Strategic Modification of BiVO4 for Improving Photoelectrochemical Water Oxidation Performance

• Published in: Journal of physical chemistry. C 2013-05, Vol.117 (18), p.9104-9112
• Main Authors: Jeong, Hye Won, Jeon, Tae Hwa, Jang, Jum Suk, Choi, Wonyong, Park, Hyunwoong
• Format: Article
• Language: English
• Subjects: Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electrodeposition, electroplating; Electronic transport in condensed matter; Exact sciences and technology; General and physical chemistry; General, apparatus; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Photoconduction and photovoltaic effects; photodielectric effects; Physics; Surface physical chemistry
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp400415m

To improve the photoelectrochemical (PEC) performance of BiVO4, three different modifications (doping, heterojunction, and catalyst deposition) using earth-abundant elements are performed and their effects are compared in a 0.1 M phosphate electrolyte at pH 7 under AM1.5 light (100 mW/cm2). When a hexavalent element (Cr6+, W6+, or Mo6+) is doped at various levels, the Mo6+-doping effect is most significant at 10 atomic % with about two times higher photocurrent generation at the oxygen evolution potential (1.23 VRHE). Such enhancement is attributed to a decrease in charge transfer resistance (R ct) by donor doping, resulting in an approximate 2-fold increase in charge separation efficiency (ηsep) to about 25%. W6+ is less effective than Mo6+, whereas Cr6+ has a detrimental effect. To further improve the charge separation efficiency of Mo6+-doped BiVO4 (Mo-BiVO4), a approximate 600 nm thick WO3 layer is deposited under a similarly thick Mo-BiVO4 layer. This binary heterojunction (WO3/Mo-BiVO4) exhibits ηsep of about 50% along with more than 3 times higher photocurrent generation. On the other hand, an oxygen evolving cobalt-phosphate (Co-Pi) catalyst electrodeposited to Mo-BiVO4 (Mo-BiVO4/Co-Pi) enhances charge injection efficiency (ηinj) from ∼50 to ∼70% at 1.23 V RHE. These two binaries are coupled into a ternary heterojunction (WO3/Mo-BiVO4/Co-Pi) in order to improve the charge transfer efficiencies (ηsep and ηinj). The PEC performance of this ternary is significantly high with photocurrent density of about 2.4 mA/cm2 at 1.23 VRHE (corresponding to the solar-to-hydrogen efficiency of ca. 3%) due to ηsep and ηinj of ∼60 and 90%, respectively.