Crucial Effect of Ti-H Species Generated in the Visible-Light-Driven Transformations: Slowed-Down Proton-Coupled Electron Transfer

Yuhan Lin; Yan Yan; Wei Peng; Xiaofeng Qiao; Di Huang; Hongwei Ji; Chuncheng Chen; Wanhong Ma; Jincai Zhao

doi:10.1021/acs.jpclett.0c01196

Crucial Effect of Ti-H Species Generated in the Visible-Light-Driven Transformations: Slowed-Down Proton-Coupled Electron Transfer

J Phys Chem Lett. 2020 May 21;11(10):3941-3946. doi: 10.1021/acs.jpclett.0c01196. Epub 2020 May 6.

Authors

Yuhan Lin^{1

2}, Yan Yan³, Wei Peng^{1

2}, Xiaofeng Qiao^{1

2}, Di Huang^{1

2}, Hongwei Ji^{1

2}, Chuncheng Chen^{1

2}, Wanhong Ma^{1

2}, Jincai Zhao^{1

2}

Affiliations

¹ Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
² University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
³ Jiangsu University, Zhenjiang 212013, P. R. China.

PMID: 32353238
DOI: 10.1021/acs.jpclett.0c01196

Abstract

Despite the fact that proton-coupled electron transfer (PCET) has been hypothesized to play a pivotal role in the power conversion efficiency (PCE) of TiO₂-based solar-energy applications, the specific relationship between the intrinsic nature of visible-light (Vis)-driven PCET reactions and limited PCE gains has not yet been well revealed. Here we studied the detailed kinetics of reactions between various alcohols and radicals (^tBu₃ArO^•/TEMPO) on a TiO₂ photocatalyst under dye-sensitization Vis irradiation versus direct ultraviolet (UV) irradiation. We found that the rates of Vis-driven reactions were much slower than those of UV-driven reactions under identical light intensity. A similar phenomenon was observed under the off-line dark-reaction conditions in which TiO₂ was prereduced by alcohols. The rapid formation and difficult breakage of the stable "Ti-H" intermediate were proposed to account for the slowed-down PCET effect. This finding revealed an inherent bottleneck in Vis-driven energy conversion applications.