Visible-light-driven photochemistry has continued to attract heightened interest due to its capacity to efficiently harvest solar energy and its potential to solve the global energy crisis. Plasmonic nanostructures boast broadly tunable optical properties coupled with catalytically active surfaces that offer a unique opportunity for solar photochemistry. Resonant optical excitation of surface plasmons produces energetic hot electrons that can be collected to facilitate chemical reactions. This review sums up recent theoretical and experimental approaches for understanding the underlying photophysical processes in hot electron generation and discusses various electron-transfer models on both plasmonic metal nanostructures and plasmonic metal/semiconductor heterostructures. Following that are highlights of recent examples of plasmon-driven hot electron photochemical reactions within the context of both cases. The review concludes with a discussion about the remaining challenges in the field and future opportunities for addressing the low reaction efficiencies in hot-electron-induced photochemistry.

After more than a decade, it is still unknown whether the plasmon-mediated growth of silver nanostructures can be extended to the synthesis of other noble metals, as the molecular mechanisms governing the growth process remain elusive. Herein, we demonstrate the plasmon-driven synthesis of gold nanoprisms and elucidate the details of the photochemical growth mechanism at the single-nanoparticle level. Our investigation reveals that the surfactant polyvinylpyrrolidone preferentially adsorbs along the nanoprism perimeter and serves as a photochemical relay to direct the anisotropic growth of gold nanoprisms. This discovery confers a unique function to polyvinylpyrrolidone that is fundamentally different from its widely accepted role as a crystal-face-blocking ligand. Additionally, we find that nanocrystal twinning exerts a profound influence on the kinetics of this photochemical process by controlling the transport of plasmon-generated hot electrons to polyvinylpyrrolidone. These insights establish a molecular-level description of the underlying mechanisms regulating the plasmon-driven synthesis of gold nanoprisms.

The metal/oxide interface has been extensively studied due to its importance for heterogeneous catalysis. However, the exact role of interfacial atomic structures in governing catalytic processes still remains elusive. Herein, we demonstrate how the manipulation of atomic structures at the Au/TiO 2 interface significantly alters the interfacial electron distribution and prompts O 2 activation. It is discovered that at the defect-free Au/TiO 2 interface electrons transfer from Ti 3+ species into Au nanoparticles (NPs) and further migrate into adsorbed perimeter O 2 molecules (i.e., in the form of Au−O−O−Ti), facilitating O 2 activation and leading to a ca. 34 times higher CO oxidation activity than that on the oxygen vacancy (V o )-rich Au/TiO 2 interface, at which electrons from Ti 3+ species are trapped by interfacial V o on TiO 2 and hardly interact with perimeter O 2 molecules. We further reveal that the calcination releases those trapped electrons from interfacial V o to facilitate O 2 activation. Collectively, our results establish an atomiclevel description of the underlying mechanism regulating metal/oxide interfaces for the optimization of heterogeneous catalysis.

Electric double layer formation often governs the rate and selectivity of CO2 electrochemical reduction. Ionic correlations critically define double layer properties that are essential to electrocatalytic performance, including capacitance and localization of potential gradients. However, the influence of ionic correlations on CO2 electroreduction remains unexplored. Here, we use electrochemical conversion of CO2 to CO in ionic liquid-based electrolytes to investigate how the emergence of ionic correlations with increasing ion concentration influences reaction rates and selectivity. Remarkably, we find substantial acceleration of potential-dependent CO2 reduction rates and enhancement of faradaic efficiency to CO at intermediate concentrations of 0.9 M ionic liquid in acetonitrile, a concentration regime that has not been studied previously. We find that onset potentials for CO2 reduction remain relatively unchanged at −2.01 V vs Ag/Ag+ from 0.025 M up to 1.1 M and increase to −2.04 V vs Ag/Ag+ in the limit of neat ionic liquids. Hence, the acceleration of CO2 reduction we observe originates from the amplification of potential-dependent driving forces, as opposed to changes in onset potential. Importantly, our findings are general across cocatalytic and noncatalytic ions. We propose that concentrations of maximum reactivity correspond to conditions where electric double layers exhibit the strongest screening, which would localize electric fields to stabilize polar intermediates. Our study demonstrates that tuning bulk electrostatic screening lengths via modulation of ionic clustering provides a general approach to accelerating both inner-sphere and outer-sphere electrochemical reactions.

Light-driven synthesis of plasmonic metal nanostructures has garnered broad scientific interests. Although it has been widely accepted that surface plasmon resonance (SPR)-generated energetic electrons play an essential role in this photochemical process, the exact function of plasmon-generated hot holes in regulating the morphology of nanostructures has not been fully explored. Herein, we discover that those hot holes work with surface adsorbates collectively to control the anisotropic growth of gold (Au) nanostructures. Specifically, it is found that hot holes stabilized by surface adsorbed iodide enable the site-selective oxidative etching of Au0, which leads to nonuniform growths along different lateral directions to form six-pointed Au nanostars. Our studies establish a molecular-level understanding of the mechanism behind the plasmon-driven synthesis of Au nanostars and illustrate the importance of cooperation between charge carriers and surface adsorbates in regulating the morphology evolution of plasmonic nanostructures.