Asymmetric-Coordinated Indium Single Atoms for Highly Selective Photocatalytic CO₂ Reduction

Abstract

Photocatalytic CO₂ reduction involves multiple proton-coupled and multi-electron transfers, leading to a plethora of reaction pathways and consequently unpredictable products. The unique electronic structure and unsaturated coordination environment of single-atom photocatalysts can influence the reaction pathways of CO₂ photoreduction, enhancing the yield of a target product. Herein, we rationally design the In single-atom photocatalyst (In-NTO) containing isolated In^δ+–N₃O₂ atomic interface sites for highly efficient and selective CO₂-to-CO photoreduction. This distinctive atomic configuration not only reduces the overall activation energy barrier but also transforms the key *CO desorption step from an endoergic to an exoergic one, thereby altering the reaction pathway to selectively produce CO rather than CH₄. Consequently, the 0.25 wt% In-NTO exhibits high selectivity (95.9%) for photocatalytic CO₂-to-CO conversion, with a rate of 6.34 µmol g⁻¹ h⁻¹. This work offers a novel strategy for modulating the reactivity and product selectivity of photocatalytic CO₂ reduction toward desired products by constructing single-atom sites with heteroatomic coordination.

Keywords

asymmetric coordination / CO₂ photoreduction / promoting *CO desorption / selectivity CO production / single-atom photocatalyst

References

[1] Z. Jiang, X. Xu, Y. Ma, et al., “Filling Metal-Organic Framework Mesopores With TiO₂ for CO₂ Photoreduction,” Nature 586, no. 7830 (2020): 549–554.

[2] J. J. Leung, J. Warnan, K. H. Ly, et al., “Solar-Driven Reduction of Aqueous CO₂ With a Cobalt Bis(Terpyridine)-Based Photocathode,” Nature Catalysis 2, no. 4 (2019): 354–365.

[3] J. Li, H. Huang, W. Xue, et al., “Self-Adaptive Dual-Metal-Site Pairs in Metal-Organic Frameworks for Selective CO₂ Photoreduction to CH₄,” Nature Catalysis 4, no. 8 (2021): 719–729.

[4] L. Wang, B. Zhu, J. Zhang, J. B. Ghasemi, M. Mousavi, and J. Yu, “S-Scheme Heterojunction Photocatalysts for CO₂ Reduction,” Matter 5, no. 12 (2022): 4187–4211.

[5] G. Ding, C. Li, L. Chen, and G. Liao, “Porphyrin-Based Metal–Organic Frameworks for Photo(Electro)Catalytic CO₂ Reduction,” Energy & Environmental Science 17, no. 15 (2024): 5311–5335.

[6] J. Li, C. Cao, X. Zhang, et al., “Tuning Oxygen Vacancies by Construction of a SiO₂@TiO₂ Core−Shell Composite Structure for Boosting Photocatalytic CO₂ Reduction Towards CH₄,” Carbon Energy 7, no. 4 (2025): e700.

[7] J. Wu, J. Zhu, W. Fan, et al., “Selective Photoreduction of CO₂ to CH₄ Triggered by Metal-Vacancy Pair Sites,” Nano Letters 24, no. 2 (2024): 696–702.

[8] Y. He, S. Dai, J. Sheng, et al., “In Situ Fabrication of Atomically Adjacent Dual-Vacancy Sites for Nearly 100% Selective CH₄ Production,” Proceedings of the National Academy of Sciences of the United States of America 121, no. 25 (2024): e2322107121.

[9] Y. X. Pan, Y. You, S. Xin, et al., “Photocatalytic CO₂ Reduction by Carbon-Coated Indium-Oxide Nanobelts,” Journal of the American Chemical Society 139, no. 11 (2017): 4123–4129.

[10] J. Low, L. Zhang, T. Tong, B. Shen, and J. Yu, “TiO₂/MXene Ti₃C₂ Composite With Excellent Photocatalytic CO₂ Reduction Activity,” Journal of Catalysis 361 (2018): 255–266.

[11] C. B. Hiragond, S. Biswas, N. S. Powar, et al., “Surface-Modified Ag@Ru-P25 for Photocatalytic CO₂ Conversion With High Selectivity over CH₄ Formation at the Solid-Gas Interface,” Carbon Energy 6, no. 1 (2024): e386.

[12] F. Xu, K. Meng, B. Cheng, S. Wang, J. Xu, and J. Yu, “Unique S-Scheme Heterojunctions in Self-Assembled TiO₂/CsPbBr₃ Hybrids for CO₂ Photoreduction,” Nature Communications 11, no. 1 (2020): 4613.

