Enhancing Photocurrent in Unannealed NiS x /CdS Photoelectrochemical System for Water Splitting and Hydrogen Production
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ENHANCING PHOTOCURRENT IN UNANNEALED NiSx/CdS PHOTOELECTROCHEMICAL SYSTEM FOR WATER SPLITTING AND HYDROGEN PRODUCTION Ning Zhang, Liejin Guo* Email: [email protected]; [email protected] State Key Laboratory of Multiphase Flow in Power Engineering (MPFL), School of Energy and Power Engineering, Xi’an Jiaotong University, Shaanxi, PR China ABSTRACT In this work, NiSx was deposited on FTO by chemical bath and worked as the inner layer in order to enhance the photocurrent of CdS film. It is found the unannealed CdS/NiSx had a higher photocurrent than unannealed CdS, but after annealing, the photocurrent of CdS/NiSx showed dramatical decrease. The mechanism was discussed in detail by UPS and current-potential curves. INTRODUCTION Recently, as fossil fuel supply will fall short of demand and global warming will become acute, the direct use of solar energy such as clean and renewable energy through visible-light-driven photoelectrochemistry using solar for water splitting and hydrogen production has attracted great interest. Many photocatalysts have been investigated, such as TiO2, CdS, and GaN. And a lot of efforts have been made to enhance the photocatalytic efficiency, such as coupling one photocatalyst with other semiconductors，loading noble metal as co-catalyst, and using sacrificial agent.[2] However the conversion efficiency and cost are still two key problems which limit the industrial application of photoelectrochemistry. Thus development of novel PEC system with ultra high efficiency is highly desired. CdS was proved to be an ideal photocatalyst, as it has a suitable band gap to absorb visible- light and relative high bottom of conduction band to reduce H+ into H2. But the photogenerated charges often recombine on the surface and/or in the bulk phase of CdS, which result in a very low photocurrent. It has been reported that NiSx worked as a co-catalyst in CdS system could significantly inhibit the recombination of photo generated charges.[1] In this paper, we propose an efficient method to enhance the photocurrent of CdS film by depositing a NiSx inner layer on FTO. The mechanism of this enhancing effect was discussed in detail.
EXPERIMENT
FTO glass (NSG, 15Ω/sq., 3cm
2cm) was used as substrate. The NiSx layer was deposited in
0.5M Ni(NO3)2, 0.5M thiacetamide, and 25% volume ratio triethanolamine mixed aqueous solution at 20 ℃ for 12 hours. The CdS layer was prepared by chemical bath deposition in an aqueous solution containing 0.01M Cd(Ac)2 ,0.01M Thiourea and 0.01M NH4Cl at 80 ℃ for 4h. Then the composite film was annealed at 500℃ in vacuum. The X-ray diffraction (XRD) patterns of as-prepared films were carried out on Panalytic X’pert Pro X-ray diffractometer equipped with Cu Kα irradiation. The diffuse reflectance UV-Vis spectra of the films were measured on a HITACHI UV4100 instrument employing a labsphere diffuse reflectance accessory. A convenient three electrodes cell was used to carry out electrochemical measurement. The prepared thin film was used as work electrode, and measured area was 0.785
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