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Effects of Al2O3 Coating on BiVO4 and Mo-doped BiVO4 Film for Solar Water Oxidation

  • Arunachalam, Maheswari (Department of Chemistry, Chonnam National University) ;
  • Yun, Gun (Department of Chemistry Education and Optoelectronic Convergence Research Center, Chonnam National University) ;
  • Lee, Hyo Seok (School of Materials Science and Engineering, Chonnam National University) ;
  • Ahn, Kwang-Soon (School of Chemical Engineering, Yeungnam University) ;
  • Heo, Jaeyeong (School of Materials Science and Engineering, Chonnam National University) ;
  • Kang, Soon Hyung (Department of Chemistry Education and Optoelectronic Convergence Research Center, Chonnam National University)
  • Received : 2019.06.25
  • Accepted : 2019.07.28
  • Published : 2019.12.31

Abstract

Planar BiVO4 and 3 wt% Mo-doped BiVO4 (abbreviated as Mo:BiVO4) film were prepared by the facile spin-coating method on fluorine doped SnO2(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO4 film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al2O3 layer, the ultra-thin Al2O3 layer with a thickness of approximately 2 nm was deposited on BiVO4 film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO4 and Mo:BiVO4 films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al2O3 layer, the Al2O3 coated BiVO4 (Al2O3/BiVO4) film exhibited enhanced photoelectrochemical performance in 0.5 M Na2SO4 solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as VRHE) than BiVO4 film (0.12 mA/㎠ at 1.23 VRHE). Moreover, Al2O3 coating on the Mo:BiVO4 film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 VRHE) than the Mo:BiVO4 film (0.86 mA/㎠ at 1.23 VRHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO4 film and Al2O3/Mo:BiVO4 film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (VFB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al2O3 coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al2O3 layer.

Acknowledgement

Supported by : Korea Basic Science Institute, National Research Foundation of Korea (NRF)

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