Elucidating Challenges of Reactions with Correlated Reactant and Product Binding Energies on an Example of Oxygen Reduction Reaction

Using density functional theory (DFT), Pt-based sandwich catalysts have been studied to identify a strategy for improving the energetically unfavorable O hydration catalytic reaction (O + H_2O → 2OH) in fuel cells. The challenge for this type of reaction is that the reactant, O, and product, OH, have correlated binding energies, making the improvement of the overall energetics of the reaction problematic. We screened 28 different transition metals as the Pt-M-Pt sandwich middle layer and developed a new index that specifically describes the difficulty of the reaction which involves adsorbed atomic O as the reactant and adsorbed OH as the product. This index is found to predict well the barrier of the O hydration. In order to understand how the index can be optimized, we further studied the electronic density of states (DOS) to elucidate the DOS changes for the different Pt-M-Pt sandwiches. This gives insight on strategies that might be applied to improve the catalytic reactions where the reactant and product have correlated binding energies, which is in fact a common challenge in heterogeneous catalysis.