Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties
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-temperatur...
| Main Authors: | , , , |
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| Format: | Journal Article |
| Language: | English |
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2021
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| Online Access: | https://hdl.handle.net/10356/151595 |
| _version_ | 1826127019850596352 |
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| author | Lou, Shi Nee Amal, Rose Scott, Jason Ng, Yun Hau |
| author2 | School of Materials Science and Engineering |
| author_facet | School of Materials Science and Engineering Lou, Shi Nee Amal, Rose Scott, Jason Ng, Yun Hau |
| author_sort | Lou, Shi Nee |
| collection | NTU |
| description | 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. |
| first_indexed | 2024-10-01T07:01:55Z |
| format | Journal Article |
| id | ntu-10356/151595 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T07:01:55Z |
| publishDate | 2021 |
| record_format | dspace |
| spelling | ntu-10356/1515952021-06-28T07:27:32Z 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 School of Materials Science and Engineering Engineering::Materials Bi₂MoO₆ Solar Energy Conversion 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. This work was financially supported by the Australian Research Council under the Laureate Fellowship Scheme - FL140100081. 2021-06-28T07:27:31Z 2021-06-28T07:27:31Z 2018 Journal Article Lou, S. N., Amal, R., Scott, J. & Ng, Y. H. (2018). Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties. ACS Applied Energy Materials, 1(8), 3955-3964. https://dx.doi.org/10.1021/acsaem.8b00675 2574-0962 0000-0001-9561-4918 0000-0003-2395-2058 0000-0001-9142-2126 https://hdl.handle.net/10356/151595 10.1021/acsaem.8b00675 2-s2.0-85064760580 8 1 3955 3964 en ACS Applied Energy Materials © 2018 American Chemical Society. All rights reserved. |
| spellingShingle | Engineering::Materials Bi₂MoO₆ Solar Energy Conversion Lou, Shi Nee Amal, Rose Scott, Jason Ng, Yun Hau Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title | Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title_full | Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title_fullStr | Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title_full_unstemmed | Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title_short | Concentration-mediated band gap reduction of Bi₂MoO₆ photoanodes prepared by Bi³⁺ cation insertions into anodized MoO₃ thin films : structural, optical, and photoelectrochemical properties |
| title_sort | concentration mediated band gap reduction of bi₂moo₆ photoanodes prepared by bi³⁺ cation insertions into anodized moo₃ thin films structural optical and photoelectrochemical properties |
| topic | Engineering::Materials Bi₂MoO₆ Solar Energy Conversion |
| url | https://hdl.handle.net/10356/151595 |
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