http://support.spring8.or.jp/Report_JSR/PDF_JSR_2021A/2021A1640.pdf

2021A1640

BL14B2

CEY-XANES Studies on CuxO/rGO/Cu Photoelectrocatalyst
Rozan Mohamad Yunus a, Takeshi Watanabe b, Junji Iukai a,ca

Universiti Kebangsaan Malaysia (UKM), b JASRI, c University of Yamanashi

Abstract
For the reduction of CO2, we have synthesized thin films of CuO on a Cu substrate (CuxO/rGO/Cu).
To understand the chemical composition of CuxO in CuxO/rGO/Cu, CEY-XANES measurements werecarried out at room temperature in air at the beamline BL14B2 of SPring-8. It was found that 10–20%
was Cu metal and the rest was Cu oxides. Further studies are needed to understand the composition ofthe Cu oxides.
Keywords: Photocatalysts, CuxO/rGO/Cu, CEY-XANES, oxidation states
Background and Purpose of Research:
Reduction of CO2 by photocatalytic methods is gaining extensive attentions, change CO2 intohydrocarbon fuels such as alcohols, carbon monoxide, and other gas and liquid products using solar
energy. Cuprous oxide (Cu2O), with a direct band gap (2.0 eV) has green characteristics: non-toxic andcompatible with environment. The promising band gap and relevant arrangement of the conduction andvalence bands, make it an excellent photocatalyst for CO2 photoreduction. A chemical compound of sp2
hybridized carbon atoms, graphene, a two-dimensional monolayer, has drawn attentions in recent years
because of its attractive physical and chemical properties. In general, graphene is a zero band gap
semiconductor with asymmetric band structure.
Only few researches have been carried out in relation to the integration of CuO with carbonaceous
materials. We have synthesized thin films of CuO on a Cu substrate [1, 2]. A p-type reduced graphene(rGO) layer was introduced to cover the CuO layer through a simple hydrothermal method. Throughphotoelectrochemical measurements, the superior properties of our CuxO/rGO/Cu photocatalyst:
significant high photocurrent up to 9.6 mA cm−3 at 0.8 V vs. Ag/AgCl. From the preparation in one-pot
hydrothermal approach, the film can directly use as photoelectrodes in photoelectrochemical cell.
Therefore, the study to understand the nature of CuO/rGO/Cu will gives insight on implications on theoverall photoconversion efficiency.
From the XRD spectra, when the hydrothermal reaction time is increased from 1 hour to 3 hours, theintensity of the CuO peaks is negligible. Due to the low amount and amorphous nature of CuO, the peak
was not recognized in the XRD analysis. We extended the analysis using XPS to examine the existenceof CuO element, and the presence of CuO was affirm from the two main peaks at 932.52 and 952.53 eVcorresponding to Cu 2p3/2 and Cu 2p1/2, respectively. Although, this technique provides information
regarding the oxidation state of copper in the certain thin samples, the bulk composition could not beobtained. Therefore, CEY-XANES measurements were carried out to understand the bulk composition.
Experimental:
Four samples were prepared in Fuel Cell Institute in UKM, Malaysia as listed below:
Sample A: Cu foil in DMF solvent (3-hour reaction time)
Sample B: Cu foil in DMF with hydrazine as reduction agent (3-hour reaction time)
Sample C: Cu foil with Graphene Oxide (GO) in DMF with hydrazine (3-hour reaction time)
Sample D: Cu foil with GO in DMF with hydrazine (24-hour reaction time)
The sample size was 2 cm × 2 cm with the thickness of 0.25 mm. The thickness of the CuxO/rGO
layer was estimated as 6 μm
On those samples, CEY-XANES of Cu (K-edge, 9.0 keV) in CuxO/rGO/Cu photoelectrocatalyst wascarried out at the beamline BL14B2 of SPring-8 in air at room temperature.

Results
Figure 1 shows the XANES spectra of Samples A to D and references of Cu2O, CuO, and Cu. The
white lines of Samples A to D were very different. The linear combination of the data from Sample A toD using those of Cu2O, CuO, and Cu had some ambiguities, probably because of the existence of trace
amounts of other components, such as CuOH and Cu(OH)2. As a first approximation, the fitting wasdone with the spectra of Cu and CuO as a representative of Cu oxides. The ratios were obtained as:
Sample A
Sample B
Sample C
Sample DCu metal : Cu oxides = 10 : 0Cu metal : Cu oxides = 2 : 8Cu metal : Cu oxides = 2 : 8Cu metal : Cu oxides = 1 : 9

The details of the composition of the Cu oxides are still unknown. A combination of Rietveld
refinement on X-ray diffraction
patterns and EXAFS is expected to understand the chemical compositions, as well as structures.

Fig. 1 XANES spectra of Samples A to D and reference samples of Cu2O, CuO, and Cu.

References[1] R. M. Shah, R. M. Yunus, M. S. Masdar Mastar, L. J. Minggu, W. Y. Wong and A. A. H. Kadhum,Sains Malaysiana, 48 (6), 1233 (2019).
[2] R. M. Shah, R. M. Yunus, M. S. Masdar Mastar, L. J. Minggu, W. Y. Wong and A. A. H. Kadhum,International Journal of Energy Research, submitted.