Electronic Supplementary Material Reduced graphene oxide-supported CoP nanocrystals confined in porous nitrogen-doped carbon nanowire for highly enhanced lithium/sodium storage and hydrogen evolution reaction Xiaojun Zhao, Dan Luo, Yan Wang, and Zhi-Hong Liu ( ) Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an 710062, China Supporting information to https://doi.org/10.1007/s12274-019-2529-y EXPERIMENTAL SECTION All reagents in these experiments were of analytical purity and used after purchase without further processing. Synthesis of graphene oxide (GO) GO was prepared through the oxidation of natural flake graphite by using a modified Hummers’ method [S1]. Subsequently, it was kept in a drying oven for subsequent steps. Synthesis of CoP@NC/rGO nanocomposite The CoP@NC/rGO nanocomposite was synthesized via two steps including the synthesis of Co-MOF/rGO and phosphidation process. In detail, 30 mg of GO was dispersed in 20 mL of N, N-dimethylformamide (DMF) under ultrasonication for 4 h. Then, 2 mmol of Co(NO3)2·6H2O were firstly mixed with of the as-prepared GO/DMF suspension under magnetic stirring (denoted as Solution A). Subsequently, 2 mmol of 4, 4-bipyridine and 2 mmol of trimesic acid were added to the 20 mL of DMF and stirred until the 4, 4-bipyridine and trimesic acid were completely dissolved (denoted as Solution B). The Solution B was subsequently poured into Solution A, and the as-obtained mixture solution was vigorously stirred at room temperature for 30 min. Then, the resulting mixture were poured into a Teflon-lined stainless-steel autoclave (50 mL) and placed in an oven maintaining 120 °C for 6 h. The collected precipitates were washed with DMF and absolute ethanol via centrifugation, followed by drying at 60 o C overnight under vacuum. To obtain CoP@NC/rGO nanocomposite, 30 mg of as-collected composites were put in a long porcelain boat with 450 mg of NaH2PO2·H2O at up zone. Then the porcelain boat was placed into a furnace and calcined at 450 °C for 2 h under Ar flow by tuning the heating rate of 2 °C min -1 , which was denoted as CoP@NC/rGO. For comparison, CoP@NC and NC/rGO were fabricated by using the same preparation procedure without addition of GO and Co(NO3)2·6H2O, respectively. Material Characterization The crystallographic information structure of the samples was characterized by Bruker D8 ADVANCE X-ray powder diffractometer equipped with a Cu Kα radiation of 1.5406 Å in a step of 0.02° per second in the 2θ ranging from 10-80 o . FESEM was used to characterize the surface morphology with Hitachi SU-8020 spectrophotometer. TEM and HRTEM images were obtained using a Tecnai G2 F20 (FEI) microscope. The surface compositions were analyzed via X-ray photoelectron spectroscopy (XPS) on an Axis Ultra XPS system (Axis Ultra DLD, Kratos) with a monochromatic Al Kα X-ray source (1486.6 eV). Raman spectra were recorded on a Raman spectrometer (Via-Reflex, Renishaw, UK) with laser excitation wavelength of 532 nm. Brunauer-Emmett-Teller specific surface area (SBET) and the pore size distribution were calculated from N2 adsorption/desorption isotherms measured at 77 K on a Micromeritics 3Flex apparatus, respectively. Electrochemical characterization Li/Na-ion Batteries Measurements. The battery performance of as-prepared products for Li/Na-ion cells was carried out at room temperature based on a 2025 coin-type configuration. For the preparation of the working electrode, the mixture of as-obtained samples, carbon black (Super-P-Li), and polyvinylidene fluoride (PVDF) with a weight ratio of 8:1:1 was ground in a mortar with N-methy1-2-pyrrolidone (NMP) as solvent for making a slurry. The slurry mixture was then pasting on Ni foil (14 mm in diameter) and subsequently dried in vacuum for 12 h (80 °C) to remove NMP for test. The mass loading of the active material on each disk was ~1.5 mg cm –2 . A Celgard 2400 membrane was used as the separator for all coin cells. For Li-ion batteries, the counter/reference electrode was metallic Li foil and the electrolyte was composed of 1 M