Electrochemically-Assisted Site-Selective Redox Reactions through Plasmonic Hole/Electron Ejection
Authors: Nishi Hiroyasu , Tatsuma Tetsu 
Published: December 2020

Anisotropic growth and modification of plasmonic nanoparticles have been of significant interest because their optical properties are depending strongly on anisotropy of the particle shape and environment.1,2 Some researchers previously reported anisotropic reduction reactions including Ag and Au nanoparticle growth3,4 and Pt deposition onto Au nanoparticles5 under excitation of localized surface plasmon resonance (LSPR). Recently, our group demonstrated “site-selective” oxidative dissolution of Ag nanoparticles6-8 and deposition of PbO2 onto Au nanoparticles9 on the basis of plasmonic hot hole ejection10 assisted by a semiconductor such as TiO2. Irradiation of light with different wavelengths resulted in oxidation reactions at different sites corresponding to excited LSPR modes. However, only oxidation reactions are possible for nanoparticles on n-type semiconductors (electron transport layers). In this study, we found that both oxidation and reduction reactions, including oxidative PbO2 deposition, coordinative dissolution of Au in the presence of Cl-, and reductive deposition of Pt, take place site-selectively on Au nanoparticles through electrochemically-assisted plasmonic hole/electron ejection without using a semiconductor.
A Au nanocube-depoisted indium tin oxide (ITO) electrode was immersed in an electrolyte solution containing Pb(NO3)2, KCl, or H2[PtCl6] and potential of +0.95, +0.85, or +0.55 V vs. Ag|AgCl (sat. KCl) was applied to the electrode in a three-electrode system, respectively. Distal or proximal mode2 was excited by visible light after the current became almost constant in the dark. The figure shows SEM images of the electrode surface after light irradiation. Oxidative PbO2 deposition, Au dissolution, and reductive Pt deposition are observed preferentially at the top face of the nanocubes after distal mode excitation (panels a, b, and c, respectively) while the reactions proceeded at the interfacial region between the nanocube and ITO in the case of proximal mode (panels d, e, and f, respectively).11 Similar site-selective reactions were also observed on Au nanorods under excitation of transverse and longitudinal modes.11 These nanofabrication techniques are potentially applicable not only to control of LSPR properties but also to fabrication of high-performance plasmonic photocatalysts and chiral plasmonic materials.

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Figure 1