www.advenergymat.de FULL PAPER 1700391 (1 of 10) © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Hierarchical Porous Carbonized Co 3 O 4 Inverse Opals via Combined Block Copolymer and Colloid Templating as Bifunctional Electrocatalysts in Li–O 2 Battery Seol A. Cho, Yu Jin Jang, Hee-Dae Lim, Ji-Eun Lee, Yoon Hee Jang, Trang-Thi Hong Nguyen, Filipe Marques Mota, David P. Fenning, Kisuk Kang,* Yang Shao-Horn,* and Dong Ha Kim* DOI: 10.1002/aenm.201700391 hybrid electrical vehicles. [1–8] In metal–air batteries, a metal anode such as Li or Zn is coupled with an air breathing cathode that utilizes high purity oxygen as the reactant in electrochemical reactions. Among the emerging metal–air batteries, rechargeable lithium–air batteries (also called Li–O 2 batteries) are considered one of the most attractive high energy storage and conversion electrical energy devices due to their extremely high theoretical energy density. [9–12] Up to date, however, the successful commercialization of rechargeable Li–O 2 batteries still rely on an improvement of poor safety characteristics as the forma- tion of lithium dendrite, round-trip effi- ciency, and cycle life. [13–15] Several contri- butions of prime importance have been reported to enhance the battery perfor- mance by improving critical constituents including the Li anode, [16–18] operating atmosphere, [19,20] binders, [21] solvents, [22] and lithium salts. [23,24] Albeit the extension of the above-mentioned exploratory works, the choice of the air cathode has been often underlined as the dominating issue in the performance of Li–air batteries. Accordingly the bifunctional activity of the cathode in Li–O 2 battery, i.e., oxygen reduction reaction (ORR) and oxygen evo- lution reaction (OER) is the key factor of battery performance. Hierarchically organized porous carbonized-Co 3 O 4 inverse opal nanostruc- tures (C-Co 3 O 4 IO) are synthesized via complementary colloid and block copolymer self-assembly, where the triblock copolymer Pluronic P123 acts as the template and the carbon source. These highly ordered porous inverse opal nanostructures with high surface area display synergistic properties of high energy density and promising bifunctional electrocatalytic activity toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). It is found that the as-made C-Co 3 O 4 IO/Ketjen Black (KB) composite exhibits remarkably enhanced electrochemical performance, such as increased specific capacity (increase from 3591 to 6959 mA h g -1 ), lower charge overpotential (by 284.4 mV), lower discharge overpotential (by 19.0 mV), and enhanced cycla- bility (about nine times higher than KB in charge cyclability) in Li–O 2 battery. An overall agreement is found with both C-Co 3 O 4 IO/KB and Co 3 O 4 IO/KB in ORR and OER half-cell tests using a rotating disk electrode. This enhanced catalytic performance is attributed to the porous structure with highly dis- persed carbon moiety intact with the host Co 3 O 4 catalyst. S. A. Cho, Dr. Y. J. Jang, J.-E. Lee, Dr. Y. H. Jang, Dr. T.-T. H. Nguyen, Dr. F. M. Mota, Prof. D. H. Kim Department of Chemistry and Nano Science Ewha Womans University 52, Ewhayeodae-gil, Seodaemun-gu, Seoul 03760, Republic of Korea E-mail: dhkim@ewha.ac.kr Dr. H.-D. Lim, Prof. K. S. Kang Department of Materials Science and Engineering Seoul National University 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea E-mail: matlgen1@snu.ac.kr Dr. Y. H. Jang Photo-Electronic Hybrids Research Center Korea Institute of Science and Technology (KIST) 5 Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea Prof. D. P. Fenning Department of Nanoengineering University of California San Diego 9500 Gilman Dr., La Jolla, CA 92093, USA Prof. Y. Shao-Horn Department of Materials Science and Engineering Massachusetts Institute of Technology 77 Massachusetts Ave, Cambridge, MA 02139, USA E-mail: shao-horn@mit.edu The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.201700391. Lithium-Oxygen Batteries 1. Introduction The fast depletion of fossil fuels and extended environmental concerns have inspired active research on the utilization and storage of clean and sustainable energy. Among various energy storage technologies, rechargeable metal–air batteries have the highest potential for next generation electrical vehicles and Adv. Energy Mater. 2017, 1700391