[13] X. Li, Y. Sun, J. Xu, et al., “Selective Visible-Light-Driven Photocatalytic CO₂ Reduction to CH₄ Mediated by Atomically Thin CuIn₅S₈ Layers,” Nature Energy 4, no. 8 (2019): 690–699.

[14] J. Fu, K. Jiang, X. Qiu, J. Yu, and M. Liu, “Product Selectivity of Photocatalytic CO₂ Reduction Reactions,” Materials Today 32 (2020): 222–243.

[15] C. Ban, Y. Wang, Y. Feng, et al., “Photochromic Single Atom Ag/TiO₂ Catalysts for Selective CO₂ Reduction to CH₄,” Energy & Environmental Science 17, no. 2 (2024): 518–530.

[16] X. X. Chang, T. Wang, and J. L. Gong, “CO₂ Photo-Reduction: Insights into CO₂ Activation and Reaction on Surfaces of Photocatalysts,” Energy & Environmental Science 9, no. 7 (2016): 2177–2196.

[17] W. Gao, H. Chi, Y. Xiong, J. Ye, Z. Zou, and Y. Zhou, “Comprehensive Insight into Construction of Active Sites Toward Steering Photocatalytic CO₂ Conversion,” Advanced Functional Materials 34 (2023): 2312056.

[18] J. Liang, H. Zhang, Q. Song, et al., “Modulating Charge Separation of Oxygen-Doped Boron Nitride With Isolated CO Atoms for Enhancing CO₂-to-CO Photoreduction,” Advanced Materials 36, no. 1 (2023): 2303287.

[19] X. Shang, X. Yang, G. Liu, T. Zhang, and X. Su, “A Molecular View of Single-Atom Catalysis Toward Carbon Dioxide Conversion,” Chemical Science 15, no. 13 (2024): 4631–4708.

[20] X. Jin, Y. Xu, X. Zhou, et al., “Single-Atom Fe Triggers Superb CO₂ Photoreduction on a Bismuth-Rich Catalyst,” ACS Materials Letters 3, no. 4 (2021): 364–371.

[21] W. Xie, Y. Liu, X. Zhang, et al., “Asymmetric Cu−N−La Species Enabling Atomic-Level Donor-Acceptor Structure and Favored Reaction Thermodynamics for Selective CO₂ Photoreduction to CH₄,” Angewandte Chemie International Edition 63, no. 5 (2023): e202314384.

[22] G. Wang, C. T. He, R. Huang, J. Mao, D. Wang, and Y. Li, “Photoinduction of Cu Single Atoms Decorated on UiO-66-NH₂ for Enhanced Photocatalytic Reduction of CO₂ to Liquid Fuels,” Journal of the American Chemical Society 142, no. 45 (2020): 19339–19345.

[23] H. Zhang, Y. Wang, S. Zuo, W. Zhou, J. Zhang, and X. W. D. Lou, “Isolated Cobalt Centers on W₁₈O₄₉ Nanowires Perform as a Reaction Switch for Efficient CO₂ Photoreduction,” Journal of the American Chemical Society 143, no. 5 (2021): 2173–2177.

[24] Y. Jiang, Y. Sung, C. Choi, et al., “Single-Atom Molybdenum−N₃ Sites for Selective Hydrogenation of CO₂ to CO,” Angewandte Chemie International Edition 61, no. 37 (2022): e202203836.

[25] X. Sun, L. Sun, G. Li, et al., “Phosphorus Tailors the d-Band Center of Copper Atomic Sites for Efficient CO₂ Photoreduction Under Visible-Light Irradiation,” Angewandte Chemie International Edition 61, no. 38 (2022): e202207677.

[26] Y. Gao, J. Ge, J. Zhang, et al., “Asymmetrically Coordinated Main Group Atomic In-S₁N₃ Interface Sites for Promoting Electrochemical CO₂ Reduction,” Nano Research 17, no. 6 (2024): 5011–5021.

[27] C. Ding, X. Lu, B. Tao, et al., “Interlayer Spacing Regulation by Single-Atom Indium^δ+-N₄ on Carbon Nitride for Boosting CO₂/CO Photo-Conversion,” Advanced Functional Materials 33, no. 35 (2023): 2302824.

[28] X. H. Jiang, L. S. Zhang, H. Y. Liu, et al., “Silver Single Atom in Carbon Nitride Catalyst for Highly Efficient Photocatalytic Hydrogen Evolution,” Angewandte Chemie International Edition 59, no. 51 (2020): 23112–23116.

[29] S. Wang, L. Pan, J. J. Song, et al., “Titanium-Defected Undoped Anatase TiO₂ With P-Type Conductivity, Room-Temperature Ferromagnetism, and Remarkable Photocatalytic Performance,” Journal of the American Chemical Society 137, no. 8 (2015): 2975–2983.

