Elsevier

Chemical Engineering Journal

Volume 374, 15 October 2019, Pages 1221-1230
Chemical Engineering Journal

Facile photoelectrochemical water oxidation on Co2+-adsorbed BiVO4 thin films synthesized from aqueous solutions

https://doi.org/10.1016/j.cej.2019.06.014Get rights and content

Highlights

  • Organic solvent free ‘Green syntheses’ of BiVO4 applicable in PEC water oxidation.

  • BiVO4 prepared via electrodeposition from aqueous medium and thermal reaction.

  • Co2+ ion is selected as promising oxygen evolution catalyst for water oxidation.

  • Adsorbed Co2+ on BiVO4 surface enhanced the photocurrent to 3.6 from 1.3 mAcm−2.

  • Co2+Adsorbed BiVO4: form more photo-active monoclinic phases, Rct low, ND high.

Abstract

In this study, the organic solvent free ‘green synthesis’ of bismuth vanadate (BiVO4) has been described for its application in photoelectrochemical (PEC) water oxidation. BiVO4 thin films were successfully prepared through electrodeposition of Bi film on the FTO glass substrate from the aqueous bath containing Bi(NO3)3 in presence of K-Na-tartrate and dextrose; followed by thermo-chemical reaction with an aqueous solution of vanadium acetylacetonate (VO(acac)2). XRD & SEM-EDS analyses indicated the formation of scheelite monoclinic BiVO4 with seed-like morphology. UV–visible absorption spectra measured the band gap energy ~ 2.3 eV indicating visible-light activity of the photocatalyst and the Mott-Schottky analysis showed n-type nature of the semiconductor. Highest photocurrent of 1.3 mA cm−2 (at ~1 V vs Ag/AgCl) for water oxidation and 2 mA cm−2 (at ~0.6 V vs Ag/AgCl) for sacrificial (SO32−) oxidation were measured under 35 mW cm−2 illumination using the optimized thin film and the maximum incident photon to current conversion efficiency (IPCE) of 42% was obtained. The enhanced photocurrent in solar-assisted water oxidation is attributed to the formation of well covered and compact film with improved electrical continuity, shown by minimum charge transfer resistance. Adsorption of an optimized amount of Co2+ over the BiVO4 improves its catalytic properties towards oxygen evolution reaction by approximately 2.5 times, with lowering of charge transfer resistance of the material as measured through impedance analysis.

Graphical abstract

Almost 2.5 fold increase in photoelectrochemical water oxidation performance for Co-modified BiVO4 films under UV–vis illumination with significant lowering of charge transfer resistance.

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Introduction

Conversion of solar energy into usable fuels has received significant attention to the scientific community for the past few decades due to ever increasing demand of energy sources by the developed society and continuous depletion of fossil-fuels. Since the Fujishima and Honda described the process of water splitting to generate H2 and O2 through a photoelectrochemical (PEC) cell, the research has been conducted on various semiconductor (SC) materials to improve the efficiency of the process, but an efficient photoanode is still ambiguous [1], [2], [3].

Recently, Bi (III) based binary and ternary metal oxides have been investigated extensively, BiVO4 described as a promising semiconductor electrodes for use in solar-energy conversion [4], [5] which belongs to scheelite-like metal oxide (ABO4) family. It has ferroelectric properties [6] and is promising material for acousto-optical properties [7], [8] as well as ion conductivity [9], nontoxic pigment for ‘brilliant primrose yellow’ and numerous pigment combinations can be achieved based on BiVO4. Kudo et al. reported for the first time that BiVO4 had excellent photocatalytic efficiency for O2 evolution through water splitting in the presence of an aqueous AgNO3 solution and described photo-decomposition [10]. This metal oxide, generally exists as an n-type semiconductor, is non-toxic and composed of earth-abundant elements and can be deposited using scalable and inexpensive methods [11], [12], [13]. It has a relatively small band gap (≤2.5 eV) that can facilitate efficient light absorption [14], [15]; and the valence band edge is sufficiently positive to drive oxygen evolution reaction (OER) [16], [17], [18]. Also, BiVO4 presents three types of crystal systems: monoclinic scheelite-like (s-m) and tetragonal scheelite-like (s-t) structure and a tetragonal zirconia structure (z-t). Among these, the s-m system having a particular crystal structure shows the highest activity for O2 evolution under UV–vis irradiation [19] with a relatively low bandgap of ~2.4 eV [20] and suitable position of the valence band (VB), compared to the water oxidation potential [21].

BiVO4 has been developed through different method of synthesis like chemical [22], [23], [24], hydrothermal route [25], [26], spin-coating [27], microwave assisted [28], solution based method [29], precipitation method [30] as well electrodeposition method [12, [31]]. It has been reported in the literature that the photocatalytic performance of BiVO4 can be improved through the different surface activating agents like Co-Pi, reduced graphene oxide or doped with different metals or non-metals [32], [33], [34]. Domen et al. demonstrated that the SC surface has been modified through the incorporation of NiO layer with CoOX loaded on BiVO4 surface [35].

