Bifunctional MnO2-Coated Co3O4 Hetero-structured Catalysts for Reversible Li-O2 Batteries

Abstract

The structural design and synthesis of effective cathode catalysts are important concerns for achieving rechargeable Li-O2 batteries. In this study, hexagonal Co3O4 nanoplatelets coated with MnO2 were synthesized as bifunctional catalysts for Li-O2 batteries. The oxygen reduction reaction catalyst (MnO2) was closely integrated on the surface of the oxygen evolution reaction catalyst (hexagonal Co3O4) so that this hetero-structured catalyst (HSC) hybrid would show bifunctional catalytic activity in Li-O2 batteries. A facile synthesis route was developed to form a unique HSC structure, with {111} facet-exposed Co3O4 decorated with perpendicularly arranged MnO2 flakes. The catalytic activity of the HSCs was controlled by tuning the ratio of Co to Mn (the ratio of OER to ORR catalysts) in the hybrids. With the optimized Co3O4-to-MnO2 ratio of 5:3, a Li-O2 cell containing the HSC showed remarkably enhanced electrochemical performance, including discharge capacity, energy efficiency, and especially cycle performance, compared to cells with a monofunctional catalyst and a powder mixture of Co3O4 and MnO2. The results demonstrate the feasibility of reversible Li-O2 batteries with bifunctional catalyst hybrids.