Mixed ionic-electronic conductivity, phase stability and electrochemical activity of Gd-substituted La2NiO4+δ as oxygen electrode material for solid oxide fuel/electrolysis cells.

Ruddlesden-Popper La 2- x Gd x NiO 4+δ (x = 0–0.4) nickelates were synthesized by glycerol-nitrate combustion technique and explored as potential oxygen electrode materials for solid oxide fuel/electrolysis cells. Similar to the parent La 2 NiO 4+δ , the metastability of RP-type n = 1 structure limits the applicability of La 2- x Gd x NiO 4+δ to temperatures below 900 °C. These solid solutions are mixed conductors with predominantly p -type electronic conductivity that exceeds 50 S/cm at 500–800 °C in air. Substitution by gadolinium does not change the overstoichiometric oxygen content in air but has a negative impact on the mobility of interstitial oxygen, most likely, due to steric effects associated with the lattice shrinkage on doping. The electrochemical activity of bilayer electrodes comprising functional La 2- x Gd x NiO 4+δ and current collecting LaNi 0.6 Fe 0.4 O 3-δ + 3 wt% CuO layers in contact with Ce 0.8 Gd 0.2 O 1.9 electrolyte was studied in air at 550–850 °C. Analysis of electrochemical impedance spectroscopy data employing the ALS (Adler-Lane-Steele) model revealed the limiting role of oxygen-ionic conductivity of functional La 2- x Gd x NiO 4+δ materials in overall electrode performance. • La 2- x Gd x NiO 4+δ (x = 0–0.4) were synthesized by the glycerol-nitrate combustion method. • Gd substitutions do not change oxygen nonstoichiometry in air. • p -type electronic conductivity is above 50 S/cm in air at 500–800 °C. • Crystal lattice shrinkage on substitution has a negative effect on oxygen-ion mobility. • Electrochemical activity of La 2- x Gd x NiO 4+δ electrodes correlates with ionic conductivity. [ABSTRACT FROM AUTHOR]