Abstract
This study explores the impact of A-site deficiency and Sr/Ca ratio on the electrochemical and crystallographic properties of a (Nd(0.2)Sr(0.7-x) Ca (x) ) (y) Ti(0.95)Fe(0.05)O(3-δ) hydrogen electrode for solid oxide cells under reducing and air atmospheres. 5% and 10% A-site deficient (Nd(0.2)Sr(0.7-x) Ca (x) ) (y) Ti(0.95)Fe(0.05)O(3-δ) (x = 0.35-0.45, y = 1.05, 1) (referred to as 5NSCTF-x and 10NSCTF-x) materials were studied, while the ratio between A-site cations was kept the same with both deficiencies. The results demonstrate that the extent of A-site deficiency and the Ca concentration in the A-site have a significant impact on the microstructure (sinterability), conductivity, and catalytic activity of electrodes. Segregation of Nd from the lattice with 5% A-site deficiency was observed as a result of thermal treatment at low pO(2). Among the studied materials, the highest total electrical conductivity of porous electrode layer at 850 °C and in 97% H(2) + 3% H(2)O atmosphere was 4.8 S cm(-1) observed for the Nd(0.2)Sr(0.35)Ca(0.35)Ti(0.95)Fe(0.05)O(3-δ) (10NSCTF-35). The highest electrochemical performance was observed in the case of Nd(0.2)Sr(0.25)Ca(0.45)Ti(0.95)Fe(0.05)O(3-δ) (10NSCTF-45), which showed a polarization resistance value equal to 0.19 Ω cm(2) after 100 h of stabilization at 800 °C in a humidified (1.7% H(2)O) H(2) atmosphere. The best electrochemical performance with 606 mW cm(-2) power density at 850 °C in 98.3% H(2) + 1.7% H(2)O atmosphere was demonstrated by a 50 wt % Nd(0.2)Sr(0.25)Ca(0.45)Ti(0.95)Fe(0.05)O(3-δ) + 50 wt % Ce(0.9)Gd(0.1)O(2-δ) composite.