Plasmon-Enhanced Asymmetry in the Charge Distribution Explains the Increased H2 Production Rate from Formic Acid with a PdTipped Au Nanorod

Plasmonic nanostructures offer a promising route to increase efficiency in photocatalysis. This study provides a microscopic explanation for the enhanced H2production rate from formic acid under plasmonic-resonance conditions of the photocatalytic reaction on a Pd-tipped Au nanorod (NR), observed experimentally. Using electron-dynamics multiscale simulations for a system composed of a classical Au NR and a DFT-described subsystem of Pd atoms and adsorbed reaction intermediates (bidentate HCOO* and H*) in the presence of a femtosecond pulse, we observe a net electron injection into HCOO*, which takes on the highest value in plasmon-resonance conditions. We find an asymmetry in the injection of electronic charge into the two oxygen atoms even in the absence of NR. The plasmonic field in resonant conditions significantly increases this asymmetry, thus representing the key to understanding the greater efficiency in H2generation, since the next reaction step is the formation of the monodentate HCOO*. Also, a greater spatial heterogeneity of the charge on the Pd surface has been found in the case of resonance with the NR plasmon, which can promote the advancement of the reactive process.