Rapid and Efficient Exsolution of Nanoparticles in Perovskites Oxides By Atmospheric-Pressure Plasma

Abstract

Exsolved nanoparticles (NPs) in perovskites oxides are highly efficient nano-catalyst in fuel cells or other electrocatalytic applications. Unfortunately, the exsolution process known so far requires energy-intensive processing conditions (for instance, T > 800 oC; treatment duration > 12 h). In this contribution, we report on a fast and efficient way of exsolving NPs by processing a perovskites oxide (La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 2.955, LCTN) in a dielectric barrier discharge (DBD) sustained at atmospheric pressures. Our DBD plasma treatment exsolves NPs within 10-15 minutes in ambient temperature. The exsolution was carried out using a helium DBD with a varying concentration of hydrogen (0-1% H2). The plasma process without hydrogen resulted in the exsolution of Ni NPs from LCTN with an average diameter of around 27 nm and a population density of around 1913 µm-2. The addition of H2 in the helium DBD resulted in an overall decrease in the diameter of the NPs and an increase in their population densities. For instance, the average diameter of the NPs was around 18 nm for both the 0.6% H2 and 1 % H2 while their population densities were found to be increased to around 3347 µm-2 and 4639 µm-2, respectively. Furthermore, NPs sizes down to 5 nm with much higher population densities (> 30k) can be achieved with optimizing plasma and samples geometry conditions. Plasma exsolution is mainly driven by energetic plasma species that are directly in contact with the samples placed in the DBD thereby responsible for densely and well dispersed exsolved NPs, never achieved before even by conventional processes. Surface charging due to plasma electrons is believed as one of the main factors driving exsolution. The role of such electrons is to reduce the metallic ions present on or near the surface. This reduction/exsolution process can further be accelerated by hydrogen-reactive species present in He/H2 DBD. Finally, our plasma exsolution strategy can be further extended to a range of perovskites oxides that would be highly useful in energy devices [1-6].