Infrared Light-Driven CO2 Overall Splitting at Room Temperature Liang Liang, Xiaodong Li, Yongfu Sun, Yuanlong Tan, Xingchen Jiao, Huanxin Ju, Zeming Qi, Junfa Zhu, Yi Xie  Joule  Volume 2, Issue 5, Pages 1004-1016 (May 2018) DOI: 10.1016/j.joule.2018.02.019 Copyright © 2018 Elsevier Inc. Terms and Conditions

Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 1 Characterizations for the Vo-Rich WO3 Atomic Layers (A–D) TEM image (A) and high-resolution TEM image (B; red gridline denotes the lattice disorder); (C) the height profiles corresponding to the AFM image in (D). (E and F) ESR spectra (E) and O 1s XPS spectra (F) for the Vo-rich WO3 atomic layers, Vo-poor WO3 atomic layers, and WO3 atomic layers. According to the O 1S XPS spectra, the atomic ratios of oxygen vacancies and oxygen atoms in Vo-rich and Vo-poor WO3 atomic layers are roughly calculated to be 14.1% and 7.7%, respectively. See also Figures S1–S4. Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 2 Atomistic Models (Left), Calculated Band Structures (Middle), and Density of States (Right) for the Same WO3 Atomic Layer-Based Models (A–C) Atomistsic model (A), calculated band structure (B), and density of states (C) for the WO3 atomic layer slab with three surface oxygen vacancies (the ratio of oxygen vacancies and oxygen atoms is 7.3%.). (D–F) Atomistic model (D), calculated band structure (E), and density of states (F) for the WO3 atomic layer slab with two surface oxygen vacancies (the ratio of oxygen vacancies and oxygen atoms is 4.7%.). (G–I) Atomistic model (G), calculated band structure (H), and density of states (I) for the WO3 atomic layer slab without surface oxygen vacancies. Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 3 Photoexcited Behavior and Experimental Band Structure for the Vo-Rich WO3 Atomic Layers, Vo-Poor WO3 Atomic Layers, and WO3 Atomic Layers (A–E) Optical absorption spectra (A) and the corresponding optical bandgap (B; dashed line at 2,500 nm indicates where data is joined); (C) SRPES valence-band spectra and the corresponding enlarged spectra between −1.0 and 2.0 eV; (D) photoluminescence spectra under the excitation of 785 nm; (E) secondary electron cutoff (Ecutoff) measured by SRPES spectra, where the work function can be calculated by Φ = hν − Ecutoff; hν is the incident photon energy of 40 eV. (F) Scheme of the electronic band structures, in which VB, CB, and IB refer to valence band, conduction band, and intermediate band; note that the presence of the IB band with a wide range of width could help to harvest IR light. See also Figure S5 and Table S1. Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 4 CO2 Photoreduction Properties for the Vo-Rich WO3 Atomic Layers, Vo-Poor WO3 Atomic Layers, and WO3 Atomic Layers (A) CO and O2 formation rates under silicon nitride lamp irradiation as well as at 60°C in the dark. (B) SVUV-PIMS spectrum of the products after 13CO2 photoreduction for the Vo-rich WO3 atomic layers at hν = 14.5 eV. Inset: signals of m/z = 29 (13CO), detected at photon energies, hν = 14.5 eV. (C) Apparent quantum efficiency (%). (D) Cycling curves of CO evolution. (E) CO2 TPD spectra. (F) In situ FTIR spectra for the IR light-driven CO2 reduction process on the Vo-rich WO3 atomic layers. The error bars in (A) and (C) represent the SD of three independent measurements of the same sample. See also Figures S6–S12. Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions

Scheme 1 Schematic Energy Band Diagram for Solar CO2 Overall Splitting into Hydrocarbons and O2 with the Help of H2O Wide-bandgap semiconductors could catalyze CO2 reduction and O2 evolution simultaneously by absorbing UV light that only accounts for 4% of the total light. A few narrow-bandgap semiconductors could also drive CO2 and H2O concurrent splitting under visible light irradiation, while these semiconductors cannot absorb IR light constituting almost 50% of the solar energy due to the principal limitation. The designed intermediate-band semiconductors could potentially harvest IR light to drive CO2 overall splitting with the help of H2O, benefiting from the created intermediate band. VB, CB, and IB denote the valence band, conduction band, and intermediate band, while UV and IR refer to the ultraviolet and infrared, respectively. NHE, normal hydrogen electrode. Joule 2018 2, 1004-1016DOI: (10.1016/j.joule.2018.02.019) Copyright © 2018 Elsevier Inc. Terms and Conditions