Abstract
Metal nanogels combine a large surface area, a high structural stability, and a high catalytic activity toward a variety of chemical reactions. Their performance is underpinned by the atomic-level distribution of their constituents, yet analyzing their subnanoscale structure and composition to guide property optimization remains extremely challenging. Here, we synthesized Pd nanogels using a conventional wet chemistry route, and a near-atomic-scale analysis reveals that impurities from the reactants (Na and K) are integrated into the grain boundaries of the poly crystalline gel, typically loci of high catalytic activity. We demonstrate that the level of impurities is controlled by the reaction condition. Based on ab initio calculations, we provide a detailed mechanism to explain how surface-bound impurities become trapped at grain boundaries that form as the particles coalesce during synthesis, possibly facilitating their decohesion. If controlled, impurity integration into grain boundaries may offer opportunities for designing new nanogels.
Highlights
Despite over 150 years of the “wet” chemical synthesis of colloidal metal nanoparticles and other nanostructures, many aspects of their structure and composition remain elusive, leading to Xia et al saying “an art rather than a science”.1 The wet-synthesis of nanostructures typically involves adding a reducing agent to a solution containing a metal precursor
Nanocrystals form throughout the solution, with their metal−solution interface partly stabilized by impurities, e.g., K and Na
Interfaces become increasingly more stable, but a substantial amount of the large-sized K atoms remain kinetically trapped by the moving surfaces of the growing nanocrystals
Summary
Despite over 150 years of the “wet” chemical synthesis of colloidal metal nanoparticles and other nanostructures, many aspects of their structure and composition remain elusive, leading to Xia et al saying “an art rather than a science”.1 The wet-synthesis of nanostructures typically involves adding a reducing agent to a solution containing a metal precursor. The rapid generation of metal atoms following the introduction of a strong reducing agent results in a high concentration of crystal nuclei, which eventually coalesce into a nanogel and become a metal nanoaerogel (MNA) structure.[6,7] MNAs are an emerging class of self-supported porous materials with potential in electrocatalysis, surpassing commercial metalbased catalysts because of their structural stability and efficient mass and electron transfer channels.[8,9] MNAs have been extensively studied across an array of catalytic applications such as the oxygen reduction reaction,[10,11] the glucose oxidation reaction,[12,13] and the ethanol oxidation reaction.[14,15]. The mechanism we outline will facilitate tailoring MNAs for specific catalytic reactions using insights from atomistic simulations.[20]
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