Supporting Information for

Transcription

1 Supporting Information for Ultrathin CoFe-Borate Layer Coated CoFe-LDH Nanosheets Array: A Non-Noble-Metal 3D Catalyst Electrode for Efficient and Durable Water Oxidation in Potassium Borate Chao You, 1,2 Yuyao Ji, 1,2 Zhiang Liu, 3 Xiaoli Xiong, 1,* and Xuping Sun 2,* 1 College of Chemistry and Materials Science, Sichuan Normal University, Chengdu , Sichuan, China 2 College of Chemistry, Sichuan University, Chengdu , China 3 College of Chemistry and Chemical Engineering, Qufu Normal University, Qufu , China * xiongxiaoli2000@163.com (X.X.); sunxp_scu@hotmail.com (X. S.) S1

2 Content Experimental Section Cross section SEM image....figure S1 HRTEM images after the water oxidation tests...figure S2 EDX spectrum.figure S3 Selected area electron diffraction patterns... Figure S4 SEM images after stability test......figure S5 XPS survey spectrum.....figure S6 Plot of LSV... Figure S7 Plot of CVs...Figure S8 Plot of TOF...Figure S9 Comparison of OER performance... Table S1 S2

3 Experimental Section Materials: Ti mesh (TM) was provided by Hangxu filters flag store, Hengshui, Hebei. Co(NO 3 ) 2 6H 2 O, FeSO 4 7H 2 O were purchased from Beijing Chemical Works. RuCl 3 3H 2 O was purchased from Sigma-Aldrich Chemical Reagent Co., Ltd. K 2 B 4 O 7 4H 2 O, KOH, KH 2 PO 4 and K 2 HPO 4 were provided by Chengdu Kelon Chemical Reagent Factory. The water used throughout all experiments was purified through a Millipore system. All the reagents and chemicals were used as received without further purification. Preparation of CoFe-LDH NA/TM, CoFe-Bi NA/TM and CoFe-Bi@CoFe-LDH NA/TM: CoFe layer double hydroxide nanoarray on Ti mesh (CoFe-LDH NA/TM) was prepared using a facile electrosynthesis method. Ti mesh (10 mm 40 mm) was pretreated with 2 M HCl solution, absolute ethanol, acetone and deionized water to ensure a clean surface. The electrodeposition solution composed of Co(NO 3 ) 2 6H 2 O (7.5 mmol), FeSO 4 7H 2 O (7.5 mmol) and 50 ml distilled water. The deposition was performed in a three-electrode system by a CHI 660E electrochemicalanalyzer (CH Instruments, Inc. Shanghai), using a piece of prepared clean TM as the working electrode, graphite rod as the counter electrode, and Hg/Hg 2 Cl 2 (SCE) as the reference electrode, respectively. The potentiostatic deposition was carried out at a potential of -1.0 V with a time of 300 s. Then, the resulting CoFe-LDH nanoarray was taken out and rinsed thoroughly with ethanol and distilled water for several times and dried at 60 C for 2 h in circulation oven. To obtain CoFe-LDH@CoFe-Bi NA/TM, the CoFe-LDH as the working electrode performed by cyclic voltammetry in 0.1 M K-Bi (ph 9.2) until the current density leveled off, with the graphite rod as the counter electrode and SCE as the reference electrode. CoFe-Bi NA/TM was synthesized according to previous work, 1 The sample was taken out and washed with ultrapure water and ethanol several times and then dried at 60 C for 2 h. The loading of CoFe-LDH@CoFe-Bi on TM was weighed at 1.42 mg cm -2. Synthesis of RuO 2 and RuO 2 /TM: RuO 2 was prepared as follows. Briefly, 2.61 g RuCl 3 3H 2 O and 1.0 ml KOH (1M) were added into 100 ml distilled water and S3

