Mechanistic Insights into the H₂ Dissociation on Plasmonic Au Nanoparticles: Effect of Nanoparticle Structure and Pulse Properties on Charge-Driven Energy Transfer and Dissociation Efficiency

Induced hot electron transfer involving plasmonic nanoparticles leading to a chemical reaction is an intriguing alternative method to conventional catalytic processes. While plasmon-driven photodissociation is now well-known, a detailed mechanism is still lacking. In this study, using real-time time-dependent density functional tight binding (RT-TD-DFTB) theory with Ehrenfest dynamics, we have studied the mechanism for the dissociation of molecular hydrogen (H2) on Au nanoparticles with a range of sizes (up to 84 atoms) and shapes. Our results show that charge transfer is the primary process driving dissociation, with the threshold for dissociation being associated with a characteristic amount of charge transfer that leads to energy in the H2 bond above the dissociation energy. We have explored the influence of nanoparticle shape by considering two different kinds of nanostructures: nanorod and tetrahedral. We find that nanorod-shaped particles show lower pulse intensities at the dissociation threshold than tetrahedral ones, even though the plasmon energies are lower for the rod. The effect of pulse duration has been studied, and we see that a pulse time of less than 80 fs is more favorable for hydrogen dissociation due to competing effects from H2 desorption for longer pulses. In addition, we find two approaches for improving the dissociation efficiency: decreasing the size of the particle and increasing the number of H2 molecules on the particle.