LiPF6 in dimethyl carbonate/diethyl carbonate/ethylene carbonate (EC) (v/v/v, 1:1:1). While for Na-ion batteries, the working electrodes were replaced by Na foil, and the electrolyte was 1 M NaClO4 in a mixture of propylene carbonate/EC (v/v, 1:1). GDC tests were performed with a LAND-CT2001A battery testing system in the potential range of 0.005 -3.0 V. The CHI 760E electrochemical workstation (Chenhua, Shanghai) was used to measure the CV and EIS properties in the frequency range from 100 kHz to 10 mHz. Electrocatalysis for HER. HER tests of various catalysts were evaluated in a conventional three-electrode system in the N2 saturated 0.5 M H2SO4 solution, in which the catalysts CoP@NC/rGO electrode, saturated calomel electrode (SCE), and graphite rod served as the working Address correspondence to [email protected]
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Electronic Supplementary Material
Reduced graphene oxide-supported CoP nanocrystals confined in porous nitrogen-doped carbon nanowire for highly enhanced lithium/sodium storage and hydrogen evolution reaction Xiaojun Zhao, Dan Luo, Yan Wang, and Zhi-Hong Liu ()
Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an 710062, China Supporting information to https://doi.org/10.1007/s12274-019-2529-y
EXPERIMENTAL SECTION All reagents in these experiments were of analytical purity and used after purchase without further processing.
Synthesis of graphene oxide (GO)
GO was prepared through the oxidation of natural flake graphite by using a modified Hummers’ method [S1]. Subsequently, it was kept in a drying oven for subsequent steps.
Synthesis of CoP@NC/rGO nanocomposite
The CoP@NC/rGO nanocomposite was synthesized via two steps including the synthesis of Co-MOF/rGO and phosphidation process. In detail, 30 mg of GO was dispersed in 20 mL of N, N-dimethylformamide (DMF) under ultrasonication for 4 h. Then, 2 mmol of Co(NO3)2·6H2O were firstly mixed with of the as-prepared GO/DMF suspension under magnetic stirring (denoted as Solution A). Subsequently, 2 mmol of 4, 4-bipyridine and 2 mmol of trimesic acid were added to the 20 mL of DMF and stirred until the 4, 4-bipyridine and trimesic acid were completely dissolved (denoted as Solution B). The Solution B was subsequently poured into Solution A, and the as-obtained mixture solution was vigorously stirred at room temperature for 30 min. Then, the resulting mixture were poured into a Teflon-lined stainless-steel autoclave (50 mL) and placed in an oven maintaining 120 °C for 6 h. The collected precipitates were washed with DMF and absolute ethanol via centrifugation, followed by drying at 60 oC overnight under vacuum. To obtain CoP@NC/rGO nanocomposite, 30 mg of as-collected composites were put in a long porcelain boat with 450 mg of NaH2PO2·H2O at up zone. Then the porcelain boat was placed into a furnace and calcined at 450 °C for 2 h under Ar flow by tuning the heating rate of 2 °C min-1, which was denoted as CoP@NC/rGO. For comparison, CoP@NC and NC/rGO were fabricated by using the same preparation procedure without addition of GO and Co(NO3)2·6H2O, respectively.
Material Characterization
The crystallographic information structure of the samples was characterized by Bruker D8 ADVANCE X-ray powder diffractometer equipped with a Cu Kα radiation of 1.5406 Å in a step of 0.02° per second in the 2θ ranging from 10-80o. FESEM was used to characterize the surface morphology with Hitachi SU-8020 spectrophotometer. TEM and HRTEM images were obtained using a Tecnai G2 F20 (FEI) microscope. The surface compositions were analyzed via X-ray photoelectron spectroscopy (XPS) on an Axis Ultra XPS system (Axis Ultra DLD, Kratos) with a monochromatic Al Kα X-ray source (1486.6 eV). Raman spectra were recorded on a Raman spectrometer (Via-Reflex, Renishaw, UK) with laser excitation wavelength of 532 nm. Brunauer-Emmett-Teller specific surface area (SBET) and the pore size distribution were calculated from N2 adsorption/desorption isotherms measured at 77 K on a Micromeritics 3Flex apparatus, respectively.
