Supporting Information

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1 Copyright WILEY VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information for Adv. Funct. Mater., DOI: /adfm Ultrahigh-Performance Pseudocapacitor Electrodes Based on Transition Metal Phosphide Nanosheets Array via Phosphorization: A General and Effective Approach Kai Zhou, Weijia Zhou,* Linjing Yang, Jia Lu, Shuang Cheng, Wenjie Mai, Zhenghua Tang, Ligui Li, and Shaowei Chen*

2 Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information Ultrahigh-performance pseudocapacitor electrodes based on transition metal phosphide nanosheets array via phosphorization: a general and effective approach Kai Zhou, Weijia Zhou*, Linjing Yang, Jia Lu, Shuang Cheng, Wenjie Mai, Zhenghua Tang, Ligui Li, Shaowei Chen* K. Zhou, Dr. W. J. Zhou, L. J. Yang, J. Lu, Dr. S. Cheng, Prof. Z. H. Tang, Prof. L. G. Li, Prof. S. W. Chen New Energy Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou Higher Education Mega Center, Guangzhou, Guangdong , China eszhouwj@scut.edu.cn; shaowei@ucsc.edu Prof. W. J. Mai Department of Physics and Siyuan Laboratory, Jinan University, Guangzhou, Guangdong , China Prof. S. W. Chen Department of Chemistry and Biochemistry, University of California, 1156 High Street, Santa Cruz, California 95064, USA Synthesis of Ni Foam Supported Co(OH)F Nanosheets (Co(OH)F/NF) The Ni Foam was then subject to a hydrothermal process to grow Co(OH)F nanosheets (Co(OH)F/NF) on the surface. In a typical procedure, Co(NO) 2 6H 2 O (2 mmol), NH 4 F (8 mmol) and CO(NH 2 ) 2 (10 mmol) were dissolved in DI water (36 ml) to form a pink solution. The solution was transferred to a 40 ml Teflon-lined stainless autoclave. A piece of the pre-treated Ni foam was put in the autoclave. The autoclave was then sealed and heated at 100 C for 6 h. After it was cooled down to room temperature, the Ni foam was washed with DI water and ethanol several times and dried in air. The weight of Co(OH)F nanosheets was about 3.2 mg per 1 cm 1 cm of the Ni foam by subtracting the weight before deposition

3 from the weight after deposition. Synthesis of Ni Foam Supported MnO 2 Nanosheets (MnO 2 /NF) The Ni Foam was then subject to a hydrothermal process to grow MnO 2 nanosheets (MnO 2 /NF) on the surface. In a typical procedure, KMnO 4 (60 mmol) was dissolved in DI water (30 ml). The solution was transferred to a 40 ml Teflon-lined stainless autoclave. A piece of the pre-treated Ni foam was put in the autoclave. The autoclave was then sealed and heated at 130 C for 6 h. After it was cooled down to room temperature, the Ni foam was washed with DI water and ethanol several times and dried in air. The weight of MnO 2 nanosheets was about 2.6 mg per 1 cm 1 cm of the Ni foam by subtracting the weight before deposition from the weight after deposition. Synthesis of Fe 2 O 3 powder FeCl 3 6H 2 O was heated to 350 C at a heating rate of 5 C min 1 for 2 h under an Air flow. Synthesis of Ni Foam Supported Co 2 P Nanosheets (Co 2 P/NF) The synthesis of Co 2 P/NF was carried out in a closed porcelain crucible placed at the middle of a horizontal tube furnace. NaH 2 PO 2 H 2 O powders (10.0 mg) were placed at the upstream side of the porcelain crucible and the as-grown Co(OH)F/NF at the opposite end. The samples were heated to 300 C at a heating rate of 5 C min 1 for 2 h under an Ar flow. Co 2 P/NF was collected after the furnace was cooled to ambient temperature. The mass of the Co 2 P nanosheets on Ni foam was determined by subtracting the weight of Ni foam from the weight of the Co 2 P/NF. On average, 2.5 mg of Co 2 P nanosheets was grown on a 1 cm 1 cm piece of Ni foam, as quantified by a high precision microbalance. Synthesis of Ni Foam Supported phosphatized MnO 2 Nanosheets (Mn-O-P/NF)

4 The synthesis of Mn-O-P/NF was carried out in a closed porcelain crucible placed at the middle of a horizontal tube furnace. NaH 2 PO 2 H 2 O powders (10.0 mg) were placed at the upstream side of the porcelain crucible and the as-grown MnO 2 /NF at the opposite end. The samples were heated to 300 C at a heating rate of 5 C min 1 for 2 h under an Ar flow. Mn-O-P/NF was collected after the furnace was cooled to ambient temperature. The mass of the Mn-O-P nanosheets on Ni foam was determined by subtracting the weight of Ni foam from the weight of the Mn-O-P/NF. On average, 3.0 mg of Mn-O-P nanosheets was grown on a 1 cm 1 cm piece of Ni foam, as quantified by a high precision microbalance. Synthesis of Fe x P powder The as-prepared Fe 2 O 3 powder (20 mg) and NaH 2 PO 2 H 2 O (100 mg) mixed together and grind to a fine powder by using a mortar. Then, the mixture was heated to 350 C at a heating rate of 5 C min 1 for 2 h under an Ar flow.

5 Figure S1. Photographs of (a) Ni foam, (b) Ni(OH) 2 NS/NF and (c) Ni 2 P NS/NF. Figure S2. XPS spectrum of O 1s electrons of Ni 2 P NS/NF. Figure S3. (a) CV curves of NF (Ni foam) and NF-P at the scan rate of 5 mv/s in 6.0 M KOH. Figure S4. XRD pattern of Ni(OH) 2 and Ni 2 P powder.

