Morphology-Dependent Reactivity of a Plasmonic Photocatalyst

The shape of a plasmonic nanoparticle strongly controls its light-matter interaction, which in turn affects how specific morphologies may be used in applications such as sensing, photodetection, and active pixel displays. Here, we show that particle shape also controls plasmonic photocatalytic activity. Three different Al nanocrystal morphologies, octopods, nanocubes, and nanocrystals, all with very similar plasmon resonance frequencies, were used as photocatalysts for the H₂ dissociation reaction. We observe widely varying reaction rates for the three different morphologies. Octopods show a 10 times higher reaction rate than nanocrystals and a 5 times higher rate than nanocubes, with lower apparent activation energies than either nanocubes or nanocrystals by 45% and 49%, respectively. A theoretical model of hot electron direct transfer from photoexcited Al nanoparticles to H₂ molecules is consistent with this observed morphological dependence. This research strongly suggests that nanoparticle geometry, in addition to plasmon resonance energy, is a critical factor in plasmonic photocatalyst design.