Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide

Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type
low bandgap double perovskite oxide
PAWAN KUMAR1, Suresh Mulmi2, Devika Laishram3, Kazi Mohammad Alam4, Ujwal Kumar Thakur4, V
Thangadurai5 and Karthik Shankar4
This work has been published in IOP Nanotechnology
Please cite DOI: https://doi.org/10.1088/1361-6528/abedec
Please visit: https://choudhary2486pawan.wixsite.com/pawankumar

Fig. 1. Synthesis protocol for formation of Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ/g-C3N4 (BCNFCo/CN)
nanocomposite.

Fig. 2. TEM images of CN (a) Low magnification image at 0.5 µm scale bar and (b) Moderate magnification image at 100 nm scale bar showing nanosheets
structure (c) HR-TEM image at 10 nm scale bar showing nanoporous structure; inset showing corresponding FFT image (d) HR-TEM of BCNFCo/CN
nanohybrid at 5 nm scale bar 50 nm scale bar showing wrapped CN over BCNFCo. (e) HR-TEM images of BCNFCo/CN at 5 nm scale bar demonstrating
BCNFCo entrapped in CN matrix, Inset 1 and 2 are FFT of selected region showing amorphous CN and crystalline BCNFCo domains (f) Enlarged region
showing close contact between CN and BCNFCo and iFFT showing lattice fringes overlapping with crystal plane of BCNFCo and corresponding d-spacing (g)
High magnification image at 5 nm scale bar showing lattice fringes of double perovskite oxide and wrapping of CN around the lattice; inset FFT of entire
images and (f) Magnified view of the selected area showing interplanar d-spacing and corresponding iFFT overlapped showing 0.27 nm d-spacing.

Fig. 3. STEM EDX elemental mapping of 40% BCNFCo/CN nanocomposite (a) Bright field (BF) image of mapped area,
and EDX elemental mapping for (b) Ba (red), (c) Ca (blue), (d) Co (green), (e) Fe (cyan), (f) Nb (magenta), (g) O (pink), (h)
C (yellow), (i) N (violet); (j) Composite image for Ba, Ca, Co, Fe, Nb, O (k) composite of C, N and (l) Composite of Ba,
Ca, Co, Fe, Nb, O, C and N.

Fig. 4. (a) FTIR spectra of BCNFCo, CN and 40% BCNFCo/CN, (b) Raman spectra of BCNFCo, CN and 40%
BCNFCo/CN (c) Powder XRD (P-XRD) diffraction pattern of CN, BCNFCo and their composites with different wt%;
Color: CN (black), 10% BCNFCo/CN (pink), 20% BCNFCo/CN (green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN
(red), 50% BCNFCo/CN (yellow), BCNFCo (violet).

Fig. 5. (a) DR-UV-Vis spectra and (b) Steady-state PL (ssPL) spectra of CN, 10% BCNFCo/CN, 20% BCNFCo/CN, 30%
BCNFCo/CN, 40% BCNFCo/CN, 50% BCNFCo/CN, BCNFCo acquired at 360 nm excitation; Color: CN (black), 10%
BCNFCo/CN (pink), 20% BCNFCo/CN (green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN
(yellow), BCNFCo (violet).

Fig. 6. (a) Linear sweep voltammograms of CN, 10% BCNFCo/CN, 20% BCNFCo/CN, 30% BCNFCo/CN, 40% BCNFCo/CN, 50% BCNFCo/CN,
BCNFCo samples showing change in photocurrent density vs applied potential (J-V), under dark and simulated solar AM1.5G light irradiation (100 mW
cm−2) (b) Photocurrent vs time (i-t) plot showing response during light On-Off cycles at +0.6 V applied bias, under AM1.5G light irradiation (100 mW
cm−2); All the measurements were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec and (c) Calculated Faradaic efficiencies for hydrogen
evolution using BCNFCo, CN and 40% BCNFCo/CN photocatalyst.

Fig. 7. (a) Linear sweep voltammogram of 40% BCNFCo/CN showing photocurrent density vs applied potential (J-V), photoresponse during light On-Off
cycle under dark, solar simulated AM1.5G light irradiation without filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (b)
Photocurrent vs time (i-t) plot of 40% BCNFCo/CN showing response during light On-Off cycle at +0.6 V applied bias, under solar simulated AM1.5G light
irradiation without filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of 40% BCNFCo/CN
during the light On-Off cycle at +0.6 V applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph
showing photoresponse of 40% BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution
at a scan rate of 0.1 mV/sec.

Fig. 8. XPS valence band (XPS-VB) spectra showing valence band position with respect to Fermi level of (a) CN, (b)
BCNFCo and (c) 40% BCNFCo/CN and Mott-Schottky plots showing flat and potential of CN (black), 10% BCNFCo/CN
(pink), 20% BCNFCo/CN (green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow).

Fig. 9. A plausible mechanism of Fermi level alignment and formation of p-n heterojunction between BCNFCo and CN.

Figure S1. Inner shell ionization edge (core loss) electron energy loss spectra (EELS) of graphitic carbon nitride
(CN) showing contribution of σ* and π* signals in C K-edge and N K-edge energy loss.

