Unraveling the Molecular Mechanism of H₂O₂ Production on Au-Pd Nanoalloy Surfaces

Oxygen reduction reaction (ORR) can proceed along two distinct pathways: the 4-electron pathway and the 2-electron pathway. The 4-electron pathway holds significant value in fuel cell technology, whereas the 2-electron pathway plays a crucial role in the industrial production of H₂O₂. Accurate prediction of the catalytic selectivity in the ORR stands as a pivotal factor in designing effective catalyst materials. It has been experimentally demonstrated that Au-Pd nanoalloy exhibit a high selectivity toward electrocatalytic H₂O₂ production. However, based on the widely employed computational hydrogen electrode method, the production of H₂O on the surface of Au-Pd nanoalloy is more thermodynamically favorable, which shows a discrepancy with experimental results. In this work, we systematically investigate the influence of aqueous environment as well as electrode potential toward the ORR employing state-of-the-art ab initio molecular dynamics and metadynamics simulations. Our work reveals that the water molecules above the Au-Pd nanoalloy surface can alter the adsorption behavior of O₂ and weaken the interaction between metal atom in the catalyst and oxygen atom in O₂, therefore contributing to a high selectivity of Au-Pd nanoalloy toward H₂O₂ production. With a more negative electrode potential, the stability of H₂O₂ will decrease, and the corresponding selectivity will be lowered. These discoveries provide a dynamic perspective elucidating efficient H₂O₂ production on Au-Pd nanoalloy surfaces. Furthermore, they underscore the paramount significance of both the aqueous environment and electrode potential in shaping the ORR process.