Concentration-Mediated Band Gap Reduction of Bi2MoO6 Photoanodes Prepared by Bi3+ Cation Insertions into Anodized MoO3 Thin Films : Structural, Optical, and Photoelectrochemical Properties

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review

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Author(s)

Detail(s)

Original languageEnglish
Pages (from-to)3955-3964
Journal / PublicationACS Applied Energy Materials
Volume1
Issue number8
Early online date12 Jul 2018
Publication statusPublished - 27 Aug 2018
Externally publishedYes

Abstract

A secondary cation insertion technique to fabricate ternary Bi2MoO6 thin films with reduced optical band gaps and shallow valence bands by the controllable insertion of Bi3+ cations into anodized MoO3 thin films has been established. Near-complete conversion of the MoO3 thin film to a low-temperature-phase γ(L)-Bi2MoO6 thin film was achieved when the MoO3 thin films were subject to hydrothermal treatment in a low Bi(NO3)3·5H2O solution concentration. In contrast, a bilayered Bi2MoO6/MoO3 thin film photoelectrode comprising predominantly a high-temperature-phase γ(H)-Bi2MoO6 oxide-electrolyte interface top region and a MoO3 oxide-collector interface bottom region was formed when a high Bi(NO3)3·5H2O solution concentration was utilized. UV-vis spectroscopy shows both the γ(L)-Bi2MoO6 (Eg = 2.7 eV) and γ(H)-Bi2MoO6 (Eg = 3.05 eV) thin films exhibit smaller band gaps than MoO3 (Eg = 3.4 eV). For γ(L)-Bi2MoO6, the reduction in optical band gap was attributed to the formation of a higher-lying O 2p valence band maximum while, for the γ(H)-Bi2MoO6 thin film, hybridization of the Bi 6s orbitals with the O 2p valence orbitals lowers the potential of the valence band maximum, leading to the reduced band gap. Overall, the Bi2MoO6 thin films with the highest γ(L)-Bi2MoO6 concentration exhibited the highest photocurrent density. The photocurrent enhancement can be attributed to two main reasons: first, the trilayer Bi2MoO6/MoO3 heterostructure obtained from the direct thin film assembly enables a smooth percolation of photoexcited charges from the surface generation sites to the charge collection sites at the Mo substrate, minimizing charge recombination losses; second, the MoO6 octahedra-coordinated γ(L)-Bi2MoO6 possesses a wide conduction band enabling fast separation and migration of delocalized charges. The secondary cation insertion technique has potential as a universal method to prepare complex oxides with narrow band gaps and shallow valence bands from insertion-type oxides for solar energy applications.

Research Area(s)

  • Bi2MoO6, MoO3, photocatalysis, photoelectrochemical water splitting, solar energy conversion, thin film

Citation Format(s)

Concentration-Mediated Band Gap Reduction of Bi2MoO6 Photoanodes Prepared by Bi3+ Cation Insertions into Anodized MoO3 Thin Films : Structural, Optical, and Photoelectrochemical Properties. / Lou, Shi Nee; Amal, Rose; Scott, Jason; Ng, Yun Hau.

In: ACS Applied Energy Materials, Vol. 1, No. 8, 27.08.2018, p. 3955-3964.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalNot applicablepeer-review