Wavelength-Dependent Selective Acceleration of CO₂ Reduction and H₂ Evolution Using a Plasmonic Gold Nanorod Electrode

A plasmonic electrode shows localized surface plasmon resonance (LSPR) at an intended wavelength based on the design of its nanostructure, and LSPR excitation is known to accelerate electrochemical reactions. In this study, we synthesized two types of gold nanorod, with and without platinum modification, and prepared a composite electrode consisting of these nanorods. Upon LSPR excitation, the gold nanorods showed enhanced carbon dioxide (CO2) reduction, whereas the platinum-modified gold nanorods promoted hydrogen (H2) evolution. Because these activations were induced at different wavelengths owing to the different aspect ratios of the nanorods, the composite electrode showed a change in Faradaic efficiencies for CO2 reduction and H2 evolution depending on the irradiation wavelength at a constant potential. Thus, this type of photoelectrode would enable the wavelength-dependent production of selected compounds and the use of irradiation wavelength as a parameter of photoelectrochemical reactions.