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In Situ Optimizing Thin Semiconductor Passive Films of Bismuth Oxides and Sulfides under Visible Light Illumination for Enhanced Photoelectrochemical Performances

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Authors:
Peng Liu
Peng Liu
Peng Liu
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Yun Xie
Yun Xie
Yun Xie
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Wei Zhao
Wei Zhao
Wei Zhao
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Zelin Li at Hunan Normal University
Zelin Li
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Abstract

We report here an in situ method to monitor and optimize formation of thin semiconductor passive films of bismuth oxides and sulfides for enhanced photoelectrochemical performances. It was conducted by cyclic voltammetry under visible light illumination in a mixed solution of Na2SO3 and Na2S. Electrooxidation and sulfurization of Bi electrodes occurred simultaneously during the potential cyclings between -1 V and 0 V (vs. Hg vertical bar Hg2SO4(s)vertical bar K2SO4 (saturated)), and the semiconductor passive film with an appropriate thickness was formed effectively under light illumination. In comparison with the composite film of Bi2S3/Bi2O3 loaded on conductive glass, enhanced photoelectrochemical performances were observed in much wider potential ranges on the prepared semiconductor passive film due to its very compact coverage. Higher anodic photocurrent density was obtained from -1 V to 10 V on the semiconductor passive film prepared under light illumination than in dark, and under galvanostatic operation the anodic potential went back and forth between -1.1 V and 9.8 V rapidly while the visible light illumination was on and off. We expect that these photoelectrochemical characteristics will find applications in photoelectrochemical hydrogen production, photodetectors and photoswitches. (C) 2015 The Electrochemical Society.
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H48 Journal of The Electrochemical Society,163 (2) H48-H52 (2016)
0013-4651/2016/163(2)/H48/5/$33.00 ©The Electrochemical Society
In Situ Optimizing Thin Semiconductor Passive Films of Bismuth
Oxides and Sulfides under Visible Light Illumination for Enhanced
Photoelectrochemical Performances
Peng Liu, Yun Xie, Wei Zhao, and Zelin Liz
Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China),
College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081,
People’s Republic of China
We report here an in situ method to monitor and optimize formation of thin semiconductor passive films of bismuth oxides and
sulfides for enhanced photoelectrochemical performances. It was conducted by cyclic voltammetry under visible light illumination
in a mixed solution of Na2SO3and Na2S. Electrooxidation and sulfurization of Bi electrodes occurred simultaneously during the
potential cyclings between −1Vand0V(vs.Hg|Hg2SO4(s)|K2SO4(saturated)), and the semiconductor passive film with an
appropriate thickness was formed effectively under light illumination. In comparison with the composite film of Bi2S3/Bi2O3loaded
on conductive glass, enhanced photoelectrochemical performances were observed in much wider potential ranges on the prepared
semiconductor passive film due to its very compact coverage. Higher anodic photocurrent density was obtained from −1Vto10
V on the semiconductor passive film prepared under light illumination than in dark, and under galvanostatic operation the anodic
potential went back and forth between −1.1 V and 9.8 V rapidly while the visible light illumination was on and off. We expect that
these photoelectrochemical characteristics will find applications in photoelectrochemical hydrogen production, photodetectors and
photoswitches.
© 2015 The Electrochemical Society. [DOI: 10.1149/2.0711602jes] All rights reserved.
Manuscript submitted September 10, 2015; revised manuscript received October 19, 2015. Published November 20, 2015.
Recently, electrochemical fabrication of Bi-based semiconductor
films for photoelectrochemistry and photocatalysis has attracted in-
creasing attention due to its simplicity, controllability, and low cost.
For example, nanoporous Bi2O3was fabricated by anodization of Bi
at 20 V,1BiVO4films were prepared either by cathodic deposition in a
mixed solution of Bi(NO3)3and VOSO42or by anodic stripping of pre-
electrodeposited Bi in VO43−-containing electrolytes,3nanoflake-like
BiOX (X =Cl−,Br
−and I−) films were obtained by anodization of Bi
in X−-containing solutions4or by cathodic deposition,5Bi2Se3films
were cathodically deposited in a non-aqueous bath,6and urchin-like
Bi(OH)SO4·H2O films were anodically deposited by electrooxidation
of Bi in H2SO4solution.7However, it is not easy to obtain optimized
semiconductor films when the preparation and photoelectrochemical
measurement are conducted separately.
