Achieving thermal cycle stability is an imperative challenge for the successful commercialization of solid oxide cell (SOC) technology. Ruddlesden‒Popper (R‒P) oxides, whose thermal expansion coefficient (TEC) is compatible with common electrolytes, are promising candidates for SOC applications. However, the two-dimensional conduction characteristic of R‒P oxides leads to insufficient catalytic activity, which hinders their performance. Here, we propose a win‒win strategy for self-assembly decoration by employing a one-pot method to address this issue. By using a single perovskite oxide (La_0.4Sr_0.6FeO₃) to modify R‒P oxide (La_0.8Sr_1.2FeO_4+δ), we enhanced the electrochemical performance without compromising the stability of the composite electrode. The strategic incorporation of a 10 mol% perovskite phase at 800 °C resulted in a significant 49% reduction in the polarization resistance (R_p), an impressive 86% increase in the maximum power density under power generation mode, and a notable 33% increase in the electrolysis current density under electrolysis mode. Furthermore, the perovskite-decorated R‒P oxide composite also exhibited high thermal and chemical stability, with negligible performance degradation observed under both thermal cycling and charge/discharge cycling conditions. Our results demonstrate that such dual-phase composites, which are simultaneously produced by a one-step process with outstanding catalytic activity and stability, can be considered an effective strategy for the advancement of SOCs.