Preparation of Nanoparticle Porous-Structured BiVO4 Photoanodes by a New Two-Step Electrochemical Deposition Method for Water Splitting

SocMan Ho-Kimura,Wasusate Soontornchaiyakul,Yuichi Yamaguchi,Akihiko Kudo

doi:10.3390/catal11010136

SocMan Ho-Kimura, Wasusate Soontornchaiyakul + Show 2 more

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https://doi.org/10.3390/catal11010136

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Abstract

In the synthesis method of a BiVO4 photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO4 particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO4 does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V2O5 among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO4 crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO4 photoanode was 2.2 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm2 illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO3:Rh–BiVO4 photocatalyst sheet prepared by the BiVO4 synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation.

Highlights

Semiconductor photocatalysts and photoelectrodes can potentially be applied to a green technology that offers renewable energy alternatives to fossil fuels
Choi et al developed the two-step BiVO4 synthesis method, which gave an excellent performance for PEC water oxidation [13,15]
In the Choi method, in Step 1, bismuth oxyiodide (BiOI) was formed by electrochemical deposition

Summary

Introduction

Semiconductor photocatalysts and photoelectrodes can potentially be applied to a green technology that offers renewable energy alternatives to fossil fuels. One such technology is solar-driven hydrogen production by photoelectrochemical (PEC) water splitting. During PEC water splitting, hydrogen and oxygen are generated by p- and n-type semiconductor photoelectrodes, respectively. Many n-type semiconductor photoelectrodes, especially the bismuth vanadate (BiVO4 ) photoanode with favourable band edge positions, can be utilised. The photocatalytic effect of BiVO4 on water splitting under visible light was first reported by Kudo et al [4]. Kudo et al reported that scheelite monoclinic phase BiVO4 showed higher visible light activity for water splitting than tetragonal phase BiVO4 [5,6].

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