Some of the biggest challenges to the commercialization of the polymer electrolyte membrane (PEM) fuel cells include the cost, performance, and durability of its components. For example, state-of-the-art Pt-based cathode electrocatalysts are expensive, have limited activity, and are unstable under the harsh operating environment of the fuel cell. Hence there is a need to develop alternative catalysts that are inexpensive, highly active, and stable. For designing these catalysts, an atomic level understanding of the influence of factors like surface hydration, oxidation, segregation, and composition, on surface reactivity can be critical. However, in most cases, it is extremely difficult to obtain such information from experimental measurements alone.

We have used density functional theory (DFT) calculations with plane wave basis VASP code to gain some insights into the oxygen reduction reaction (ORR) occurring on the cathode of the PEM fuel cell. For this, the most stable (111) surfaces of widely used Pt-based catalysts (like Pt, Pt₃Co) are modeled. The adsorption of H₂O to form a monolayer is found to be favorable on these surfaces, and Pt skin formation is predicted to be stable on Pt-transition metal alloys in the presence of water. The adsorption of various ORR intermediates on these surfaces is probed and the possible reaction pathways are identified. Results indicate that molecular oxygen dissociation is facile on most of these hydrated surfaces and the addition of first proton to form hydroxyl could be the rate limiting step. The first principles predictions are further correlated with the experimental electrochemical activity results of these Pt-based catalysts and a good fit is obtained. This approach can then be used to guide the development of new alloy combinations and compositions with improved ORR activity.