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Identifying the key obstacle in photocatalytic oxygen evolution on rutile TiO2

Abstract

As the bottleneck in photocatalytic water splitting, the oxygen evolution reaction (OER) has drawn huge attention, but its efficiency still falls short of expectations. A widely accepted speculation is that the catalysts’ activity is insufficient (high reaction barriers need to be overcome). Here, we develop a first-principles method to investigate the photocatalytic OER at the water/TiO2(110) interface. A full mechanism uncovering the importance of radicals is determined. Kinetic analysis further enables to quantitatively estimate each possible obstacle in the process. We demonstrate unambiguously that the rate-determining factor of the OER varies with the concentration of surface-reaching photoholes (Ch+). Under experimental conditions, the intrinsic catalytic activity of TiO2(110) does not represent the main obstacle, but all steps involving the photoholes are slow due to their low concentrations. This suggests that the key to enhance the OER efficiency is to increase Ch+ before Ch+ reaches the estimated threshold (Ch+ = ~10−4).

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Fig. 1: Schematic of the photocatalytic OER at the water/TiO2 interface.
Fig. 2: Energy profiles of possible water dissociation pathways.
Fig. 4: Energy profiles of O–O coupling reactions among various surface radicals.
Fig. 3: Proposed mechanism (dual pathways) and energy profiles for the photocatalytic OER.
Fig. 5: TOF as a function of the hole concentration from microkinetic analyses.

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Acknowledgements

D.W. thanks the Chinese Scholarship Council for financial support for living abroad and P.H. thanks the Chinese Government for support from the “Thousands Talents” program. This work was financially supported by National Natural Science Foundation of China (21333003, 21421004, 21622305), Young Elite Scientist Sponsorship Program by the China Association for Science and Technology (YESS20150131), The Shanghai ShuGuang project (17SG30), and the Fundamental Research Funds for the Central Universities (WJ616007).

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P.H. and H.-F.W. conceived the project and contributed to the design of the calculations and analyses of the data. D.W. carried out most of the calculations and wrote the first draft of the paper. T.S. and D.W. conducted the tests of the MPA-MD method. J.C. wrote the kinetic code and contributed to the analyses of data. All the authors discussed the results and commented on the manuscript.

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Correspondence to Hai-Feng Wang or P. Hu.

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Wang, D., Sheng, T., Chen, J. et al. Identifying the key obstacle in photocatalytic oxygen evolution on rutile TiO2. Nat Catal 1, 291–299 (2018). https://doi.org/10.1038/s41929-018-0055-z

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