SUPPORTING INFORMATION

Transcription

1 SUPPORTING INFORMATION Ultrasmall Ni/NiO Nanoclusters on Thiol Functionalized and Exfoliated Graphene Oxide Nanosheets for Durable Oxygen Evolution Reaction Akhtar Munir, Tanveer-ul-Haq, Ahsanulhaq Qurashi, Habib ur Rehman, Anwar-Ul-Hamid, and Irshad Hussain*, Department of Chemistry & Chemical Engineering, SBA School of Science & Engineering, Lahore University of Management Sciences (LUMS), DHA, Lahore, 54792, Pakistan Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Center of Engineering Research, King Fahad University of Petroleum and Minerals. Dhahran 31261, Saudi Arabia Corresponding Author * (Irshad Hussain) S-1

2 . Scheme S1. Schematic illustration of thiolation of GO and loading of Ni/NiO NCs. From 1 to 4 are the different steps taking place during functionalization, R = carbon network of the graphene oxide. S-2

3 Figure S1. FT-IR spectrum of GO, G-SH and Figure S2. Raman spectra of (a) G-SH (b) GO (c) S-3

4 a b 5 µm 1um c d e f b a Figure S3. (a) SEM image of GO sheets, (b) Electron image and corresponding elemental mapping of GO, inset is the EDX spectrum of GO (c) Carbon (d) Oxygen (e) Cupper (f) Aluminum. (Al and Cu come from the stub used for the sample holding). b S-4

5 a b b 500 nm c d e Figure S4. (a) SEM image of G-SH (b) EDX spectrum of G-SH and corresponding elemental mapping of G-SH, (c) Carbon (d) Oxygen (e) Sulfur. a b c d Figure S5. (a) EDX spectrum of Ni/NiO@G-SH and elemental mapping of (b) Sulfur (c) Carbon (d) Nickel S-5

6 a b 200 nm 500 nm c d e Figure S6. (a) SEM image of NiO@GO (b) Electron image of NiO@GO and corresponding elemental mapping, (c) Carbon (d) Oxygen (e) Nickel. Figure S7. TEM image of G-SH. S-6

7 Figure S8. HRTEM image of Figure S9. Selected area electron diffraction pattern (SAED) of S-7

8 Figure S10. XPS analysis: C 1s core level spectrum of Ni/NiO@G-SH after etching. Figure S11. (a) XPS core spectrum of oxygen after etching Ni/NiO@G-SH (b) Oxygen 1s core level spectrum of Ni/NiO@G-SH nanohybrid in the selected region after etching. S-8

9 Figure S12. XPS core level spectrum of S 2p after etching Ni/NiO@G-SH nanohybrid. Figure S13. Linear swap voltammetry (LSV) of Ni/NiO@G- SH in 0.1M KOH solution with scan rate of 5 mv/s. S-9

10 Figure S14. Polarization curve of before and after base purification in 0.1M KOH solution with scan rate of 5 mv/s. Figure S15. Electrochemical impedance spectroscopy: Nyquist plots of Ni/NiO@G-SH, IrO 2, NiO@GO, and G-SH in the frequency range of 0.1Hz to 1MHz at 1.6 V vs RHE in 0.1M KOH. S-10

11 Figure S16. Chronoamperometry of and at 1.6 V in 0.1M KOH without ir correction. Figure S17. (a) Polarization curve of Ni/NiO@G-SH before and after long term (85 h) stability test in 0.1M KOH with scan rate of 5 mv/s. (b) EIS before and after 85 h stability. S-11

12 a b c Figure S18. Area under the curve of the reduction peak of Ni +2/+3 redox couple. At various potential window (a) to V) (b) to V (c) to V. An optimum range (1.191 to V, Figure a) was used for calculation. Calculation of electrochemical parameters E RHE = E exp *pH + E Ag/Agcl (ph, 13 for 0.1M KOH) (1) RHE is the potential of reversible hydrogen electrode, E exp is the experimental potential and E Ag/AgCl is the potential of reference electrode Tafel equation ɳ = b log j + a (2) S-12

