Ultrafast Flame Exsolution of High-Density Metal Nanoparticles on Perovskite Oxides

Exsolution of metal nanoparticles (NPs) is a powerful strategy for creating strongly attached catalysts for various energy-related applications, but the conventional exsolution methods based on thermal reduction are typically conducted at high temperatures for several hours to achieve sufficient NPs formation. Here, we introduce a new flame exsolution method that is exceptionally simple and rapid for decorating perovskite oxide surfaces with a high density of metal NPs under ambient conditions. By exposing perovskite oxides to a controlled fuel-rich methane-air flame (equivalence ratio, Φ = 1.45), we produced dense Ni NPs (∼500-550 μm^-2) in just 1 min on both (La_0.6Sr_0.4)(Co_0.2Fe_0.8Ni_0.05)O_3-x (LSCF-5Ni) thin films and La_0.43Ca_0.37Ti_0.94Ni_0.06O_3-x (LCTN) pellets. We further demonstrated that similar exsolution results were obtained for both perovskites using a common propane torch within 20 s, demonstrating the method's easy accessibility. This work establishes an ultrafast and transformative pathway to produce high-density metal NPs on perovskite oxides, overcoming the primary limitations of conventional exsolution techniques.