Understanding Active Sites in Molecular (Photo)Electrocatalysis through Vibrational Spectroelectrochemistry

Molecularly defined (photo)electrocatalysts have great potential to perform important energy conversion reactions with high efficiency and selectivity. A particular advantage is their modular design, which allows their reactivity to be tailored to a specific reaction. However, to advance their rational development, a deep mechanistic understanding of the catalytic reactions is required. In situ vibrational spectrochemistry, in particular confocal Raman and infrared absorption spectroscopy, is an extremely powerful method to gain deep insights into the structure and reactivity of electrode-immobilized molecular catalytic systems under operando conditions [1]. Since both vibrational spectroscopic techniques have different selection rules, complementary information about the system under operando conditions can be obtained. In my talk, selected research examples will be used to present the different aspects and features of (photo)electrocatalysis that can be visualized using vibrational spectrochemistry. The target systems presented include, on the one hand, porphyrin- and phthalocyanine-based systems for electrocatalytic oxygen and CO2 reduction [2,3] and, on the other hand, conjugated acetylene polymers for photoelectrocatalytic hydrogen evolution [4]. Spectra evaluation under operando conditions allowed us to demonstrate charge separation and ligand binding within these catalysts, identify the active sites during catalysis, and gain insight into the redox properties, reaction intermediates as well as synergistic effects of dual active sites. [1] H. K. Ly, I. M. Weidinger, Chem. Commun. 2021, 57, 2328-2342 [2] T. R. Ramuglia, V. Budhija, K. H. Ly, M. Marquardt, M. Schwalbe, I. M. Weidinger, ChemCatChem, 2021, 13, 3934. [3] H. Zhong, M. Ghorbani-Asl, K. H. Ly, J. Zhang, J. Ge, M. Wang, Z. Liao, D. Makarov, E. Zschech, E. Brunner, I.M. Weidinger, J. Zhang, A. V. Krasheninnikov, S. Kaskel, R. Dong, X. Feng, Nat. Comm. 2020, 11, 1409. [4] M. Borelli, C. J. Querebillo, D. L. Pastoetter, T. Wang, A. Milani, C. Casari, H. K. Ly, F. He, Y. Hou, C. Neumann, A. Turchanin, H. Sun, I. M. Weidinger, X. Feng, Angew. Chemie Int. Ed. 2021, 60 (34), 18876-18881.