Morphology and Active-Site Engineering for Stable Round-Trip Efficiency Li-O 2 Batteries: A Search for the Most Active Catalytic Site in Co 3 O 4

Transcription

1 Supporting information: Morphology and Active-Site Engineering for Stable Round-Trip Efficiency Li-O 2 Batteries: A Search for the Most Active Catalytic Site in Co 3 O 4 Kyeongse Song, Eunbi Cho and Yong-Mook Kang *, Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul, , Korea. AUTHOR INFORMATION Corresponding Author * dake1234@dongguk.edu (Prof. Y.-M. Kang)

2 EXPERIMENTAL METHOD Chemicals and materials Cobalt(II) acetate tetrahydrate (98%), Cu(C 2 H 2 O 4 ) (97%), PVP (M W 55,000), Ethylene glycol ( 99%), and benzyl amine (99%) were purchased from Aldrich and used without further purification. Synthesis of {112} faceted Co 3 O 4 plate 0.5g of Co(CH 3 COO) 2 4H 2 O were dissolved in ethylene glycol (EG, 36 ml) by ultra-sonication. After the solution were changed into a transparent purple colour. Subsequently, the solution was heated at 200 ºC for 5 h under vigorous stirring. During the reaction, the solution color turned to mauve. The reaction mixture was cooled down to room temperature. The suspension was separated by centrifugation, washed with deionized water and ethanol mixture three times, and then dried in a vacuum at 60 ºC for 6 h. Finally, the dried powders were fired at 350 C for 2 h and cooled down naturally to room temperature. Synthesis of {001} faceted Co 3 O 4 cube NaOH (0.01 mol) and Co(NO 3 ) 2 (0.04 mol) were dissolved in D. I. water with vigorous stirring for 30 min. Then, the solution transferred to a Teflon-lined stainless-steel autoclave with a capacity of 100 ml, sealed and maintained at 180 ºC for 5h. After cooling to room temperature, the resulting suspensions were separated by centrifugation, washed with deionized water and ethanol each five times, and then dried in a vacuum at 60 ºC for 6 h.

3 Synthesis of {111} faceted Co 3 O 4 octahedron Lithium nitrate (6.89g) powder measured into round flask and heat at 400 ºC by using heating mantle with vigorous stirring. After the lithium nitrate fully transformed to pale liquid phase, the fine Co(NO 3 ) 2 (0.2 mmol) powder was added and maintained at 400 ºC for 30 min. After cooling to room temperature, the resulting product was washed with deionized water and ethanol each five times, to remove lithium nitrate and impurity salts and then dried in a vacuum at 60 ºC for 6 h. Characterization of Co 3 O 4 crystals Co 3 O 4 crystals were characterized by an XRD (Bruker/New D8 Advance) diffractometer using graphite-mono-chromatized Cu Kα radiation at 40 kv and 40 ma, and a field emission scanning electron microscope (FE-SEM; JEOL JSM-6700F, operated at 10 and 30 kv). Bright-field TEM imaging and fast fourier transform diffraction pattern were conducted using a Tecnai G2 F30 operated at 300 kv accelerating voltage. Chemical compositions were analyzed using X-ray photoelectron spectroscopy (XPS; Thermo Fisher Scientific Co. theta probe base system). All binding energies were referenced to the C 1s peak (285 ev).

4 Figure S1 (a) SEM image of Co 3 O 4 cube. (b) SEM image of Co(OH) 2 plate. (c) SEM image of Co 3 O 4 plate. (d) SEM image of Co 3 O 4 cube. (e) SEM image of Co 3 O 4 plate.

5 Figure S2 The XRD patterns of Co 3 O 4 cube and Co 3 O 4 plate.

6 Figure S3 (a) Schematic diagram for discharge reaction of {111} faceted Co 3 O 4 octahedron. (b) SEM image of {111} faceted Co 3 O 4 octahedron, after discharge (c) and charge (d). (e) Electrochemical performance comparing as synthesized samples prepared in the ratio 40: 45: 15, catalyst, ketjen black, binder respectively. (f) Table for BET surface area and total pore volume. (g) Relationship between catalytic performance, BET surface area, Co 3+ concentration and Li 2 O 2 nucleation site.

7 Figure S4 The galvanostatic discharge/charge profiles of (a) the {112} faceted Co 3 O 4 plate and (b) the {001} faceted Co 3 O 4 cube of the 1 st, 5th, 10 th, 15 th, 20 th, 25 th and 30 th cycle. The discharge/charge voltage profiles during the initial ten cycles for (c) {112} faceted Co 3 O 4 plate, and (d) {001} faceted Co 3 O 4 cube.

8 Figure S5 Characterization (SEM) of discharged cathode in limited capacity condition (500 mah/g) including {001} faceted Co 3 O 4 cube and {112} faceted Co 3 O 4 plate as the cathode catalyst, respectively.