Hot hole direct photoelectrochemistry of Au NPs: Interband versus Intraband hot carriers

Optically-excited gold nanoparticles (Au NPs) generate plasmon oscillations that induce hot charge carriers by non-radiative decay. These hot charge carriers are to improve the energy conversion efficiency of photochemical and photoelectrochemical reactions. Depending on the mode of excitation (i.e., interband or intraband), the energy of the hot electrons and hot holes vary significantly. Although, both interband and intraband hot carriers were used separately for driving photoelectrochemical reactions, a comparison between these two types of hot carriers in directly driving electrochemical reactions, without the use of semiconductive layers, is still lacking. Herein, we compare the hot hole mediated photocurrent generation efficiencies of Au NPs deposited on screen printed carbon electrodes when excited at 405 nm and 532 nm wavelengths that correspond to interband and intraband excitation, respectively. Oxidation of ascorbic acid was used as a model reaction system due to its strong hole scavenging properties. Interband excitations showed higher anodic photocurrents than the photocurrent achieved from intraband excitation. The efficiency of photocurrent generation was found to be strongly dependent on the surface distribution of Au NPs. The optimized electrodes, obtained by varying the size and density of Au NPs on the electrode surface, were further used to evaluate methanol electro-oxidation with both interband and intraband excitations. An anodic peak current density of 56 µA/µg was achieved when interband carriers were excited, which is ∼30% higher than the current achieved with intraband excitation (43 µA/µg).