Revealing the critical role of point defects in controlling metal nanocatalyst exsolution for clean energy conversion
Nanostructured catalysts are the key enablers in electrochemical energy and fuel conversion. A recent advance in this field is to synthesize oxide-supported metal nanoparticle catalysts via “exsolution”, where metallic nanoparticles are precipitated out of the host oxide upon reduction. Unlike the deposited or infiltrated nanoparticles, the exsolved nanoparticles are anchored in the host oxide, making them more resistant to particle agglomeration. As a result, the exsolved nanoparticles often exhibit outstanding catalytic stability under operating conditions.
While exsolution is powering a revolution in nanoengineering, the underlying reactions controlling it remain poorly understood. In particular, it remains unclear what factors control the size and density of the exsolved nanoparticles. In this presentation, I will discuss the critical role of point defects in dictating both the thermodynamics and kinetics of metal exsolution. First, by quantifying surface chemistry evolution with near-ambient pressure XPS (NAP-XPS), we identified the initial oxygen vacancy formation and the following Schottky defect formation as the primary defect reactions in exsolution. Secondly, with the aid of density functional theory (DFT) and Monte Carlo (MC) calculations, we suggest surface oxygen vacancy clusters to be the nucleation sites for the exsolved particles on single-crystalline oxide surfaces. These findings underscore the critical significance of surface point defects in governing the size and density, and consequently, the catalytic activity of the exsolved nanocatalysts.