CONICET | Buscador de Institutos y Recursos Humanos

One of the biggest challenges of mankind nowadays, is to cope the energetic demand with energy sources that are both cheap and clean. Very promising solutions to this problem are the metal-based catalyst for hydrogen evolution and oxidation reactions (HER and HOR, respectively). The HER/HOR processes involve three elementary reactions: H+ + e- ↔ Had Volmer [1] Had + H+ + e- ↔ H2 ) Heyrovsky [2] 2Had ↔ H2 Tafel [3] In order to design the ultimate catalyst, it is fundamental to understand the mechanism of such reactions at the atomic level. This is, however, a very difficult task that requires combined efforts from the experimental and the theoretical fields. Theory can help us understanding phenomena beyond the experimental scope. As an example: By electrochemical techniques, it is possible to estimate the total coverage of hydrogen on metal surfaces, which is of great importance. However, there is to date no experimental technique that distinguishes the occupation of hydrogen adsorption sites. It is also unclear which reaction is the rate-determining step. Fortunately, theory can shed some light on these riddles. In this work, we present a model based on Kinetic Monte Carlo (KMC) that considers hydrogen adsorption, desorption, and diffusion on 111 and 100 facets. The activation energies for diffusion on clean surfaces were calculated by Density Functional Theory (DFT). The interaction between hydrogen neighbors can radically change the features of HER/HOR and therefore they cannot be neglected. In this model, the repulsion energy of hydrogen neighbors was taken as a combination of repulsion between isolated hydrogen pairs. The model allows us to compare HER/HOR features among several mechanisms, such as Vomer-Heyrovsky and Volmer-Tafel. This is a useful tool to explore how the HER/HOR behavior affects the configuration of hydrogen at the metal surface.