Unraveling the Photocatalytic Water Dissociation Pathways on Two-Dimensional Conjugated Polymers

Understanding the water dissociation pathways on polymer photocatalysts is critically important for developing new conjugated polymers toward solar fuel generation by virtue of their diverse bond-forming reactions. Until now, the detailed reaction pathways on the surface active sites of polymer photocatalysts still remain unknown. Herein, we employed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to unravel the water dissociation pathways on two-dimensional 1,3-diyne-linked conjugated polymers synthesized via oxidative coupling of 1,3,5-tris-(4-ethynylphenyl)-benzene and 1,3,5-triethynylbenzene. In addition, we also used quasi in situ X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) to further validate the results obtained from DRIFTS. In this way, several crucial intermediates formed during photocatalytic water splitting were identified and can be correlated to the computational results. It is shown that the water dissociation pathways are different for different polymers, exemplifying the significance of structural control in developing polymer photocatalysts. This study not only provides significant insights into the microscopic processes of the water splitting reaction catalyzed by metal-free polymer photocatalysts but also offers essential principles for future development of metal-free polymer photocatalysts toward solar-to-chemical energy conversion.