties resulting from high oxide ion diffusivity and a large surface exchange rate. Among them, Pr2NiO4+δ (PNO) shows the best electrochemical properties, however, it displays relatively higher degradation rate under SOEC operation at high current density. Therefore, in this work, we perform further modification by substituting nickel by cobalt in order to enhance the physico-chemical properties, electrochemical performance and most importantly the durability of SOECs. Three compositions (x = 0.0, 0.1 and 0.2) are prepared and characterized using different techniques. The electrochemical measurements are performed with symmetrical as well as single cells using DC- and AC-techniques in the 700–900 °C temperature range. The electrode reaction mechanism is also examined by recording the impedance spectra at different pO2. An improvement in electrochemical performance as well as lower degradation rate is observed with cobalt substitution, during short term SOEC operation at −1 A⋅cm−2 current density at 800 °C with 50% H2 and 50% H2O feed gas mixture.