Electrochemical characterization
Li/Na-ion Batteries Measurements. The battery performance of as-prepared products for Li/Na-ion cells was carried out at room temperature based on a 2025 coin-type configuration. For the preparation of the working electrode, the mixture of as-obtained samples, carbon black (Super-P-Li), and polyvinylidene fluoride (PVDF) with a weight ratio of 8:1:1 was ground in a mortar with N-methy1-2-pyrrolidone (NMP) as solvent for making a slurry. The slurry mixture was then pasting on Ni foil (14 mm in diameter) and subsequently dried in vacuum for 12 h (80 °C) to remove NMP for test. The mass loading of the active material on each disk was ~1.5 mg cm–2. A Celgard 2400 membrane was used as the separator for all coin cells. For Li-ion batteries, the counter/reference electrode was metallic Li foil and the electrolyte was composed of 1 M LiPF6 in dimethyl carbonate/diethyl carbonate/ethylene carbonate (EC) (v/v/v, 1:1:1). While for Na-ion batteries, the working electrodes were replaced by Na foil, and the electrolyte was 1 M NaClO4 in a mixture of propylene carbonate/EC (v/v, 1:1). GDC tests were performed with a LAND-CT2001A battery testing system in the potential range of 0.005 -3.0 V. The CHI 760E electrochemical workstation (Chenhua, Shanghai) was used to measure the CV and EIS properties in the frequency range from 100 kHz to 10 mHz. Electrocatalysis for HER. HER tests of various catalysts were evaluated in a conventional three-electrode system in the N2 saturated 0.5 M H2SO4 solution, in which the catalysts CoP@NC/rGO electrode, saturated calomel electrode (SCE), and graphite rod served as the working
Address correspondence to [email protected]
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electrode, reference electrode, and the counter electrode, respectively. The working electrode was prepared by loading catalyst sample film on glass carbon electrode (GCE) (d = 3 mm, S = 0.07065 cm2). First, the catalyst inks were prepared by dispersing 4 mg of catalyst and 20 μL of 5 wt % Nafion solution in 980 μL of 1:1 v/v water/ethanol mixed solvent by at least 40 min sonication to form a homogeneous dispersion. Next, 4 μL of the catalyst ink was loaded onto a GCE. The HER activity was evaluated by LSV were performed with a scan rate of 5 mV s-1 after 95% iR-compensation through the positive feedback model, and the CVs were recorded as following between 0.1 and 0.3 V versus RHE with various scan rates (10-200 mV s-1). The long-term stability was tested at overpotential of current densities of 10 mA cm-2. All the electrochemical data were calibrated with respect to reversible RHE based on following equation: ERHE = ESCE + (0.242 + 0.0591 pH) V. For the electrochemical measurements, the CHI 760E electrochemical analyzer was used.
2. FIGURES and TABLES
Figure S1 (a) Coordination environments of Co2+ ions in the asymmetric units of Co-MOF (Co(HBTC)(4,4’-bipy)· 3DMF), and (b) PXRD patterns of Co-MOF, Co-MOF/rGO and simulated single crystal pattern.
Figure S2 TGA curves of Co-MOF and Co-MOF/rGO using TGA/DSC 3+ (Germany) in N2 atmosphere from 25 to 600 °C with a heating rate of 10 °C min-1, respectively. The fully pyrolysis of the Co-MOF is observed at around 450 °C. TGA curve for the Co-MOF/rGO hybrids is similar to that of the Co-MOF. Importantly, the hybrids show higher thermal stability compared to the Co-MOF, which is likely due to the chemical bonding between the Co-MOF and rGO substrate. On the basis of TGA analysis, 450 °C is chosen as the calcinating temperature to obtain the final products.
