Supporting Information. Oxygen Intercalated CuFeO 2 Photocathode Fabricated by Hybrid Microwave Annealing for Efficient Solar Hydrogen Production

Transcription

1 Supporting Information Oxygen Intercalated CuFeO 2 Photocathode Fabricated by Hybrid Microwave Annealing for Efficient Solar Hydrogen Production Youn Jeong Jang, Yoon Bin Park, Hyo Eun Kim, Yo Han Choi, Sun Hee Choi, Jae Sung Lee * Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang , Korea School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan , Korea Division of Advanced Nuclear Engineering, Pohang University of Science and Technology(POSTECH), Pohang , South Korea Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang , Korea

2 Figure S1. A: X-ray diffraction (XRD) patterns of copper iron oxide annealed at different conditions; as spin-coated (CFO 450 Air), and as annealed under Ar flow at 500 o C (CFO 500 Ar), 600 o C (CFO 600 Ar), and 700 o C (CFO 700 Ar) for 10 h. * represents peaks of SnO 2 from FTO substrate. The insets are photographs of films to show their transparency. B: Powder XRD of copper iron oxide calcined at 450 o C in air and delafossite CuFeO 2 annealed 700 o C in Ar with references CuFeO 2 (JCPDS no , red), Fe 2 O 3 (JCPDS no , blue), and Cu 2 O (JCPDS no , green). The powder samples were prepared using the same precursor solution of film fabrication. C: X-ray photoelectron spectra of Sn 3d for CFO 600 Ar and CFO 700 Ar samples

3 Figure S2. Cu K-edge (A) and Fe K-edge (B) XANES spectra of CuFeO 2 electrodes annealed at different temperatures under Ar flow.

4 Figure S3. k 3 -weighted Fourier transforms of Fe K-edge EXAFS functions for annealed CuFeO 2 photocathodes: (A) FT magnitude, (B) imaginary function.

5 Figure S4 High resolution scanning electron microscopy (SEM) images showing surface morphologies of the films: (A) Copper iron oxide thin film as spin-coated and annealed at 450 in air, (B) annealed in Ar flow at 500 o C, (C) annealed in Ar flow at 600 o C and (D) annealed in Ar flow at 700 o C for 10 h.

6 Figure S5. Current(J) potential(v) curves of the photocathodes measured under the chopped illumination of the simulated 1 sun in Ar-purged electrolyte.

7 Figure S6. A: X-ray diffraction (XRD) patterns, B: Depth profiled ratios of Cu 2+ /(Cu 2+ + Cu + ) from X-ray photoelectron spectra (XPS) of Cu 2p, C: Scheme of heating mechanism using hybrid microwave annealing, 37 D,E,F: XPS of Cu 2p for bare CFO 600 and HMA and CTA treated CFO, respectively..

8 Figure S7. XRD patterns of copper iron oxide post-treated by HMA with a graphite susceptor. The inset is a blow-up of the XRD pattern showing characteristic peaks of spinel CuFe 2 O 4 as highlighted with red.

9 Figure S8. UV-Vis Diffuse Reflectance Spectra (UV-Vis DRS) (A) and the calculated absorbed photon flux relative to illuminated 1 sun (B) of unannealed CFO, post-hybrid microwave annealing (HMA) and post-conventional thermal annealing (CTA).

10 Figure S9. A: Linear sweep voltammetry of Pt, NiFe LDH, NiFe LDH/RGO on a Ni foam in 1 M NaOH electrolyte.

11 Figure S10. SEM images showing morphologies of NiFe layered double hydroxide (NiFe; A1) and NiFe/reduced graphene oxide composite (NiFe/RGO; B1). Bottom SEM images show surface morphologies of HMA-treated CuFeO 2 films deposited with NiFe (HMA-NiFe; A2) and NiFe/RGO (HMA-NiFe/RGO; B2)

12 Figure S11. IPCE results for CFO, CTA, HMA and HMA-NiFe/RGO. The inset is the integrated photocurrent based on IPCE.

13 Figure S12. A: XRD, XPS of Cu (B), Fe (C) and Ni (D) for before/after HMA-NiFe/RGO.

14 Figure S13. A: Hydrogen (blue) and oxygen (red) evolutions from water splitting over bare CFO photocathode during chronoamperemetry test (black) under 1 sun illumination in Arpurged electrolyte for 1 h. B: Calculated faradaic efficiencies for H 2 and O 2, and the H 2 /O 2 stoichiometry over CFO, XPS of Cu (C) and Fe (D) for before/after tested CFO.

15 Table S1. Summary of performances of reported copper based photocathodes for solar hydrogen generation Electrode Photocurrent [macm -2 ] Potential [V vs. RHE] Electrolyte Light Source Reference CuFeO CuFeO 2 -HMA CuFeO 2 - HMA/NiFe LDH- RGO Cu 2 O/AZO/TiO 2 /Pt ca M NaOH Ar 1 M Na 2 SO 4 - N 2 This work This work This work 8 CuGaSe 2 /CdS/Pt ca M Na 2 SO 4 12 CuFeO 2-25 μacm M NaOH 1 sun 18 ca M NaOH-O 2 CuFeO M NaOH-O 2 CuFeO 2 / CuAlO M NaOH-O 2 19 CuFeO 2 ca M NaOH-N 2 ca M NaOH-O 2 20 CuO-HMA ca M Na 2 SO 4 31 CuFeO 2 /CuO ca M KHCO 3 - N 2 42