Oxygen Evolution Reaction on the Fe3O4(001) Surface: Theoretical Insights into the Role of Terminal and Bridging Oxygen Atoms

Abstract

Model catalysts, where the structure of single-crystal materials with well-defined surface terminations can be determined at the atomic level, are useful systems to perform fundamental studies on electrocatalysis. The magnetite Fe3O4(001) surface, in particular, has been the focus of several studies aimed at characterizing its structure in vacuum in the presence of a water layer and interfaced with liquid water-based electrolytes. Recently, this system has also been investigated as a catalyst for the oxygen evolution reaction (OER), with the goal of correlating structural properties of the interface with catalytic performance and mechanism. In this work, we use first-principles simulations based on density functional theory to establish the structural, thermodynamic, and electronic properties of the Fe3O4(001) surface in contact with water. We compute the phase diagram of the magnetite/water system and address some open issues on the structural transitions observed experimentally among different surface terminations. We then address the stability in electrochemical environments, and we investigate the OER mechanism, considering reaction paths involving both terminal and bridging oxygen atoms. We find that different surface reconstructions can promote OER via different reaction sites and potential-determining steps, albeit with a similar energy cost. In particular, the bulk-truncated termination promotes OER via terminal oxygen atoms, and the potential-determining step is the dehydrogenation of the *OH group. On the (2×2)R45° reconstruction, on the other hand, OER proceeds via the bridging oxygen atoms, and the potential-determining step is the formation of the hydroperoxo.