Figure S3 TEM image of CoP@NC/rGO hybrids.
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Figure S4 SEM images of (a) Co-MOF, (b, c) CoP@NC, and (d) NC/rGO, respectively.
Figure S5 Raman spectra of NC/rGO, CoP@NC, and CoP@NC/rGO hybrids.
Figure S6 XPS spectra of CoP@NC/rGO nanocomposite: (a) broad scan spectrum, (b) N 1s and (c) C 1s, respectively.
Figure S7 Cyclic voltammetry of CoP@NC/rGO electrode for LIBs at a scan rate of 0.1 mV s-1 in a voltage range of 0 - 3.0 V.
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Figure S8 (a, b) SEM images of CoP@NC electrode for LIBs after 100 cycles.
Figure S9 SEM and elemental mappings of Co, P, N, C, F and Ni in CoP@NC/rGO electrode for LIBs after 100 cycles.
Figure S10 (a) Nyquist plots of NC/rGO, CoP@NC, and CoP@NC/rGO nanocomposites after 1st cycling, and (b) the equivalent circuit model.
Table S1 Electrochemical impedance parameters of as-obtained CoP-based materials for LIBs from equivalent circuit fitting of experimental data.
Sample Cycle number Rs/Ohm Rf/Ohm Rct/Ohm
CoP@NC 1st cycle 5.97 34.18 92.61
1st cycle 4.21 19.28 50.39
150th cycle 4.25 23.03 55.58
CoP@NC/rGO
300th cycle 4.63 25.62 59.51
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Figure S11 (a) CV curves and (b) the initial three cycles GDC profiles of CoP@NC/rGO electrode for NIBs.
Figure S12 Sodium storage performance comparison of specific capacities of the CoP@NC/rGO nanocomposite with other CoP-C/graphene materials reported in the literatures.
Figure S13 The Nyquist plots of CoP@NC/rGO electrode in LIBs and NIBs.
Figure S14 Comparison of HER performance of CoP@NC/rGO electrode with previously reported CoP-based composites at a current density of 10 mA·cm-2 in 0.5 M H2SO4.
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Figure S15 CVs performed at various scan rates in the region of 0.10-0.20 V at different sweep rates from 10 to 200 mV s-1 versus RHE for (a) CoP@NC/rGO and (b) CoP@NC electrocatalysts, and (c) the Cdl value of CoP@NC/rGO (3.55 mF) and CoP@NC (1.62 mF), respectively.
Figure S16 (a) Mass-normalized and (b) ECSA-normalized initial LSV polarization curves of the CoP@NC and CoP@NC/rGO electrocatalysts from Fig. 8a.
References [S1] Zhao, X., Wang, H., Zhai, G., Wang, G. Facile Assembly of 3D Porous Reduced Graphene Oxide/Ultrathin MnO2 Nanosheets-S Aerogels as Efficient
Polysulfide Adsorption Sites for High-Performance Lithium-Sulfur Batteries. Chemistry-A European Journal, 2017, 23(29), 7037-7045. [S2] Li, J., Shi, L., Gao, J., Zhang, G. General One-Pot Synthesis of Transition-Metal Phosphide/Nitrogen-Doped Carbon Hybrid Nanosheets as Ultrastable Anodes
for Sodium-Ion Batteries. Chemistry-A European Journal, 2018, 24(6), 1253-1258. [S3] Zhang, K., Park, M., Zhang, J., Lee, G. H., Shin, J., Kang, Y. M. Cobalt Phosphide nanoparticles Embedded in nitrogen-doped carbon nanosheets: Promising
Anode Material with High Rate Capability and Long Cycle Life for Sodium-ion batteries. Nano Research, 2017, 10(12), 4337-4350. [S4] Jin, R., Li, X., Sun, Y., Shan, H., Fan, L., Li, D., Sun, X. Metal-organic frameworks-derived Co2P@NC@rGO with Dual Protection Layers for Improved
Sodium Storage. ACS applied materials & interfaces, 2018, 10(17), 14641-14648.
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