Size-selective electrocatalytic activity of (Pt)(n)/MoS2 for oxygen reduction reaction

Abstract

In the present work, we have investigated the electrocatalytic activity of the oxygen reduction reaction (ORR), O-2 + 4H(+) + 4e(-) -> 2H(2)O, for (Pt)(n) clusters (n = 1, 2, 3, 5, 7, 10 and 12) adsorbed on semiconducting (2H) and metallic (1T) MoS2 monolayers using first principles density functional theory. We have considered four elementary reactions involved in ORR within a unified electrochemical thermodynamic framework and the corresponding Gibbs adsorption free energies of the key intermediates (*OOH, *O, *OH) associated with each step have been calculated. The results indicate that the reduction of adsorbed hydroxyl (*OH) to water (*OH + H+ + e(-) -> H2O) is the bottleneck step in the ORR process. The adsorption free energy of *OH (Delta G(*OH)) is found to be the thermodynamic descriptor for the present systems. Eventually, the ORR activity has been described as a function of Delta G(*OH) and a volcano plot predicting (Pt)(7)/2H- MoS2 as the best ORR catalyst amongst the (Pt)(n)/MoS2 heterosystems with an overpotential value of 0.33 V has been established. Our finding proposes a new promising electrocatalyst towards better activity for ORR with very small amount of Pt loading.