Thermal stability and coalescence dynamics of exsolved metal nanoparticles at charged perovskite surfaces

Exsolution reactions enable the synthesis of oxide-supported metal nanoparticles, desir- able as catalysts in green energy conversion technologies. It is crucial to precisely tai- lor the nanoparticle characteristics to tune the catalysts’ functionality, and to maintain the catalytic performance under operation conditions. We use chemical (co)-doping to modify the defect chemistry of exsolution-active perovskite oxides and we examine the Ni exsolu- tion behavior at atomically smooth surfaces of p-type SrTi0.95Ni0.05O3−δ (STNi) and n-type SrTi0.9Nb0.05Ni0.05O3−δ (STNNi) with identical (001) surface orientation. We identify dis- tinct differences in the mass transfer kinetics of Ni dopants towards the oxide surface and in the subsequent coalescence behavior of the exsolved nanoparticles at the perovskite surface during a continuous thermal reduction treatment. Nanoparticles that exsolve at the surface of the p-type fast-oxygen-ion-conductor STNi show a high surface mobility and thus a very low thermal stability compared to nanoparticles that exsolve at the surface of n-type STNNi. Our analysis indicates that the low thermal stability of exsolved nanoparticles at the acceptor-doped perovskite surface is associated to a large oxygen vacancy concentration at the nanoparticle-oxide interface, hampering the applicability of the exsolution synthesis route for catalysts that require a fast oxygen exchange kinetics.