Single Crystalline Co 3 O 4 Nanocrystals Exposed with Different Crystal Planes for Li-O 2 Batteries

Transcription

1 Supplementary Information Single Crystalline Co 3 O 4 Nanocrystals Exposed with Different Crystal Planes for Li-O 2 Batteries Dawei Su, 1,2* Shixue Dou, 1* and Guoxiu Wang 2* 1 Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia 2 Centre for Clean Energy Technology, School of Chemistry and Forensic Science, University of Technology Sydney, Broadway, Sydney, NSW 2007, Australia Corresponding authors: Dawei Su: Dawei@uow.edu.au Tel: Fax: Shixue Dou: shi@uow.edu.au Tel: Fax: Guoxiu Wang: Guoxiu.Wang@uts.edu.au Tel: Fax:

2 Table S1. Coordinatively unsaturated Co 2+ and Co 3+ Crystal planes Unsaturated Co 2+ * Unsaturated Co 3+ Twofold Threefold Threefold Fourfold Co 2+ Co 2+ Co 3+ Co 3+ {100} {110} {111} {112} *4 ¼ corner occupied ions equal one ion 2 ½ surface occupied ions equal one ion Fivefold Co 3+ 2

3 Scheme S1. Schematic to introduce the mechanism through which the hexagonal Co(OH) 2 nanoplatelets is converted into Co 3 O 4 nanoplatelets, maintaining the single crystal feature. The crystal mismatch between Co(OH) 2 and Co 3 O 4 is below 2 % from the calculation based on the crystal planes of (1 0), (100), and (010) in Co(OH) 2 and (0 2), (2 0), and (20 ) in Co 3 O 4, and the interfacial angles between each other of these crystal planes of these two crystals are the same (60 ). 3

4 Scheme S2. Schematics to introduce the mechanism through which the (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar is converted into Co 3 O 4 nanolaminar, maintaining the single crystal feature. The crystal mismatch between (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O and Co 3 O 4 is below 2% from the calculation based on the crystal planes of (200), (012), and (212) in (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O and (2 0), ( 11), (11 ) in Co 3 O 4, and the interfacial angles between each other of these crystal planes of these two crystals are the same. 4

5 Figure S1. FESEM images of Co 3 O 4 nanocubes with different magnifications. The uniform cubic particle shape and homogeneous particle size distribution (less than 40 nm) can be seen. 5

6 Figure S2. a-c FESEM images of pseudo octahedral Co 3 O 4 nanocrystals with different magnifications. a is the low magnification image, from which the uniform particle size distribution (less than 50 nm) can be seen. Few particles with pseudo octahedral shape can be seen in b and c, which are the high magnification FESEM images. As illustrated by the geometrical models (d), the particle shape can be seen as the octahedron with a large truncation on the two top points and slight truncation on the four edges. d presents the particles shape in c using the geometrical model from different projected direction. 6

7 Figure S3. FESEM images of Co 3 O 4 nanosheets with different magnifications. The uniform faceted shape and homogeneous particle size (less than 40 nm) distribution can be seen according to the different magnification images. 7

8 (002) (003) (111) (200) (013) (021) (202) (004) Intensity (A.U.) (100) (110) (012) (001) (101) a Co(OH) 2 JCPDS Card No (degrees) Figure S4. a. X-ray diffraction pattern of the Co(OH) 2 nanocrystals, all the diffraction peaks match well with the crystal structure of the hexagonal Co(OH) 2 phase (space group of P-3M1 (163)), exhibiting a well-crystalline phase (JCPDS Card No , a = b = nm, c = nm, γ = 120 ) without any impurity phase. b. SEM image of the hexagonal Co(OH) 2 nanoplatelate. 8

9 Figure S5. High magnification FESEM image of hexagonal Co 3 O 4 nanoplatelets converting from the {001} facets exposed hexagonal Co(OH) 2 nanoplatelets, showing that the thickness of each nanoplatelet is around 20 nm. 9

10 (330) (124) (432) Intensity (A.U.) (200) (102) (300) (220) (130) (202) (221) (502) (311) (122) (101) (302) (201) a (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6.4H 2 O JCPDS Card No (degrees) Figure S6. A. X-ray diffraction pattern of the (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanocrystals, all the diffraction peaks match well with the crystal structure of the hexagonal (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O phase (space group of P63 (173)), exhibiting a well-crystalline phase (JCPDS Card No , a = b = nm, c = nm, γ = 120 ) without any impurity phase. B. SEM image of (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminars. 10

11 Figure S7. FESEM images of Co 3 O 4 nanolaminar converting from the (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar. a and b are low magnification SEM images, in which the uniform paper-liked Co 3 O 4 nanolaminars fold together inheriting from the precursor can be seen. c and d are the high magnification SEM images showing the thickness of each monolayer Co 3 O 4 nanolaminar is around 10 nm. Meanwhile, the tiny pores regularly arranging in the Co 3 O 4 nanolaminar can be observed. 11