[30] C. Mao, J. Wang, Y. Zou, et al., ““Hydrogen Spillover to Oxygen Vacancy of TiO_2-xH_y/Fe: Breaking the Scaling Relationship of Ammonia Synthesis,” Journal of the American Chemical Society 142, no. 41 (2020): 17403–17412.

[31] Y. Cao, D. Chen, Y. Meng, S. Saravanamurugan, and H. Li, “Visible-Light-Driven Prompt and Quantitative Production of Lactic Acid From Biomass Sugars Over a N-TiO₂ Photothermal Catalyst,” Green Chemistry 23, no. 24 (2021): 10039–10049.

[32] D. Liu, L. Jiang, D. Chen, et al., “Twin S-Scheme g-C₃N₄/CuFe₂O₄/ZnIn₂S₄ Heterojunction With a Self-Supporting Three-Phase System for Photocatalytic CO₂ Reduction: Mechanism Insight and DFT Calculations,” ACS Catalysis 14, no. 7 (2024): 5326–5343.

[33] C. Jin, C. Wang, T. Huang, T. Chen, and F. Wang, “Hollow Amorphous N-Doped TiO₂ Microspheres With Uniform Shell Thickness and High Carrier Separation Efficiency for Photocatalytic of High-Concentration Cr(VI),” Optical Materials 159 (2025): 116516.

[34] N. L. Reddy, S. Emin, V. D. Kumari, and S. Muthukonda Venkatakrishnan, “CuO Quantum Dots Decorated TiO₂ Nanocomposite Photocatalyst for Stable Hydrogen Generation,” Industrial & Engineering Chemistry Research 57, no. 2 (2018): 568–577.

[35] N. Yuan, J. Zhang, S. Zhang, et al., “What Is the Transfer Mechanism of Photoexcited Charge Carriers for g-C₃N₄/TiO₂ Heterojunction Photocatalysts? Verification of the Relative p–n Junction Theory,” Journal of Physical Chemistry C 124, no. 16 (2020): 8561–8575.

[36] L. Pan, S. Wang, J. Xie, L. Wang, X. Zhang, and J.-J. Zou, “Constructing TiO₂ p-n Homojunction for Photoelectrochemical and Photocatalytic Hydrogen Generation,” Nano Energy 28 (2016): 296–303.

[37] C. Zhang, H. Hua, J. Liu, et al., “Enhanced Photocatalytic Activity of Nanoparticle-Aggregated Ag-AgX (X = Cl, Br)@TiO₂ Microspheres Under Visible Light,” Nano-Micro Letters 9, no. 4 (2017): 49.

[38] H. Li, J. Li, and Y. Huo, “Highly Active TiO₂N Photocatalysts Prepared by Treating TiO₂ Precursors in NH₃/Ethanol Fluid Under Supercritical Conditions,” Journal of Physical Chemistry B 110, no. 4 (2006): 1559–1565.

[39] M. Sathish, B. Viswanathan, R. P. Viswanath, and C. S. Gopinath, “Synthesis, Characterization, Electronic Structure, and Photocatalytic Activity of Nitrogen-Doped TiO₂ Nanocatalyst,” Chemistry of Materials 17, no. 25 (2005): 6349–6353.

[40] H. Shang, T. Wang, J. Pei, et al., “Design of a Single-Atom Indium^δ+-N₄ Interface for Efficient Electroreduction of CO₂ to Formate,” Angewandte Chemie International Edition 59, no. 50 (2020): 22465–22469.

[41] H. Shi, H. Wang, Y. Zhou, et al., “Atomically Dispersed Indium-Copper Dual-Metal Active Sites Promoting C−C Coupling for CO₂ Photoreduction to Ethanol,” Angewandte Chemie International Edition 61, no. 40 (2022): e202208904.

[42] W. Chen, H. Jin, F. He, P. Cui, C. Cao, and W. Song, “Dynamic Evolution of Nitrogen and Oxygen Dual-Coordinated Single Atomic Copper Catalyst During Partial Oxidation of Benzene to Phenol,” Nano Research 15, no. 4 (2021): 3017–3025.

[43] Y. Shen, C. Ren, L. Zheng, et al., “Room-Temperature Photosynthesis of Propane From CO₂ With Cu Single Atoms on Vacancy-Rich TiO₂,” Nature Communications 14, no. 1 (2023): 1117.

[44] M. Xing, Y. Zhou, C. Dong, et al., “Modulation of the Reduction Potential of TiO_2-x by Fluorination for Efficient and Selective CH₄ Generation From CO₂ Photoreduction,” Nano Letters 18, no. 6 (2018): 3384–3390.

