Construction of LaCoO3 with abundant oxygen vacancies and active sites via acid etching–induced surface reconstruction for enhanced catalytic thermal decomposition of ammonium perchlorate

A Novel Acid Etching–Induced Surface Reconstruction Strategy: Unlike conventional approaches that suffer from A-site cation (La 3+ ) surface enrichment, this work introduces a simple HNO 3 etching method to selectively remove surface La 3+ , thereby exposing more Co active sites and generating a LaCoO 3 /Co 3 O 4 heterojunction with significantly increased specific surface area. • Remarkably Enhanced Catalytic Performance for AP Thermal Decomposition: The optimally etched sample (LCO-AC40, etched for 40 min) lowers the high-temperature decomposition peak temperature (T HTD ) of ammonium perchlorate (AP) to 298.1 °C (a decrease of 24.5 °C compared to un-etched LaCoO 3 ), reduces the apparent activation energy from 210.3 kJ·mol −1 to 201.2 kJ·mol −1 . • Synergistic Mechanism of Co 3+ /Co 2+ and Oxygen Vacancies, with Improved Propellant Combustion: The etched surface features coexisting Co 2+ and Co 3+ alongside abundant oxygen vacancies, which collaboratively adsorb initial AP decomposition products and promote redox reactions. Studies have shown that the active sites of synthesized perovskite oxides are generally located at the B-site, but the outermost surface is preferentially occupied by A-site cations (e.g., La 3+ ) rather than B-site cations (e.g., Co 3+ ) which act as the main catalytic active centers, resulting in limited catalytic activity. Therefore, it is necessary to expose more Co sites to enhance the catalytic activity of perovskite oxides. In this work, LaCoO 3 precursors were prepared via the citric acid sol-gel method, and etched with 4% HNO 3 solution for 20, 40 and 60 min respectively to expose more Co active sites. The effects of etching treatment and different etching durations on the catalytic performance for ammonium perchlorate thermal decomposition were systematically investigated. The results demonstrate that the content of surface-exposed Co element can be effectively regulated by adjusting the HNO 3 etching duration. After etching, the Co 3 O 4 phase is generated in the sample and forms a heterojunction with LaCoO 3 , leading to a significant increase in specific surface area. The performance test results show that the un-etched LaCoO 3 reduces the high-temperature decomposition peak temperature ( T HTD ) of AP to 323.0 °C, and the thermal decomposition temperature of the etched samples further decreases. Among them, the sample etched for 40 min (LCO-AC40) has the best performance, reducing the T HTD of AP to 298.1 °C, and the apparent activation energy decreases from 210.3 kJ·mol −1 to 201.2 kJ·mol −1 , while the heat release is significantly increased. The mechanism study indicates that Co 2+ and Co 3+ coexist on the surface of the etched catalytic material, and the increase in Co 2+ content is accompanied by the generation of oxygen vacancies. Co 3+ and oxygen vacancies work together to adsorb the initial decomposition products of AP and promote redox reactions, thereby significantly advancing the thermal decomposition temperature of AP. The combustion test results show that adding LCO-AC40 to the AP/HTPB composite solid propellant makes the flame thicker and brighter, shortens the ignition delay time by 48 ms, and extends the steady-state combustion time. This study provides an effective way to optimize the catalytic performance of perovskite oxides through surface etching strategies and improve the combustion characteristics of composite solid propellants.