4 stirred for 45 min at 100 C. Then the above solution was centrifuged for 10 minutes and filtered. The precipitates were collected and washed with water several times. Finally, the product was dried at 80 C overnight and then annealed at 300 C in air atmosphere for 3 h. The as-prepared RuO 2 powder (0.01 g) was dispersed into a solution of Nafion, ethanol and water with a volume ratio of 10/250/250 via sonication, and deposited onto TM with a loading of 1.42 mg cm -2. Characterization: Powder X-ray diffraction (XRD) patterns were performed using a RigakuD/MAX 2550 diffractometer with Cu Kα radiation (λ= Å). Scanning electron microscope (SEM) measurements were recorded on a XL30 ESEM FEG scanning electron microscope at an accelerating voltage of 20 kv. Transmission electron microscopy (TEM) images were collected on a HITACHI H-8100 electron microscopy (Hitachi, Tokyo, Japan) operated at 200 kv. X-ray photoelectron spectroscopy (XPS) data of the samples was collected on an ESCALABMK II x-ray photoelectron spectrometer using Mg as the exciting source. Electrochemical measurements: Electrochemical measurements were performed with a CHI 660E electrochemical analyzer (CH Instruments, Inc., Shanghai) in a standard three-electrode system. CoFe-LDH@CoFe-Bi NA/TM was used as the working electrode. A graphite rod and a SCE were used as the counter electrode and the reference electrode, respectively. The temperature of solution was kept at 25 C for all the measurements via the adjustment of air condition and heating support, which ensured the variation of diffusion coefficient below 1%. The potentials reported in this work were calibrated to RHE other than especially explained, using the following equation: E (RHE) = E (SCE) + ( ph) V. S4

5 Figure S1 Cross-section SEM image for NA/TM. S5

6 Figure S2 HRTEM image for after water oxidation electrocatalysis. S6

7 Figure S3 EDX spectrum for S7

8 Figure S4 Selected area electron diffraction patterns of (a) CoFe-LDH and (b) S8

9 Figure S5 XPS survey spectrum for S9

10 Figure S6 SEM image for NA/TM after stability test for 50 h. S10

11 Figure S7 (a) LSV curves of NA/TM, CoFe-Bi NA/TM and CoFe-LDH NA/TM in 0.1 M K-Bi. (b) LSV curves of CoFe-Bi@CoFe-LDH NA/TM in 1.0 M KOH, 0.1 M K-Bi and 0.1 M PBS. S11

12 Figure S8 CVs for (a) NA/TM and (b) bare TM in the non-faradaic capacitance current range at scan rates of 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 mv s -1. Corresponding capacitive currents at 1.09 V vs. RHE as a function of scan rate for (c) CoFe-Bi@CoFe-LDH NA/TM and (d) bare TM in 0.1 M K-Bi. S12

13 Figure S9 Plot of TOF vs. potential for NA/TM. S13

14 Table S1 Comparison of OER performance for NA/TM with other non-noble-metal electrocatalysts in benign media. Catalyst j (ma cm 2 ) η (mv) Electrolyte Ref. CoFe-LDH@CoFe-Bi NA/TM M K-Bi M K-Bi M K-Bi This work Co-Bi film/gc M K-Bi 1 Co-Pi NA/Ti M PBS 2 Co-Pi/ITO M PBS 3 Fe-Bi film M BBS 4 Cu-Bi/FTO M BBS 5 CuO/FTO M KBi 6 Ni-Bi film/fto M K-Bi 7 NiO x -Bi M K-Bi 8 NiO x -Fe-Bi M K-Bi 8 Co 3 O 4 nanorod M K-Bi 9 Co 3 O 4 /MWNTs M PBS 10 Fe-Ci/FTO M CBS 11 Fe-based film M PBS 12 FeOOH/ITO M Bi 13 NiFe-LDH@NiFe-B i /CC M K-Bi 14 Ni-Pi-Bi/CC M K-Bi 15 Fe-Pi-Bi/CC M K-Bi 16 Ni-B i /CC M K-Bi 17 Co-Bi/Ti M K-B i 18 Fe-Co 3 O M K-Bi 19 CNCNT M PBS 20 Co-OEC/Ni M K-Pi 21 S14

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