Electrocatalytic Study of the Oxygen Reduction Reaction at Gold Nanoparticles in the Absence and Presence of Interactions with SnO x Supports.

Abstract

Here we report that density functional theory (DFT) can be used to accurately predict how Au nanoparticle (NP) catalysts cooperate with SnO x ( x = 1.9 or 2.0) supports to carry out the oxygen reduction reaction (ORR). Specifically, dendrimers were used to encapsulate AuNPs and prevent their interactions with the underlying SnO x supports. After removal of the dendrimers, however, the AuNPs are brought into direct contact with the support and hence feel its effect. The results show that both SnO1.9 and SnO2.0 supports strongly enhance the electrocatalytic properties of AuNPs for the ORR. In the case of AuNP interaction with a SnO1.9 support, the number of electrons involved in the ORR ( neff) increases from 2.1 ± 0.2 to 2.9 ± 0.1 following removal of the dendrimers, indicating an increased preference for the desired four-electron product (water), while the overpotential decreases by 0.32 V. Similarly, direct interactions between AuNPs and a SnO2.0 support result in an increase in neff from 2.2 ± 0.1 to 3.1 ± 0.1 and a reduction of the overpotential by 0.28 V. These experimental results are in excellent agreement with the theoretically predicted onset potential shift of 0.30 V. According to the DFT calculations, the observed activity enhancements are attributed to the existence of anionic Au resulting from electron transfer from surface oxygen vacancies within the SnO x supports to the AuNPs. This theoretical finding was confirmed experimentally using X-ray photoelectron spectroscopy. Importantly, the calculations reported here were performed prior to the experiments. In other words, this study represents an unusual case of theory accurately predicting the electrocatalytic manifestation of strong metal support interactions.