Surface modification with nanoparticles has been widely studied to promote catalytic activity and stability of the oxygen electrode in solid oxide electrochemical cells (SOCs). However, attaining uniformity and scalability of the nanoparticles remains a challenging endeavor. Herein, we developed a highly conductive nano-sized Sm3+ and Nd3+ double-doped ceria decorated La0.6Sr0.4Co0.2Fe0.8O3-δ -Gd0.1Ce0.9O2- δ (SNDC@LSCF-GDC) oxygen electrode via an ultrasonic spray infiltration technique. The uniform SNDC infiltrates promote oxygen catalytic activity by increasing oxygen vacancies and reaction sites on the surface of the electrode. The SOC with the SNDC@LSCF-GDC oxygen electrode shows high performance in fuel cell (1.97 W/cm2 at 750 °C) and electrolysis cell (1.72 A/cm2 at 750 °C) modes. Moreover, ultrasonic infiltration-based SNDC nanoparticles were successfully demonstrated in a large-size commercial cell (10 cm × 10 cm effective area), showing increased power output and remarkable stability for 960 h. This work presents a scalable and feasible way to decorate large area electrodes with uniform infiltrates for energy storage and conversion applications.