In this work, we report an in situ method to monitor and optimize
the formation of thin semiconductor passive films of bismuth oxides
and sulfides by cyclic voltammetry under visible light illumination
for enhanced photoelectrochemical performances in wide potential
ranges. Although Bi2S3films from anodization of Bi electrodes in
alkaline sulfide solutions were investigated previously,8,9those films
were not optimized, and their photocurrent densities observed in nar-
row potential ranges were very low.
Experimental
Chemicals and synthesis of passive films of bismuth oxides and
sulfides.— All chemicals were of analytical grade and were purchased
from commercial sources without further purification. All solutions
were prepared with Millipore ultrapure water. Electrochemical ex-
periments were performed on a CHI 660C electrochemical station
(Chenhua Instruments, Shanghai, China) in a home-made spectro-
electrochemical cell with three electrodes: a bismuth disk (2.5 mm
diameter) made from bismuth granules (purity≥99.5%) as working
electrode, a platinum ring (12 cm at length, 1 mm in diameter) as
counter electrode and a saturated mercurous sulfate electrode (SMSE)
as reference electrode. Prior to use, the bismuth electrode was pol-
ished with metallographic sandpaper (1200 mesh) and cleaned ultra-
sonically three times in Millipore water. Typically, passive films of
Bi electrodes were prepared in situ by cyclic voltammetry (CV) for
thirty consecutive cycles between −1 V and 0 V at 50 mV s−1in a
zE-mail: lizelin@hunnu.edu.cn
mixed solution of 1 M Na2SO3and 0.2 M Na2S under visible light
illumination.
Characterization.— Surface morphological images, crystalline
phases and surface composition of Bi electrodes were characterized
by a Quanta FEG 250 scanning electron microscope (SEM), X-ray
diffraction (XRD) on a Bruker D8 Discover X-ray diffractometer with
Cu Kαradiation (0.1542 nm) and X-ray photoelectron spectroscopy
(XPS) on a K-Alpha 1063 spectroscope, respectively.
Photoelectrochemical measurements.— Photoelectrochemical
measurements were carried out with the same apparatus and solution
just after finishing the in situ preparation of semiconductor passive
films. A xenon lamp (CHF-XM35-500 W, Beijing Changtuo Co.)
with a UV cutoff filter (λ>420 nm) served as the visible light source
at 100 mW cm−2.
Results and Discussion
Electrochemical behavior of Bi electrode.— The electrochemical
behavior of Bi electrode has been investigated by CV in solutions of
Na2S9and Na2S+NaOH8,10 with different concentrations. It has been
demonstrated that the redox behavior of Bi electrode depends on the
component and concentration of solutions. To our knowledge, no such
work has been performed in mixed solutions of Na2SandNa
2SO3,
which are usually used in photoelectrochemical measurements. Here,
we confirm the redox pairs of Bi electrode with CV in a mixed solution
of 0.2 M Na2S+1MNa
2SO3in a different way from literature8–10
both by varying the upper potential limit and by replacing Na2SO3
with NaOH.
There are three pairs of redox peaks in cyclic voltammograms of
Bi electrodes without light illumination in the mixed solution of 0.2 M
Na2S+1MNa
2SO3(Fig. 1a). The first oxidation peak (A1) around
−1.28 V is very small and somewhat flat due to strong adsorption of
S2−, where metal Bi is slowly oxidized into Bi(III), forming Bi2S3
by combination with S2−.10 However, the corresponding reduction
peak (C1) at −1.53 V is sharp because of accumulation of Bi2S3at
the surface.10 For the second pair of redox peaks, the large broad
oxidation peak (A2) around −0.5 V and the small sharp reduction
peak (C2) at −1.4 V are related to the formation and reduction of
bismuth oxides, respectively.10 Apparently, peak A2 involves more
charge than peak C2, indicating that S2−is also oxidized at peak A2
into S forming polysulfides ions Sn2−.8Therefore, water molecules
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  • Dec 1978
  • J Electroanal Chem
CdS and Bi2S3 films from anodization of the metals in alkaline sulfide solution wereearlier shown to possess the photoelectrochemical and spectral properties of the corresponding n-type crystals, but with lower efficiency in semiconductor-liquid junction solar cells. The formation and removal of these films have been followed by rotating ring-disk electrode (RRDE) voltammetry, under dark and illuminated conditions, to define the regions of sulfide uptake and release, photovoltaic activity, hydroxide participation and mechanism of sulfur generation.
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