Investigating exsolution of metal nanoparticles is an area of evolving interest. Metal nanoparticles have been found to exsolve from metal oxides in the perovskite family under reducing conditions and investigated as fuel cell anodes. Professor Stephen Skinner works at the Department of Materials at Imperial College, and today spoke about the research his group has been carrying out on high-performance materials for hydrogen production.
Professor Skinner uses scanning and transmission electron microscopy (SEM and TEM) to characterise the morphology of double perovskites, for example lanthanum nickel ruthenates, and the metal nanoparticles exsolved from them. The exsolved particles are smaller than 20 nm in size and, as they remain partially embedded in the oxide, they show greater stability against sintering than traditional supported nanoparticles. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) have confirmed the exsolution of the metal, and how this varies with temperature in dry and wet atmospheres. The exsolution results in a decreasing electrode resistance, indicating an enhanced electrochemical catalytic activity.
The diffusion profile of isotopically labelled oxygen through the material was probed using time-of-flight secondary ion mass spectrometry (ToF-SIMS). A significant difference in the diffusion rate was observed with oxygen gas and steam; although the diffusivity of the underlying lattice cannot change, the reducing effect of the steam changes the stoichiometry of the material and, hence, the number of defects present. Methods to optimise the structure for solid oxide fuel cell performance were considered, and the variation monitored with the changing double- and triple-phase boundary density. A simple mechanical milling process was seen to be effective, as confirmed by a lower electrode resistance.
Professor Skinner’s research in the area of solid oxide fuel cells and electrolysers includes materials development as well as structural and functional characterisation. His group at Imperial is currently working on oxide ion conducting air electrodes and proton transport in oxides. You can read more about this work here.