6 Figure S5. (a) CV and (b) galvanostatic charge/discharge curves of the Ni(OH) 2 powder and Ni 2 P powder electrode at the scan rate of 5 mv s 1 and the current density of 10 A g 1 in 6.0 M KOH, respectively. Figure S6. Nitrogen adsorption/desorption isotherms of Ni(OH) 2 and Ni 2 P powder. Figure S7. Area capacitances of the Ni 2 P NS/NF and Ni(OH) 2 NS/NF electrode as a function of (a) scan rate and (b) current density.

7 Figure S8. the corresponding SAED pattem of Ni 2 P nanosheet after the cycle test. Figure S9. SEM image of Ni 2 P NS/NF after the cycle test. Figure S10. CV curves of activated carbon (AC) and Ni 2 P NS/NF electrodes at a scan rate of 50 mv s 1 in 6 M KOH tested separately in three-electrode system.

8 Figure S11. (a) Galvanostatic charge/discharge curves of the Ni 2 P NS/NF//AC asymmetric supercapacitor device at different current densities. (b) Specific capacitances of the device as a function of current density. (c) EIS plots of the asymmetric supercapacitor device (the inset shows the enlarged view of the high frequency region and the equivalent circuit diagram of different elements from the EIS analysis). (d) Ragone plots of the Ni 2 P NS/NF//AC asymmetric supercapacitor. Figure S12. (a) XPS spectrum of P 2p electrons of Co 2 P NS/NF. (b) XPS spectra of Co 2p 3/2 electrons of (top curve) Co 2 P NS/NF and (bottom curve) Co(OH)F NS/NF. Black curves are experimental data and color curves are deconvolution fits. The peak centered at ev in the spectra of P 2p is ascribed to the form of metal phosphide, [1] the peak centered at ev in the spectra of Co 2p 3/2 electrons is assigned to [1, 2] the Co 2 P phase after phosphorization reaction.

9 Figure S13 SEM images of (a) MnO 2 /NF and (b) Mn-O-P/NF. (c) CV curves of MnO 2 /NF (black curve) and Mn-O-P/NF (red curve) at the scan rate of 5 mv s 1 in 6.0 M KOH. (d) Galvanostatic charge/discharge curves of the MnO 2 /NF and Mn-O-P/NF at the current density of 10 ma cm 2 in 6.0 M KOH. Figure S14. XPS spectra of (a) Mn 2p, (b) P 2p, and (c) O 1s electrons of MnO 2 /NF and Mn-O-P/NF. The specific capacitance becomes larger after the MnO 2 nanosheets grown on the surface of Ni foam (MnO 2 /NF) was treated in the presence of NaH 2 PO 2 H 2 O at 300 C under an Ar flow. The overall morphology of the MnO 2 nanosheets after phosphorization treatment (Mn-O-P/NF) is similar to the MnO 2 /NF (Figure S13a and b). XPS spectra of Mn 2p shows

10 only two peaks located at ev and ev are assigned the Mn 4+ oxidation state [3] (Figure S14a). After phosphorization treatment, the presence of phosphate phase was confirmed by the binding energy of P 2p at around ev and the binding energy of O 1s at around ev (Figure S14b and c). The specific capacitance of Mn-O-P/NF is 549 F g 1 at 5 mv s calculated from CV curve, larger than 413 F/g of MnO 2 /NF. As well, the specific capacitance of Mn-O-P/NF is 232 F g 1 at 10 ma cm 2 calculated from galvanostatic charging/discharging curve, more than 181 F g 1 of MnO 2 /NF. Figure S15. (a) XRD patterns of Fe 2 O 3 (black curve) and Fe x P (red curve). (b) CV curves of Fe 2 O 3 and Fe x P at the scan rate of 100 mv s 1 in 6.0 M KOH. Similarly, the specific capacitance can be increased to 146 mf g 1 from 32 mf g 1 at 100 mv s 1 after the Fe 2 O 3 was successfully converted to Fe x P via a phosphorization reaction (Figure S15).

11 Table S1 Comparison of electrochemical performances of Ni-based materials Materials Electrolyte Voltage Specific Mass Loading Ref. (aqueous) range [V] Capacitance [mg cm 2 ] MWCNT/amorphous Ni(OH) 2 / PEDOTPSS 1 M KOH 0~ F g 1 at 5 mv s [4] Ni(OH) 2 /CNT/NF KOH 0~ F g 1 at 4.85 [5] 1 mv s 1 Ni(OH) 2 /NF 3% KOH 0.05~ F g 1 at 0.5 [6] 4 A g 1 NiO/MWCNTs 2 M KOH 0~ F g 1 at [7] 5 ma cm 2 NiO-3D graphene 1 M NaOH 0~ F g 1 at 0.46 [8] 3 A g 1 Ni 3 S 2 / NF 6 M KOH 0~ F g [9] at 2 A g 1 Ni 3 S 2 /3DGN 3 M KOH 0.15~ F g 1 at 3.7 [10] 2 mv s 1 Ni-coated Ni 2 P 2.0 M LiOH 0~ F g 1 at ~3.0 [11] 2 A g 1 Ni 2 P/rGO 2 M KOH 0~ F g 1 [12] at 1 mv s 1 Ni2P NS/NF 6 M KOH 0.1~ F g 1 at 1.2 This work 5 mv s 1 [1] Z. Huang, Z. Chen, Z. Chen, C. Lv, M. G. Humphrey, C. Zhang, Nano Energy 2014, 9, 373. [2] E. J. Popczun, C. G. Read, C. W. Roske, N. S. Lewis, R. E. Schaak, Angew. Chem. 2014, 126, 5531.

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