Bimetallic (100) Rh/Au electrodes for the oxygen reducton reacton (orr)

ESTEFANIA COLOMBO; ERICA SCHULTE; MAURICIO ARCE; PAOLA QUAINO

Santa Fe

Conferencia; VI San Luis Conference on surfaces, interfaces and catalysis; 2018

Studies of structure and reactiitt of htbrid Rh/Au surfaces were performed with the purpose of designing new electrode materials, specifcally cathode materials for cells fuels, with superior performance for the oxtgen reduction reaction (orr).Studies were focus on the Rh/Au intermetallic line, and we could demonstrate that in surfaces containing more than one metal there are interactons between them that modift the behavior of the intermetallic region, faioring the orr. This work is in line with other studies carried out bt our research group, in which other combinatons of metals haie beensuccessfully tested. Two possible pathways, associative and dissociative, were considered for the orr. In an acidic medium, the global reaction is: O 2 + 4H + + 4e - → 2H 2 O; but in addition to the complete reduction there is a competing process that should be avoided, in which hydrogen peroxide is produced. This research were carried out based on first principles calculations,within the framework of the density functional theory (DFT) to investigate the adsorption and/or the dissociation of the species participating in the reaction. The work is oriented to evaluate the bimetallic junction for the orr. Through theoretical evidences, it is possible to understand the energetic, geometric and electronic effects that govern the electrocatalytic activity of the bimetallic electrode materials.The effect of the bimetallic junction on the stability of the intermediates O 2 and OOH was evaluated by means of geometrical and energetic parameters; being the intermediates preferably adsorbed on Rh atoms, but presenting in some cases higher adsorption energies compared with bare metals. The kinetics of the O?O bond breaking in O 2 ∗ and OOH ∗adsorbed intermediates and the influence of the Rh/Au junction were studied bt means of the nudge elastic-band method, which analyzes the minimum energy paths for the following reaction steps:- Dissociative adsorption of the oxygen molecule - on 1Rh/2Au and 2Rh/1Au.- Dissociative adsorption of the superoxide species - on 1Rh/2Au and 2Rh/1Au.We observed variations in the behavior of the intermediaries due to the presence of the bimetallic junction, conforming that there is a synergetic effect in the intermetallic region, mainly caused by modifications induced in the electronic structure of each metal in contact. For some combinations, adsorption energies of these intermediates are greater (more negative values) than for bare Rh and Au metals, providing evidence of a synergetic behavior between these metals. Abarrierless process for the scission of O2∗ was found in Rh/Au for the higher Rh ratios. For Rh/Au with lower Rh ratios, the barriers were lower than for pure Au surfaces, suggesting a highly reactive surface towards the orr. The O?O scission of the OOH∗ was found to be a barrierless process in Rh/Au systems, implying that the reduction of O2 in these systems proceeds via the full reduction of O2 to H2O, avoiding H2O2 formaton. And fnally, the scission of H2O2 was resulted to be a barrierless process in Rh/Au , demonstrating that the hybrid junction reassembles the properties of pure Rh. To summarize, our resultsimply that Rh/Au, mixed in a proper ratio, can also be a great electrode material for orr, ia ea, Rh loading could be reduced without losing much cataltyc activity towards the orr if properly combined with gold.