Issue 18, 2016

Photoelectrochemical water oxidation using a Bi2MoO6/MoO3 heterojunction photoanode synthesised by hydrothermal treatment of an anodised MoO3 thin film

Abstract

An effective Mo-based ternary oxide Bi2MoO6/MoO3 thin film for photoelectrochemical (PEC) water oxidation was prepared via a simple and direct thin film synthesis route. The synthesis strategy involved subjecting a MoO3 thin film, prepared by anodising a Mo foil, to hydrothermal treatment in the presence of a bismuth salt solution. The new approach removes the need for preformed particles to prepare the film, in turn providing a robust and stable anode for PEC water splitting. X-ray diffraction of the Bi2MoO6/MoO3 thin film revealed the film possessed two photocatalytically active phases of Bi2MoO6: (i) a low temperature phase (γ(L)-Bi2MoO6), and (ii) a high temperature phase (γ(H)-Bi2MoO6). UV-vis spectroscopy showed the optical band gaps of γ(L)-Bi2MoO6 and γ(H)-Bi2MoO6 were 2.75 eV and 3.1 eV, respectively. In contrast, the neat MoO3 thin film had a wider band gap of 3.4 eV. Transforming the surface MoO3 into Bi2MoO6 to construct the Bi2MoO6/MoO3 composite electrode leads to an improvement in photoelectrochemical (PEC) performance. The Bi2MoO6/MoO3 electrode exhibited a 79% enhancement in anodic photocurrent density compared to the unmodified MoO3 thin film under a positive bias of 0.4 V vs. Ag/AgCl. The better performance was attributed to: (i) the narrow optical band gap of Bi2MoO6, which extended the absorption of light by the film into the visible range and (ii) the well-aligned band structure of MoO3 and Bi2MoO6. The Bi2MoO6/MoO3 thin film electrode was subsequently utilised as a photoanode for PEC water splitting. The Bi2MoO6/MoO3 thin film electrode provided close to 100% faradic photocurrent-to-O2 conversion efficiency for PEC water splitting under UV illumination and, importantly, exhibited excellent photostability as a consequence of the unique synthesis method.

Graphical abstract: Photoelectrochemical water oxidation using a Bi2MoO6/MoO3 heterojunction photoanode synthesised by hydrothermal treatment of an anodised MoO3 thin film

Supplementary files

Article information

Article type
Paper
Submitted
25 1 2016
Accepted
11 2 2016
First published
12 2 2016

J. Mater. Chem. A, 2016,4, 6964-6971

Photoelectrochemical water oxidation using a Bi2MoO6/MoO3 heterojunction photoanode synthesised by hydrothermal treatment of an anodised MoO3 thin film

S. N. Lou, J. Scott, A. Iwase, R. Amal and Y. H. Ng, J. Mater. Chem. A, 2016, 4, 6964 DOI: 10.1039/C6TA00700G

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