N-Doped Carbon Quantum Dots (N-CQDs) Modified WO3 Mesoporous Photoanode
for Efficient Solar Water Oxidation
Mabrook S. Amer, Mohmed A. Ghanem, and Abdullah M. Al-Mayouf
Results
Materials and Research Methodology
Introduction
Water splitting through photoelectrochemical (PEC) methods is a suitable technology for the generation of hydrogen fuel.
(b)
Characterization
of mes-WO3 and NCQDs/mes-WO3 composite
The ordered mesoporous WO3 photoanode was fabricated via dip-coating method by evaporation
Semiconductor metal oxides (SMOs) photoelectrodes such as Fe2O3, TiO2 , ZnO, and BiVO4, represents a very promising approach
)‫(النتائج‬
induced self-assembly (EISA) using THF as solvent and PEO-b-PS as templates.
(a)
(b)
(a)
180
Quantity Adsorbed (cm /g STP)
for transforming solar energy into fuels and received considerable attention in the last decade. Among of them, Tungsten trioxide
FTO
m-WO3
(b)
m-WO3 -450 A
CQDs/m-WO3
bullk-WO3
150
7-NCQDs/m-WO3
favorable valance band edge position for water oxidation (3 V vs NHE), and relative photochemical stability.
FTO substrate
Intensity (a.u.)
3
(WO3) is one of the best candidates for solar water splitting due to its visible-light response (band gap, Eg = 2.6 – 2.8 eV), a
m-WO3 -350N-450A
120
90
60
30
As-made inorganicorganic composite
100 nm
0
0.0
0.2
(d)
(c)
m-WO3
2.5
semiconductor photoanode.
Absorbance (a.u.)
Figure.1. (a) Solar water splitting systems in a semiconductor and (b) photo-electrochemical water splitting using n-type
0.21 nm
CQDs (100)
THF solvent
(c)
CQDs/m-WO3
Structure-directing agent
(PEO-b-PS)
5
Soft-templating Methods
1.5
Water soluble N-CQDs
2.0
(a)
350
400
450
500
550
600
650
2.0
2.5
3.0
3.5
NCQDs/m-WO3
Figure.4. (a) N2 sorption isotherms mesoporous WO3 and bulckWO3 samples, (b,c) XRD patterns and UV-Vis absorption of mWO3, CQDs/m-WO3 and N doped CQDs/m-WO3 composites,
Tauc plots of the m-WO3, and NCQDs/m-WO3 electrodes.
WO3-dark
(b)
1.2
2500
2000
1500
0.8
1000
Reticular chemistry
guiding approach
0.3
0.6
0.9
Potential applied (V vs SCE)
1.2
(c)
NCQDs/m-WO3
1.2
500
0
0
CQDs/m-WO3
1.4
NCQDs /m-WO3 dark
3000
1.6
m-WO3
WO3-light
NCQDs /m-WO3 light
0.0
1.0
light-off
0.8
0.6
0.4
0.2
light-on
0.0
500
1000
1500
2000
Z' ( )
2500
3000
0
2000
4000
6000
N-CQDs/mes-WO3
Time (s)
Discussion and Recommendations
Tungsten trioxide (WO3) is one of the best candidates for solar water splitting due to its visible-light response (band gap, Eg = 2.6 –
This work includes the fabrication and characterization of a novel tungsten trioxide WO3 mesoporous photoelectrode via surfactant self-
Results
2.8 eV), a favorable valance band edge position for water oxidation (3.0 V vs NHE), and relative photo-corrosion stability. However,
WO3 suffer from some limitations, it’s not stable in neutral and alkaline electrolytes due its degradation in these conditions and
)‫(النتائج‬
Characterization of CQDs and NCQDs
hence is commonly evaluated in low pH conditions. Moreover, WO3 is very low onset potentials towards the OER around 0.2 V vs
530 Ex
340 nm
360
400
420
440
460
480
500
520
540
(a)
Intensity ( a.u.)
beneficial for the development of PEC cell architectures photoanodes.
Ex
(b)
NCQDs-7%
(c)
Em
assembly and a dip-coating method using a high molecular-weight PEO-b-PS copolymer as a structure-directing template followed by the
incorporation of N-CQDs within the ordered mesostructure through impregnation assembly.
Importantly, the resulting N-CQD/meso-WO3 nanocomposites demonstrated significantly enhanced PEC performance, with high
photocurrent densities (1.45 mA cm−2 at 1.23 V vs. RHE) and low onset potentials (negatively shifted by 94 mV) compared to those of
pristine meso-WO3.