Figure S2. STEM EDX elemental mapping of 40% BCNFCo/CN nanocomposite (a) bright field (BF) image of mapped area
and EDX elemental mapping for (b) Ba (red), (c) Ca (blue), (d) Co (green), (e) Fe (cyan), (f) Nb (magenta), (g) O (pink), (h) C
(yellow), (i) N (violet), (j) composite image for Ba, Ca, Co, Fe, Nb, O (k) composite of C, N, (l) composite of Fe, Co and Nb
(m) composite of Co, Fe, C and N (n) composite of Ba, Nb and N (o) composite of Ba, Ca, Co, Fe, Nb, O, C and N.

Figure S3. (a) RGB composite of EDX elemental mapping for Ba (red), C (green), N (blue) (b) Line scan of RGB composite
showing the relative distribution of each elements, (c) RGB composite of EDX elemental mapping for Ca (red), C (green), N
(blue) (b) Line scan of RGB composite showing the relative distribution of each elements

Figure S4. (a) XPS elemental
survey scan of CN, and HR-XPS
spectra of CN in (b) C1s, (c) N1s,
and (d) O1s regions.

Figure S5. (a) XPS elemental survey scan of
BCNFCo, and HR-XPS spectra of BCNFCo in (b)
Ba3d, (c) Ca2p, (d) Nb3d, (e) Fe2p, (f) O1s region

Figure S6. (a) XPS elemental survey
scan of 40% BCNFCo/CN composite,
and HR-XPS spectra of 40%
BCNFCo/CN in (b) C1s, (c) N1s, (d)
Ba3d, (e) Ca2p, (f) Nb3d, (g) Fe2p, (h)
O1s region.

Figure S7. (a) Tauc plot of CN (black), 10% BCNFCo/CN (pink), 20% BCNFCo/CN (green), 30% BCNFCo/CN
(blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow), BCNFCo (violet).

Figure S8. An idealized crystal structure of cubic double-perovskite Ba3CaNb2O9.

Figure S9. Powder X-ray diffraction (PXRD) Rietveld refinement plot of double-perovskite-
type Ba2Ca0.67Nb0.67Fe0.33Co0.33O6-δ using Fm-3m (No. 225) space group.

Figure S10. TGA thermogram of CN
(blue) and 40% BCNFCo/CN catalyst

Figure S11. GC chromatogram of
the cathodic gaseous product on Pt
counter electrode, showing peaks for
evolved H2 in PEC water splitting
using BCNFCo, CN and 40%
BCNFCo/CN photocatalyst under
AM1.5 irradiation (100 mW cm-2).

Figure S12. Experimental (points) and fitted (line) EIS Nyquist plots of (a) CN (black), 10% BCNFCo/CN (pink), 20% BCNFCo/CN
(green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow), BCNFCo (violet) under dark and (b) CN (black),
10% BCNFCo/CN (red), 20% BCNFCo/CN (magenta), 30% BCNFCo/CN (navy blue), 40% BCNFCo/CN (violet), 50% BCNFCo/CN
(yellow), BCNFCo (blue) under AM1.5 G solar simulated light (100 mW cm-2). Insets shows Equivalent circuit of EIS data under dark and
illumination conditions respectively.

Figure S13. (a) Linear sweep voltammogram of CN showing photocurrent density vs applied potential (J-V), photoresponse during light On-Off cycle under
dark, solar simulated AM1.5G light irradiation without filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (b) Photocurrent vs time (i-t)
plot of CN showing response during the light On-Off cycle at +0.6 V applied bias, under solar simulated AM1.5G light irradiation without filter (100 mW cm−2)
and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of CN during the light On-Off cycle at +0.6 V applied bias, under 420,
460, 520, 580, 640, 740 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of CN under 580, 640, 740 and 840 nm
LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

Figure S14. (a) Linear sweep voltammogram of BCNFCo showing photocurrent density vs applied potential (J-V), photoresponse during light On-Off cycle under
dark, solar simulated AM1.5G light irradiation without filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (b) Photocurrent vs time (i-t)
plot of BCNFCo showing response during the light On-Off cycle at +0.6 V applied bias, under solar simulated AM1.5G light irradiation without filter (100 mW
cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of BCNFCo during the light On-Off cycle at +0.6 V applied bias,
under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of BCNFCo under 580, 640 and 840
nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

Figure S15. (a) Linear sweep voltammogram of 10% BCNFCo/CN showing photocurrent density vs applied potential (J-V), photoresponse during light On-Off
cycle under dark, solar simulated AM1.5G light irradiation without filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (b) Photocurrent
vs time (i-t) plot of 10% BCNFCo/CN showing response during light On-Off cycle at +0.6 V applied bias, under solar simulated AM1.5G light irradiation without
filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of 10% BCNFCo/CN during the light On-Off
cycle at +0.6 V applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of
10% BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of 20% BCNFCo/CN during the light On-Off
cycle at +0.6 V applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of
20% BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of 30% BCNFCo/CN during the light On-Off cycle
at +0.6 V applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of 30%
BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

filter (100 mW cm−2) and AM1.5G light irradiation with 420 nm cut-off filter, (c) Photocurrent response vs time of 50% BCNFCo/CN during the light On-Off cycle
at +0.6 V applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2) (d) Enlarged photocurrent vs time graph showing photoresponse of 50%
BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2) All the measurement were performed in 0.1 M Na2SO4 solution at a scan rate of 0.1 mV/sec.

Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide

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