Tailoring Oxygen Vacancy Concentration and Triple‐Phase Boundaries in Transition Metal‐Doped La _0.8 Sr _0.2 MnO _{3– <i>δ</i>} Air Electrodes for High‐Performance Solid Oxide Cells

Solid oxide cells (SOCs) have attracted significant attention as promising energy conversion systems due to their reversibility and high efficiency. La 0.8 Sr 0.2 MnO 3– δ (LSM) is a conventionally used air electrode in SOCs but suffers from low electrochemical activity at low operating temperatures, limiting its overall cell performance. This study presents the development of transition metal‐doped LSM perovskite oxides to enhance electrochemical activity. The developed electrodes, sintered at various temperatures, exhibited improved performance in both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This enhancement was primarily attributed to two key factors: the high concentration of oxygen vacancies () and the increased density of triple‐phase boundaries (TPBs). In half‐cell tests, La 0.8 Sr 0.2 Mn 0.8 Co 0.2 O 3– δ (LSMCo)–scandia stabilized zirconia (ScSZ) exhibited an eight‐fold reduction in polarization resistance (0.034 Ω cm 2 versus 0.29 Ω cm 2 for undoped LSM–ScSZ) at 800°C. Furthermore, a single cell with the LSMCo–ScSZ electrode achieved a maximum power density of 0.7 W/cm 2 in fuel cell mode and a current density of 0.8 A/cm 2 in electrolysis cell mode (at 1.3 V) under 50% H 2 O/H 2 fuel conditions at 800°C. These results provide a viable and straightforward strategy for enhancing the electrochemical activity of the air electrodes in diverse and sustainable energy applications.