Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

Abstract

Cathode catalysts are the key factor in improving the electrochemical performance of lithium–oxygen (Li–O2) batteries via their promotion of the oxygen reduction and oxygen evolution reactions (ORR and OER). Generally, the catalytic performance of nanocrystals (NCs) toward ORR and OER depends on both composition and shape. Herein, we report the synthesis of polyhedral Au NCs enclosed by a variety of index facets: cubic gold (Au) NCs enclosed by {100} facets; truncated octahedral Au NCs enclosed by {100} and {110} facets; and trisoctahedral (TOH) Au NCs enclosed by 24 high-index {441} facets, as effective cathode catalysts for Li–O2 batteries. All Au NCs can significantly reduce the charge potential and have high reversible capacities. In particular, TOH Au NC catalysts demonstrated the lowest charge-discharge overpotential and the highest capacity of ~20 298 mA h g−1. The correlation between the different Au NC crystal planes and their electrochemical catalytic performances was revealed: high-index facets exhibit much higher catalytic activity than the low-index planes, as the high-index planes have a high surface energy because of their large density of atomic steps, ledges and kinks, which can provide a high density of reactive sites for catalytic reactions. Gold nanocrystals with high-index facets improve the electrochemical performance of lithium–oxygen batteries, find scientists in Australia. The high energy densities of lithium–oxygen batteries make them attractive for powering electric vehicles. The researchers investigated three differently shaped gold nanocrystals — cubic, truncated octahedral and trisoctahedral nanocrystals — for their effectiveness as cathode catalysts for lithium–oxygen batteries. They found that all three nanocrystals significantly reduced the charge potential while possessing high reversible capacities. Furthermore, the trisoctahedral nanocrystals, which have the highest index facets among three nanocrystals, exhibited the lowest charge–discharge overpotential and highest capacity. The researchers attribute the improved catalytic performance of crystals with high-index facets to higher index planes having greater surface energies resulting from the large density of atomic steps, ledges and kinks, which act as reactive sites for catalytic reactions. Polyhedral Au nanocrystals enclosed by a variety of index facets are prepared: cubic Au NCs enclosed by {100} facets; truncated octahedral Au NCs enclosed by {100} and {110} facets; and trisoctahedral Au NCs enclosed by 24 high-index {441} facets. It is found that high index facets exhibit much higher catalytic activity toward oxygen reduction and oxygen evolution reactions in Li–O2 batteries.