Despite these advantages, the water-splitting activity for bare BiVO4 photoanode is quite low and the methods to synthesize BiVO4 semiconductors from aqueous bath have been quite limited. Choi et al. demonstrated earlier that the preparation of high-quality Bi electrodes through electrodeposition from aqueous solutions is difficult due to the solubility factor [36]. However, in the present study, we have successfully modified electro-synthesis procedure to prepare elemental Bi films from an aqueous bath, which is converted to BiVO4 using V3+ suspension in water. The objective of this study is to synthesize photo-electrochemically active BiVO4 thin films from ‘organic solvent free’ environment through a simple cost-effective way. Due to the chemically unstable nature of BiVO4 in strong basic and acidic solutions, it has been mainly investigated under neutral (pH ~ 7) conditions [37]. In this work, considerably high PEC performance and current conversion efficiencies were recorded for the water oxidation reaction. Judicious selection of oxygen evolution catalyst (OECs) on light-harvesting semiconductor can lead to significant improvement in PEC performance and herein, we propose the simple dip-coating route using Co2+ solution to improve the efficiency of BiVO4 films towards water oxidation.

In this context, we have made detailed literature survey (as presented in Table S1, SI) citing synthesized BiVO4 from different aqueous bath and Table S2, SI represents the reports devoted on simple Co2+-modified BiVO4 films for PEC applications indicating a limited work dedicated to this area. In this work we report, that presence of an optimized amount of adsorbed Co2+ on BiVO4 surface can enhance the photocurrent to almost three fold (3.6 mA cm−2) at 1 V vs Ag/AgCl, which is highest among the reported data in literature using similar systems.

Section snippets

Materials

The FTO coated conducting glass substrates (Xin Yan Technologies, Hong Kong) were cleaned in ethanol and de-ionized water by subsequent sonication. All the chemicals (of AR grade) like bismuth nitrate, K-Na-tartrate, dextrose anhydrous, vanadium acetylacetonate (VO(acac)2), Co(NO3)2·H2O, sodium sulfate, sodium sulfite were purchased from Merck.

Preparation of deposition bath

The deposition bath was prepared with 2 mM Bi(NO3)3 as Bi3+ ion source in water in presence of 0.05 M K-Na tartrate as complexing agent and 0.1 M

Results and discussion

The primary factors that influence the overall PEC activities of BiVO4 photo-anodes are the surface morphology and crystallinity of the films along with their suitable modifications, variation in ohmic contact with the substrate, change in carrier concentration.

SEM: The surface morphology of the prepared BiVO4 thin films was analyzed through scanning electron microscopy (SEM), as presented in Fig. S1a–h (SI). From the micrographs, it is evident that the surface of the semiconductor films over

Conclusion

The photoelectrochemically active BiVO4 photoanode has been developed via electrodeposition of elemental Bi film followed by thermo-chemical reaction using V-sources. The progress has been made on promoting PEC water oxidation efficiency via loading of the selective amount of Co2+ oxygen evolution catalyst (OEC). Optimization of film growth condition (0.2 mA cm−2 applied current for 10 min of deposition) leads to the formation of BiVO4 film with superior PEC water oxidation behaviour resulting

Acknowledgments

The present work was financially supported by SERB-DST, Govt. of India (File no. SB/S1/PC-042/2013). Financial assistance from DST International division for Indo-Belarus Joint Project (File no. DST/INT/BLR/P-7/2014), and DST, Govt. of West Bengal, (File no. 902(Sanc.)/ST/P/S & T/4G – 1/2013) to the Department of Chemistry, IIEST, Shibpur are gratefully acknowledged. The authors want to express sincere gratitude to their Belorussia Collaborators: Dr. Mikalai V. Malashchonak, Prof. Alexander V. 

References (39)

  • J.D. Bierlein et al.

    Solid State Commun.

    (1975)
  • K. Hirota et al.

    Mater. Res. Bull.

    (1992)
  • T. Lu

    Solid State Ionics

    (1986)
  • S. Hernandez et al.

    Appl. Catal. B: Environ.

    (2016)
  • I. Khan et al.

    Ultrason. Sonochem.

    (2017)
  • S.D. Abraham et al.

    J. Mol. Str.

    (2016)
  • A. Fujishima et al.

    Nature

    (1972)
  • A. Kudo et al.

    Chem. Soc. Rev.

    (2009)
  • M.M. Momeni et al.

    Surf. Eng.

    (2015)
  • C. Bhattacharya et al.

    J. Phys. Chem. C

    (2013)
  • J. Ren et al.

    ACS Appl. Mater. Interfaces

    (2011)
  • C. Manolikas et al.

    Phys. Status Solidi

    (1980)
  • A. Kudo et al.

    Catal. Lett.

    (1998)
  • J.A. Seabold et al.

    J. Am. Chem. Soc.

    (2012)
  • S.K. Pilli et al.

    Energy Environ. Sci.

    (2011)
  • A. Kudo et al.

    J. Am. Chem. Soc.

    (1999)
  • F.F. Abdi et al.

    Nat. Commun.

    (2013)
  • D.K. Zhong et al.

    J. Am. Chem. Soc.

    (2011)
  • A. Iwase et al.

    J. Mater. Chem.

    (2010)
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