12 Figure S8. a. Low magnification TEM image of the Co 3 O 4 nanocubes, in which it can be seen the homogeneous particle size distribution. b. High magnification TEM image of few Co 3 O 4 nanocubes, in which it can be seen each of them has the perfect sharp edges and corners and well-defined faces. c. A single free standing Co 3 O 4 nanocube, the same as Figure 3 a1, but with a higher magnification, in which it can be seen regular lattice arrangement on this whole projected surface. d is lattice resolution HRTEM image recording from the dotted rectangular area of c. Inset of d is the corresponding FFT image with indexed crystal planes, in which more lattice information can be collected to confirm the {100} facets dominate the Co 3 O 4 nanocube. 12

13 Figure S9. a. Low magnification TEM image of the pseudo octahedral Co 3 O 4 nanocrystals, in which the homogeneous particle size distribution can be seen. b. High magnification TEM image. It shows two free standing pseudo octahedral Co 3 O 4 nanocrystals, which have rhombic out frame with truncation on the four corners because of the special projection direction, and the crystal plane lattice can be seen clearly confirming their well single crystalline feature. c is lattice resolution HRTEM image recorded from the dotted rectangular area 1 of b. d is indexed FFT pattern images taken from rectangular area 2 of b. 13

14 Figure S10. a. Low magnification TEM image of the {110} facets exposed Co 3 O 4 nanosheets, in which the homogeneous particle size distribution (less than 40 nm) can be seen. b. High magnification TEM image of the few Co 3 O 4 nanosheets. It can be seen each of them has the perfect sharp edges and corners and well-defined faces. c. High magnification TEM image of a single free standing Co 3 O 4 nanosheet, in which the (0 2) crystal plane can be seen, proving its well single crystalline feature. d is the FFT pattern image taken from the whole single nanosheet of c. The spots can be indexed along the [110] zone axis of spinal Co 3 O 4 which indicates that its surface is exposed with {110} facets. 14

15 Figure S11. Low magnification TEM image of the hexagonal Co(OH) 2 nanoplatelets, in which the homogeneous particle size distribution and hexagonal shape of particle can be seen.. 15

16 Figure S12. a. Low magnification TEM image of the (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar, in which the homogeneous thickness distribution can be seen. b. High magnification TEM image of few pieces paper-liked (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar, in which we can see that each of them has the perfect smooth surface. c. The SAED pattern taken from a monolayer (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar as marked by the doted rectangle area in b shows perfect rectangle diffraction spots array, indicating the single crystalline feature of as-prepared (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar. The spot patterns can be indexed as (200), (212), and (012) along the [02 ] zone axis, indicating asprepared (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminars are exposed with {02 } facets. d. High magnification of one piece of paper-liked (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar. e is lattice resolution HRTEM image recording from the dotted rectangular area of d, in which the (212), (012), and (200) crystal planes with 0.45, 0.23, and 0.29 nm d-spacings, respectively, can be observed. Together with its corresponding indexed FFT pattern image (f), it can be confirmed that the as-prepared (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar single crystal has the dominantly exposed with crystal planes of {02 }. 16

17 Figure S13. a. Low magnification TEM image of the Co 3 O 4 nanolaminar, in which monolayer Co 3 O 4 nanolaminar with the mesoprous structure and homogeneous thickness can be seen. b. TEM image taken from a corner of monolayer Co 3 O 4 nanolaminar, in which the mesoporous architecture can be seen. Although with this mesoporous architecture, the asprepared Co 3 O 4 nanolaminar still maintain single crystalline feature. It can be proved by the SAED patterns taken from the free standing monolayer Co 3 O 4 nanolaminar as shown in c, in which the (11 ), ( 11), and (2 0) crystal planes along the [112] zone axis can be indexed. The dot SAED patterns imply the single crystalline nature of the mesoporous Co 3 O 4 nanolaminar. d is a high magnification TEM image showing detail of inner nanosize pores which form an integrated porous architecture. The average pore size was determined to be about 3 nm. e shows a lattice resolved HRTEM image, and f is its corresponding indexed FFT pattern image, in which the lattice can be determined to be the (11 ), (2 0), and ( 11) crystal planes with 0.46, 0.28, and 0.24 nm d-spacings respectively. It can be confirmed that the Co 3 O 4 nanolaminar converting from the facets exposed (NH 4 ) 2 Co 8 (CO 3 ) 6 (OH) 6 4H 2 O nanolaminar has the single crystal character and dominantly exposed with crystal planes of {112}. 17

18 BJH Adsorption da/dw Pore Area/m²/g nm BJH Adsorption da/dw Pore Area/m²/g nm 5 4 a 3 2 Pore area m 2 /g Pore width/nm b 80 Pore area m 2 /g Pore Width/nm Figure S14. The adsorption pore area distribution versus the pore size of {111} facets exposed Co 3 O 4 nanoplatelets, a, {112} facets exposed Co 3 O 4 nanolaminars, b. The integrated BJH adsorption pore areas of them are and m 2 g -1 respectively, which were subtracted from the surface areas of them for the comparison. 18

19 Capacity (ma h g -1 ) 6000 Charge Discharge Cycle number Figure S15. Cycling performance of Co 3 O 4 nanoplatelets loaded CNT electrode at current density of 200 ma g -1 19