Supporting Information Oxygen Intercalated CuFeO2 Photocathode ...
Supporting Information Oxygen Intercalated CuFeO2 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 790-784, Korea ‡ School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea § Division of Advanced Nuclear Engineering, Pohang University of Science and Technology(POSTECH), Pohang 790-784, South Korea ∥ Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea
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 oC (CFO 500 Ar), 600 oC (CFO 600 Ar), and 700 oC (CFO 700 Ar) for 10 h. * represents peaks of SnO2 from FTO substrate. The insets are photographs of films to show their transparency. B: Powder XRD of copper iron oxide calcined at 450 oC in air and delafossite CuFeO2 annealed 700 oC in Ar with references CuFeO2 (JCPDS no.01-075-2146, red), Fe2O3 (JCPDS no. 01085-0599, blue), and Cu2O (JCPDS no. 01-078-2076, 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
Figure S2. Cu K-edge (A) and Fe K-edge (B) XANES spectra of CuFeO2 electrodes annealed at different temperatures under Ar flow.
Figure S3. k3-weighted Fourier transforms of Fe K-edge EXAFS functions for annealed CuFeO2 photocathodes: (A) FT magnitude, (B) imaginary function.
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 oC, (C) annealed in Ar flow at 600 oC and (D) annealed in Ar flow at 700 oC for 10 h.
Figure S5. Current(J) – potential(V) curves of the photocathodes measured under the chopped illumination of the simulated 1 sun in Ar-purged electrolyte.
Figure S6. A: X-ray diffraction (XRD) patterns, B: Depth profiled ratios of Cu2+/(Cu2+ + 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..
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 CuFe2O4 as highlighted with red.
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).
Figure S9. A: Linear sweep voltammetry of Pt, NiFe LDH, NiFe LDH/RGO on a Ni foam in 1 M NaOH electrolyte.
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 CuFeO2 films deposited with NiFe (HMA-NiFe; A2) and NiFe/RGO (HMA-NiFe/RGO; B2)
Figure S11. IPCE results for CFO, CTA, HMA and HMA-NiFe/RGO. The inset is the integrated photocurrent based on IPCE.
Figure S12. A: XRD, XPS of Cu (B), Fe (C) and Ni (D) for before/after HMA-NiFe/RGO.
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 H2 and O2, and the H2/O2 stoichiometry over CFO, XPS of Cu (C) and Fe (D) for before/after tested CFO.
Table S1. Summary of performances of reported copper based photocathodes for solar hydrogen generation Electrode
Photocurrent [mAcm-2]
Potential [V vs. RHE]
CuFeO2
-0.3
0.4
CuFeO2-HMA
- 1.3
0.4
CuFeO2HMA/NiFe LDHRGO
-2.4
0.4
Cu2O/AZO/TiO2/Pt
ca. -1.0
0.3
1 M Na2SO4N2
8
CuGaSe2/CdS/Pt
ca. -3.3
0.4
0.1 M Na2SO4
12
-25 μAcm
0.4
1 M NaOH
ca. -1.51
0.35
1 M NaOH-O2
CuFeO2
-0.98
0.4
1 M NaOH-O2
CuFeO2/ CuAlO2
-1.95
0.4
1 M NaOH-O2
ca. -0.3
0.4
1 M NaOH-N2
ca. -0.9
0.4
1 M NaOH-O2
CuO-HMA
ca. -0.75
0.3
0.5 M Na2SO4
31
CuFeO2/CuO
ca. -0.8
0.4
1 M KHCO3N2
42
-2
CuFeO2
CuFeO2
Electrolyte
Light Source
Reference This work This work
1 M NaOH – Ar
This work
1 sun 18
19
20
† Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea ‡ School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea § Division of Advanced Nuclear Engineering, Pohang University of Science and Technology(POSTECH), Pohang 790-784, South Korea ∥ Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea
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 oC (CFO 500 Ar), 600 oC (CFO 600 Ar), and 700 oC (CFO 700 Ar) for 10 h. * represents peaks of SnO2 from FTO substrate. The insets are photographs of films to show their transparency. B: Powder XRD of copper iron oxide calcined at 450 oC in air and delafossite CuFeO2 annealed 700 oC in Ar with references CuFeO2 (JCPDS no.01-075-2146, red), Fe2O3 (JCPDS no. 01085-0599, blue), and Cu2O (JCPDS no. 01-078-2076, 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
Figure S2. Cu K-edge (A) and Fe K-edge (B) XANES spectra of CuFeO2 electrodes annealed at different temperatures under Ar flow.
Figure S3. k3-weighted Fourier transforms of Fe K-edge EXAFS functions for annealed CuFeO2 photocathodes: (A) FT magnitude, (B) imaginary function.
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 oC, (C) annealed in Ar flow at 600 oC and (D) annealed in Ar flow at 700 oC for 10 h.
Figure S5. Current(J) – potential(V) curves of the photocathodes measured under the chopped illumination of the simulated 1 sun in Ar-purged electrolyte.
Figure S6. A: X-ray diffraction (XRD) patterns, B: Depth profiled ratios of Cu2+/(Cu2+ + 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..
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 CuFe2O4 as highlighted with red.
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).
Figure S9. A: Linear sweep voltammetry of Pt, NiFe LDH, NiFe LDH/RGO on a Ni foam in 1 M NaOH electrolyte.
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 CuFeO2 films deposited with NiFe (HMA-NiFe; A2) and NiFe/RGO (HMA-NiFe/RGO; B2)
Figure S11. IPCE results for CFO, CTA, HMA and HMA-NiFe/RGO. The inset is the integrated photocurrent based on IPCE.
Figure S12. A: XRD, XPS of Cu (B), Fe (C) and Ni (D) for before/after HMA-NiFe/RGO.
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 H2 and O2, and the H2/O2 stoichiometry over CFO, XPS of Cu (C) and Fe (D) for before/after tested CFO.
Table S1. Summary of performances of reported copper based photocathodes for solar hydrogen generation Electrode
Photocurrent [mAcm-2]
Potential [V vs. RHE]
CuFeO2
-0.3
0.4
CuFeO2-HMA
- 1.3
0.4
CuFeO2HMA/NiFe LDHRGO
-2.4
0.4
Cu2O/AZO/TiO2/Pt
ca. -1.0
0.3
1 M Na2SO4N2
8
CuGaSe2/CdS/Pt
ca. -3.3
0.4
0.1 M Na2SO4
12
-25 μAcm
0.4
1 M NaOH
ca. -1.51
0.35
1 M NaOH-O2
CuFeO2
-0.98
0.4
1 M NaOH-O2
CuFeO2/ CuAlO2
-1.95
0.4
1 M NaOH-O2
ca. -0.3
0.4
1 M NaOH-N2
ca. -0.9
0.4
1 M NaOH-O2
CuO-HMA
ca. -0.75
0.3
0.5 M Na2SO4
31
CuFeO2/CuO
ca. -0.8
0.4
1 M KHCO3N2
42
-2
CuFeO2
CuFeO2
Electrolyte
Light Source
Reference This work This work
1 M NaOH – Ar
This work
1 sun 18
19
20