13 ɳ is the overpotential, b is the Tafel slope and j is the current density Mass activity (A/g) = j/m (3) J is the current at particular potential and m is the loaded mass/cm 2 (Figure 6b) (a) Determination of Surface Concentration of Ni from CV Area under the curve of the reduction peak in the redox couple of Ni +3 to Ni +2 = V ma Hence, charge is = V ma / 0.02 Vs-1 = ma s or = A s i.e., = Coulombs (since q =It) Then, no. of electrons = C/ C = electron Now, divide by the number of electron transferred in the redox reaction which is 1 here. = /1 = atoms Area under the curve of reduction peak used for these calculation is shown in the Figure S18. (b) Determination of TOF from the integrated OER polarization curve TOF= i NA/A F n ᴦ (4) Where, i = current in Ampere NA= Avogadro number A = Geometrical surface area of the electrode (1 cm 2 ) F = Faraday constant n = Number of electrons ᴦ = Surface concentration of atoms TOF1.46V = [(0.002*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 3.60 s -1 TOF1.48V = [(0.004*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 7.21 s -1 S-13

14 TOF1.50V = [(0.0055*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 9.92s -1 TOF1.52V = [(0.010*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 18 s -1 TOF1.54V = [( *10 23 )] / [(1)*(96485)*(4)*( ) = 27.0 s -1 TOF1.56V = [(0.028*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 50.1 s -1 TOF1.58V = [(0.040*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = s -1 TOF1.60V = [(0.050*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = 90.1 s -1 TOF1.62V = [(0.062*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = s -1 TOF1.64V = [(0.072*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = TOF1.66V = [(0.088*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = s -1 TOF1.68V = [(0.100*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = s -1 TOF1.70V = [(0.120*6.022*10 23 )] / [(1)*(96485)*(4)*( ) = s -1 TOF1.72 V = [(0.136*6.022*10 23 )] / [(1)*(96485)*(4)*( = s -1 S-14

15 (c) Exchange current density from EIS Exchange current density (i ex ) = RT/nFӨ (5) R is universal gas constant (8.314 j/k.mol), T is the reaction temperature, n is the number of electrons transfer (4 eˉ), Ө is the resistance calculated from EIS Ni/NiO@G-SH J/K. mol * 298 K 4 * Cmol -1 * 2.5 Ω * 1 cm 2 = 2.6 ma/cm 2 IrO J/K. mol * 298 K 4 * Cmol -1 * 9 Ω * 1 cm 2 = 0.71 ma/cm J/K. mol * 298 K 4 * Cmol -1 * 20 Ω * 1 cm 2 = 0.32 macm 2 G-SH J/K. mol * 298 K 4 * Cmol -1 *32Ω * 1 cm 2 = 0.20 macm 2 (d) Electrochemical active surface area (EASA) Double layer charging current (i c ) = v C DL (6) ν is the scan rate and C DL is the double layer capacitance equal to the slope of plot of ν vs current density. EASA = C DL /Cs (7) S-15

16 where Cs is the specific capacitance of a sample under the specific condition of electrolyte and C DL is the double layer capacitance in the non-faradic region of voltammogram. For Ni the reported value of Cs varies from mf to mf in alkaline conditions. 1 Hence, we chose an average value (0.040 mf) to get the average value of EASA of our catalyst). Ni/NiO@G-SH NiO@GO G-SH = 15.4 mfcm 2 / mf 385 cm 2 = 10.8 mfcm 2 / cm 2 = 5.5 mfcm 2 / cm 2 S-16

17 Figure S19. Polarization curve of (a) (b) (c) IrO 2 (d) G-SH at different scan rate (5 to 25 mv/s) in the potential window of 1.07 to 1.17 V in 0.1 M KOH. S-17

18 Table S1. Average current density (j) from the polarization curves and C DL calculation Electrocatalyst Potential (V) Mean value of j at different scan rate (mv/s) C DL V1 V2 V (mf/cm 2 ) Ni/NiO@G-SH IrO NiO@GO G-SH j: current density (ma/cm 2 ), V1, V2, V3: Different potential, C DL : Double layer capacitance, mf: milli-farad Figure S20. Plots of average capacitive current (J) as a function of scan rate. slope = double layer capacitance (C DL ). S-18

19 Table S2. Comparison of OER activity of various catalyst with this work SR # Electrocatalyst Overpotential Tafel Stability 10mAcm -2 Slope (mv/dec) (hours) 1 Ni/NiO@G-SH This work 2 Colloidal NiO NPs NiSe NW NiO@TiO mv Co-N/GF Ni 3 C/C Ni NPs-N doped graphene 8 NiO Ni/NF Ni 6 (PET) NiSe@NiOx α-ni(oh) NiCO@NC (N-doped carbon nanofiber) 13 Co@GO QDts s NiFe LDH cycles 15 NiO-WS NW: nanowire, NPs: nanoparticles, GF: graphite foam, PA: phosphorus and aluminum, NF: Nickel foam, PET: 2-phenylethanthiol, QDts: Quantum dots, LDH: Layer double hydroxide, WS: Tungsten sheets S-19

