Rational design of metal catalysts for fuel cell electrodes has eluded researchers due to the limited understanding of the mechanisms of the surface reactions. This limitation is largely due to the inaccessibility of electrode | electrolyte interface to surface probes. This interface is known as the electric double layer (EDL) due to the charge accumulated on the metal surface due to adsorption and counter charge in the solution at the interface. While several factors influence the molecular level picture of the EDL, the interface always consists of large electric fields and solvating water molecules. Any attempt to understand the mechanisms of electrochemical reactions must consider how those factors affect the surface chemistry. Understanding how the EDL influences surface energetics is critical to the study of electrocatalysis.

We have developed an EDL model using DFT to study the oxygen reduction reaction on Pt(111). In this model, the solution consists of a weakly adsorbed protonated water cluster, while the charge gradient is modeled using homogeneous electric fields. Our model suggests an initial electron transfer step with simultaneous proton transfer, as opposed to the initial dissociation of O2 that occurs in non-electrochemical oxygen reduction. We present these results and discuss how both components of the EDL influence the reaction pathway and energetics.