Furthermore, the N-CQD/meso-WO3 photoanode demonstrated a high applied bias photon-to-current conversion efficiency (ABFE) of
0.16% at 1.0V vs. RHE.
Conclusion
• Synthesis of mesoporous N-CQD/meso-WO3 photoanodes by evaporation induced self-assembly (EISA) template and
In summary, the N doped CQDs composed of rich functional groups are incorporated onto mesoporous WO3 photoanode via
chemical imbergnation method.
impregnation method. Owing to N doping, the conductivity and charge separation and transfer process can be improved, which
area, TEM and SEM techniquse.
• Evolution of PEC oxygen production efficiency and stability of the produced N-CQD/meso-WO3 mesoporous photoanodes
by potoelectrochemical experimental using solar water splitting techniques.
References
[1] Li, Wei; Liu, Jun; Zhao, Dongyuan, Mesoporous materials for energy conversion and storage devices.
Nature Reviews Materials, May 2016.
[2] B. S. Kalanoor, H. Seo, S. S. Kalanur, Recent developments in photo-electrochemical water-splitting
using WO3/BiVO4 heterojunction photoanode: A review. Material Science for Energy Technologies, (2018)
49-62
[3] Debraj Chandra, Kenji Saito, Tatsuto Yui, and Masayuki Yagi, "Tunable Mesoporous Structure of
Crystalline WO3 Photoanode toward Efficient Visible-Light-Driven Water Oxidation." ACS Sustainable
Chemistry & Engineering 6.12 (2018): 16838-16846.
8000
Figure.5. (a) Chopped cyclic voltammograms for mes-WO3 , CQDs/ mes-WO3 NCQDs/mes-WO3, (b) EIS Nyquist plots (d) Current-time
response curve of the of pure m-WO3 and NCQDs/m-WO3 in the dark and under the illumination of AM 1.5G illumination.
FTO substrate
• Physicochemical characterizations of the obtained N-CQD/meso-WO3 mesoporous photoanodes using XRD, BET surface
4.0
hv (eV)
1.6
3500
0.0
Research Problem
0
2
CQDs/m-WO3
-Z'' ()
Current Density ( mAcm-2)
m-WO3
0.4
N-CQD/meso-WO3 photoanode for water splitting. The specific objectives are to:
2
1
4000
2.4
dried at 80 ºC
The main objective of this work is to elucidate the boosting effect of N-CQDs on the photoelectrochemical performance of
3
Photoelectrochemical Properties of photoanodes
Rinsed with DI-water
Research goals
80
2.63eV
Figure.3. (a) FESEM images of mes-WO3 photoanode, (b) TEM
image of mes-WO3, (c,d) TEM
and
HRTEM images of
NCQDs/meso-WO3 photoanode.
Hydrothermal treatment
Melamine
AgCl at pH=7. Therefore, the possibility to fabricate WO3 photoanode able to operate to at near-neutral pH aqueous solutions is
70
(d)
Wavelenthge (nm)
180 ºC for 5 h
Template-free packing method
0.5
300
Immersed in NCQDs solution
In-situ templating pathway
60
4
2.0
0.0
FTO substrate
Crystalline mesoporous WO3
Methods to synthesize mesoporous materials
Multiple-templating method
50
2.71 eV
lifetime and stability.
Hard-templating Methods
40
NCQDs-7/m-WO3
WO3 (020)
Metal Precursor
Sucrose
30
m-WO3
NCQDs/m-WO3
Current Density (mA/cm )
areas and large pore volumes. These properties may improve the performance of materials in terms of energy and power density,
0.382 nm
20
2 Theta (degree)
1.0
Mesoporous materials offer opportunities in energy conversion and storage applications due to their extraordinarily high surface
10
1.0
(ahv)^1/2
Amorphous metal oxidecarbon composite
0.4
0.6
0.8
Relative Pressure (P/P0)
300
350
400
450
500
550
600
650
700
Wavelength (nm)
Figurer.2., (a) UV-Vis absorption spectra for the CQDs and NCQDs samples. Inserts show digital photos of aqueous NCQDs-7
(left) and their bright blue PL (right) under UV. (b) PL spectra for the NCQDs-7, the excitation wavelength was increased from 340
to 540 nm in 20 nm increments. (d) TEM image of NCQDs-7 sample.
induces the significant PEC enhancement.
The photocurrent density of the N-CQD/meso-WO3 photoanode exhibits 2.25-fold
enhancement (1.45 mA cm−2 at 1.23 V vs RHE) accompanied with a negative shift of 90 mV in onset potential in contrast to the bare
WO3 mesoporous.
These results highlighted the multifunctional role of hybridization of mesoporous WO3 with N-doped CQDs in the enhancement of
PEC solar water splitting.