Plasmonic nanoparticles are emerging as a new class of photocatalysts due to their ability to efficiently absorb light and convert it into chemical energy. Compared to traditional semiconducting photocatalysts, plasmonic nanoparticles offer additional routes to improve reactivity, including electromagnetic field enhancement, localized heating and efficient hot carrier excitation. While these effects have been exploited to increase the efficiency of numerous reactions, it remains unclear how the underlying plasmonic excitations affect multi-step reaction kinetics and promote site-selectivity. In particular, most measurements are conducted on particle ensembles, where correlating the reaction dynamics with local structural features is not possible. Single particle measurements help disentangle structure-function relations, but to date only very few such studies exist and all lack the requisite spatial and temporal resolution to directly observe chemical transformations and their associated reaction pathways within a nanoparticle.<br/>Here, we visualize a plasmon-induced phase transformation reaction at the single and sub-nanoparticle level in-situ and in real-time. Using an environmental transmission electron microscope (ETEM) combined with light excitation, we study the photocatalytic dehydrogenation of individual palladium nanocubes coupled to gold nanoparticles; in this configuration, the palladium nanocubes serve as reactors for the dehydrogenation reaction, while the gold nanoparticles serve as efficient visible-light harvesters. A combination of electron diffraction, electron energy loss spectroscopy, and direct imaging provides sub-2nm spatial resolution of the light-induced transformation. We observe two main reaction steps in the dehydrogenation transformation and show that plasmons enhance the reaction rate of these steps in distinct ways, with a more than ten-fold increase in total rate compared to the dark reaction. Additionally, we find that plasmons enable a new phase transformation mechanism that is not observed without illumination. We also show that phase nucleation occurs more often at electromagnetic hot-spots, demonstrating the contribution of plasmons to site-selectivity. The unique capabilities of a combined high resolution TEM and external illumination allow us to study photo-induced reactions in an unprecedented resolution, en-route to design of site-selective and product-specific photocatalysts.

<i>In-situ</i> visualization of plasmon-induced hydrogenation reactions in individual palladium nanocubes

256th National Meeting (2018)

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In-situ visualization of plasmon-induced hydrogenation reactions in individual palladium nanocubes