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

The structural design and synthesis of effective cathode catalysts are important concerns for achieving rechargeable Li-O 2 batteries. In this study, hexagonal Co 3 O 4 nanoplatelets coated with MnO 2 were synthesized as bifunctional catalysts for Li-O 2 batteries. The oxygen reduction reaction catalyst (MnO 2 ) was closely integrated on the surface of the oxygen evolution reaction catalyst (hexagonal Co 3 O 4 ) so that this hetero-structured catalyst (HSC) hybrid would show bifunctional catalytic activity in Li-O 2 batteries. A facile synthesis route was developed to form a unique HSC structure, with {111} facet-exposed Co 3 O 4 decorated with perpendicularly arranged MnO 2 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 Co 3 O 4 -to-MnO 2 ratio of 5:3, a Li-O 2 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 Co 3 O 4 and MnO 2 . The results demonstrate the feasibility of reversible Li-O 2 batteries with bifunctional catalyst hybrids.