20 References (1) McCrory, C. C.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J. Am. Chem. Soc. 2013, 135, (2) Fominykh, K.; Feckl, J. M.; Sicklinger, J.; Döblinger, M.; Böcklein, S.; Ziegler, J.; Peter, L.; Rathousky, J.; Scheidt, E. W.; Bein, T. Ultrasmall dispersible crystalline nickel oxide nanoparticles as high performance catalysts for electrochemical water splitting. Adv. Funct. Mater. 2014, 24, (3) Li, Y.; Yan, D.; Zou, Y.; Xie, C.; Wang, Y.; Zhang, Y.; Wang, S. Rapidly engineering the electronic properties and morphological structure of NiSe nanowires for the oxygen evolution reaction. J. Mater. Chem. A. 2017, 5, , (4) Zhao, Y.; Jia, X.; Chen, G.; Shang, L.; Waterhouse, G. I. N.; Wu, L.-Z.; Tung, C.-H.; O Hare, D.; Zhang, T. Ultrafine NiO Nanosheets Stabilized by TiO2 from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst. J. Am. Chem. Soc. 2016, 138, (5) Tong, Y.; Yu, X.; Wang, H.; Yao, B.; Li, C.; Shi, G. Trace Level Co N Doped Graphite Foams as High-Performance Self-Standing Electrocatalytic Electrodes for Hydrogen and Oxygen Evolution. ACS Catal. 2018, 8, (6) Xu, K.; Ding, H.; Lv, H.; Chen, P.; Lu, X.; Cheng, H.; Zhou, T.; Liu, S.; Wu, X.; Wu, C. Dual Electrical Behavior Regulation on Electrocatalysts Realizing Enhanced Electrochemical Water Oxidation. Adv. Mater. 2016, 28, (7) Xu, Y.; Tu, W.; Zhang, B.; Yin, S.; Huang, Y.; Kraft, M.; Xu, R. Nickel Nanoparticles Encapsulated in Few Layer Nitrogen Doped Graphene Derived from Metal Organic Frameworks as Efficient Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Mater. 2017, 29, (8) Yue, Z.; Zhu, W.; Li, Y.; Wei, Z.; Hu, N.; Suo, Y.; Wang, J. Surface Engineering of a Nickel Oxide Nickel Hybrid Nanoarray as a Versatile Catalyst for Both Superior Water and Urea Oxidation. Inorg. Chem. 2018, 57, (9) Kauffman, D. R.; Alfonso, D.; Tafen, D. N.; Lekse, J.; Wang, C.; Deng, X.; Lee, J.; Jang, H.; Lee, J.-s.; Kumar, S. Electrocatalytic oxygen evolution with an atomically precise nickel catalyst. ACS Catal. 2016, 6, (10) Gao, R.; Li, G.-D.; Hu, J.; Wu, Y.; Lian, X.; Wang, D.; Zou, X. In situ electrochemical formation of NiSe/NiOx core/shell nano-electrocatalysts for superior oxygen evolution activity. Catal. Sci. Technol. 2016, 6, (11) Gao, M.; Sheng, W.; Zhuang, Z.; Fang, Q.; Gu, S.; Jiang, J.; Yan, Y. Efficient water oxidation using nanostructured α-nickel-hydroxide as an electrocatalyst. J. Am. Chem. Soc. 2014, 136, (12) Fu, Y.; Yu, H. Y.; Jiang, C.; Zhang, T. H.; Zhan, R.; Li, X.; Li, J. F.; Tian, J. H.; Yang, R. NiCo Alloy Nanoparticles Decorated on N Doped Carbon Nanofibers as Highly Active and Durable Oxygen Electrocatalyst. Adv. Funct. Mater.2018, 28, S-20

21 (13) Govindhan, M.; Mao, B.; Chen, A. Novel cobalt quantum dot/graphene nanocomposites as highly efficient electrocatalysts for water splitting. Nanoscale 2016, 8, (14) Wang, Y.; Qiao, M.; Li, Y.; Wang, S. Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction. Small 2018, 14, (15) Wang, D.; Li, Q.; Han, C.; Xing, Z.; Yang, X. When Ni Meets WS2 Nanosheet Array: A Highly Efficient and Ultrastable Electrocatalyst for Overall Water Splitting. ACS Cent. Sci. 2017, 4, S-21