[45] Y. Yang, L.-C. Yin, Y. Gong, et al., “An Unusual Strong Visible-Light Absorption Band in Red Anatase TiO₂ Photocatalyst Induced by Atomic Hydrogen-Occupied Oxygen Vacancies,” Advanced Materials 30, no. 6 (2018): 1704479.

[46] H.-N. Wang, Y.-H. Zou, H.-X. Sun, Y. Chen, S.-L. Li, and Y.-Q. Lan, “Recent Progress and Perspectives in Heterogeneous Photocatalytic CO₂ Reduction Through a Solid–Gas Mode,” Coordination Chemistry Reviews 438 (2021): 213906.

[47] F. Tian, M. Zhu, X. Sun, and X. Yan, “Self-Assembled Zn_1–xO/TiO₂ Nanocomposite as a Novel p–n Heterojunction for Selective CO₂-to-CO Photoreduction,” ACS Applied Nano Materials 6, no. 16 (2023): 15213–15223.

[48] J. Di, C. Zhu, M. Ji, et al., “Defect-Rich Bi₁₂O₁₇Cl₂ Nanotubes Self-Accelerating Charge Separation for Boosting Photocatalytic CO₂ Reduction,” Angewandte Chemie International Edition 57, no. 45 (2018): 14847–14851.

[49] C. Li, H. Lu, G. Ding, et al., “Interfacial Coordination Bonds Accelerate Charge Separation for Unprecedented Hydrogen Evolution over S-Scheme Heterojunction,” Chinese Journal of Catalysis 65 (2024): 174–184.

[50] H. Zhu, L. Gou, C. Li, et al., “Dual Interfacial Electric Fields in Black Phosphorus/MXene/MBene Enhance Broad-Spectrum Carrier Migration Efficiency of Photocatalytic Devices,” Device 2, no. 3 (2024): 100283.

[51] L. Liu, H. Huang, F. Chen, et al., “Cooperation of Oxygen Vacancies and 2D Ultrathin Structure Promoting CO₂ Photoreduction Performance of Bi₄Ti₃O₁₂,” Science Bulletin 65, no. 11 (2020): 934–943.

[52] C. Ban, Y. Duan, Y. Wang, et al., “Isotype Heterojunction-Boosted CO₂ Photoreduction to CO,” Nano-Micro Letters 14, no. 1 (2022): 74.

[53] Y. Cao, L. Guo, M. Dan, et al., “Modulating Electron Density of Vacancy Site by Single Au Atom for Effective CO₂ Photoreduction,” Nature Communications 12, no. 1 (2021): 1675.

[54] Y. Li, B. Li, D. Zhang, L. Cheng, and Q. Xiang, “Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO₂ Reduction With Nearly 100% CO Selectivity,” ACS Nano 14, no. 8 (2020): 10552–10561.

[55] J. Di, X. Zhao, C. Lian, et al., “Atomically-Thin Bi₂MoO₆ Nanosheets With Vacancy Pairs for Improved Photocatalytic CO₂ Reduction,” Nano Energy 61 (2019): 54–59.

[56] W. Bi, Y. Hu, H. Jiang, L. Zhang, and C. Li, “Revealing the Sudden Alternation in Pt@h-BN Nanoreactors for Nearly 100% CO₂-to-CH₄ Photoreduction,” Advanced Functional Materials 31, no. 29 (2021): 2010780.

[57] T. Takayama, K. Tanabe, K. Saito, A. Iwase, and A. Kudo, “The KCaSrTa₅O₁₅ Photocatalyst With Tungsten Bronze Structure for Water Splitting and CO₂ Reduction,” Physical Chemistry Chemical Physics 16, no. 44 (2014): 24417–24422.

[58] S. Mo, X. Zhao, S. Li, et al., “Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO₂ Reduction,” Angewandte Chemie International Edition 62, no. 50 (2023): e202313868.

[59] S. Hu, P. Qiao, X. Yi, et al., “Selective Photocatalytic Reduction of CO₂ to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride,” Angewandte Chemie International Edition 62, no. 26 (2023): e202304585.

[60] M. Jiang, C. Li, K. Huang, et al., “Tuning W₁₈O₄₉/Cu₂O {111} Interfaces for the Highly Selective CO₂ Photocatalytic Conversion to CH₄,” ACS Applied Materials & Interfaces 12, no. 31 (2020): 35113–35119.

RIGHTS & PERMISSIONS

2026 The Author(s). Carbon Energy published by Wenzhou University and John Wiley & Sons Australia, Ltd.