Small Change, Big Difference: Photoelectrochemical Behavior of Au Nanocluster-Sensitized TiO₂Altered by Core Restructuring

Ultrasmall gold nanoclusters (Au NCs) have recently gained enormous popularity as a newly emerging light harvester, but many fundamental aspects of their photoelectrochemical behavior are still largely unknown. Unlike traditional photoactive nanoparticles, the NC's core structure, rather than its size, is a key factor that dictates the physical properties of NCs because of a strong quantum confinement effect. Despite this importance, no effort has been made to elucidate the effect of the core structure on the photoelectrochemistry of Au NC-sensitized TiO2 (Au NC-TiO2). Using Au25 NC as a model system, we delicately tailored the icosahedral Au13 core of Au25 NC into a cuboctahedral Au15 core of Au23 NC. This subtle core manipulation has a drastic impact on the entire interfacial behavior of Au NC-TiO2, which in turn significantly affects the photoelectrochemical performance. This new insight highlights the overlooked effect of the core structure on the photoelectrochemistry of Au NC-TiO2.