Supporting Information

Transcription

1 Supporting Information Hierarchical Ultrathin Carbon Nanoflakes as Alkaline Oxygen Evolution and Acidic Hydrogen Evolution Catalyst for Efficient Water Electrolysis and Organic Decomposition Bowei Zhang, Yu Hui Lui, Anand P. S. Gaur, Bolin Chen, Xiaohui Tang, Zhiyuan Qi, and Shan Hu* Department of Mechanical Engineering, Iowa State University, Ames, Iowa 50011, USA Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA shanhu@iastate.edu S-1

2 Supplementary SEM images, electrochemical data, XPS analysis, movies, and comparison table: Figure S1. SEM images on the growth process of FeNi hydroxide micro-flower spheres after a) 6h, b) 7h, and c) 12h. The red circles in a) indicates the sphere starts to grow after 6h. Structural collapse is shown in c), the diameter of the sphere increased as well. Figure S2. OER LSV plots of FeNi-OH at different growth time. S-2

3 Figure S3. HR-STEM image of the edge part of the nanosheet. Some crystalline FeNiP clusters were trapped in the amorphous carbon shell. S-3

4 Intensity (a.u.) Figure S4. a) XPS survey spectrum and high resolution XPS spectra for b) Ni 2p, c) Fe 2p, d) P 2p, e) C 1s, and f) O 1s of FeNiP@C. I D /I G = 0.96 D G Raman shift (cm -1 ) Figure S5. Raman spectrum of the nanocarbon layer recorded from the FeNiP@C surface. S-4

5 Electrochemical active surface area (ECSA) The ECSA of the electrode was evaluated from their double layer electrochemical capacitances in a non-faradic region by a simple cyclic voltammetry method. The double layer current is equal to the product of the scan rate and the capacitance, which is expected to be linearly proportional to the active surface area of electrode. The current density differences were obtained at the median potential of the potential range. By plotting the capacitive currents (J anodic - J cathodic ) vs. scan rate, the ECSA can be estimated as half of the slope. Figure S6. Electrochemical capcacitance measurements of the ECSA of a) FeNiP@C and b) FeNiP in 1M KOH. Cyclic voltammograms in the region of 0.23 to 0.33 V vs RHE. Figure S7. a) and b) SEM images of FeNiP shelled with a carbon coating by hydrothermal carbonization of glucose for 6h (FeNiP@C-2). c) and d) ECSA evaluations for FeNiP@C-2. S-5

6 Figure S8. SEM image of post-oer electrode. Figure S9. a) XPS survey spectrum and b) high-resolution P 1s spectrum of FeNiP and FeNiP@C after the OER tests at the same current density for 2h. S-6

7 Figure S10. XRD cgaracterizations of the electrode before and after the electrochemical OER test in 1M KOH. Excepting the three main peaks of metallic nickel from Ni foam substrate, only the typical peaks of Ni 2 P can be observed. Figure S11. High resolution XPS spectra for P 2p of FeNiP@C before and after two-hour OER in 1M KOH. Movie S1. OER process at high current density on the FeNiP@C electrode in 1M KOH. The fast arise of oxygen bubble indicates the good gas desorption ability. Movie S2 Hydrogen generation cell in the electrolyte of 5 mm H 2 SO mg/l MB. The hydrogen was produced at FeNiP@C and no oxygen was generated on graphite (anode) due to the OER was substutited by MB decomposition. S-7

8 Table S1. Comparison of recently reported non-precious metal electrocatalysts for OER in alkline medium. (j: current density; η: overpotential; NF: Ni foam) Catalyst Mass loading (mg cm -2 ) j/ma cm -2 η/mv Tafel slope (mv/dec) Reference FeNiP@C This work Fe(PO 3 ) 2 /Ni 2 P/NF D Se- (NiCo)S x /(OH) x (Fe 0.5 Ni 0.5 ) 2 P/NF Fe-CoP/Carbon cloth NiFe-OH/NiFeP/NF FeNi-P nanoparticlestack array/nf 2.86 ± Ni 60 Fe 30 Mn Proc. Nat. Acad. Sci. 2017, Adv. Mater. 2018, Nano Energy 2017, 38, 553. Adv. Mater. 2017, 29, ACS Energy Lett. 2017, 2, J. Mater. Chem. A, 2017, 5, Energy Environ. Sci. 2016, 9, 540. G-FeCoW/Gold foam Science 2016, 352, 333. Ni x Fe 1-x Se 2 -DO/NF FeOOH/Co/FeOOH /NF Ni:Pi-Fe/NF Co/Co 2 P/NF MoS 2 /Ni 3 S 2 /NF Ni 0.51 Co 0.49 P/NF FeNi 3 N/NF Nat. Commun. 2016, 7, Angew. Chem. Int. Ed. 2016, 55, Chem. Mater. 2016, 28, ACS Energy Lett. 2016, 1, Angew. Chem. 2016, 128, Adv. Funct. Mater. 2016, 26, Chem. Mater. 2016, 28, S-8

9 Table S2 The concentrations of Fe, Ni, and P in the post-oer electrolytes that corresponding to FeNiP and FeNiP@C were determined by ICP-MS, respectively. The tests for the two electrodes corresponding eletrolytes were conducted three times, respectively. Electrolyte Time Fe (ppm) Ni (ppm) P (ppm) Time 1# < < FeNiP Time 2# < < Time 3# < < Average < < Time 1# < < FeNiP@C Time 2# < < Time 3# < < Average < < Note: Negative value indicates that no corresponding element was detected in the electrolytes. Figure S12. Nyquist plots of FeNiP and FeNiP@C electrode in 5mM H 2 SO 4 + 5mg/L MB. The voltage was applied at -0.1 V vs RHE. S-9

10 Figure S13. The liquid chromatogram of the MB solution (a) before and (b) after the decomposition. S-10