(Invited) Dye-Sensitized Molecular Photoelectrodes for CO2 Reduction Using Water as a Reductant

Abstract

Photocatalytic CO2 reduction using visible light and water as a reductant has been one of the important targets for solving global warming problem and shortage of energy and carbon resources. In this presentation, I talk about two projects, i.e., (1) supramolecular photocatalysts with both functions as photosensitizer and catalysts and (2) photocatalytic CO2 reduction coupled to water oxidation.(1) Highly efficient supramolecular photocatalysts for CO2 reduction1-3 Since CO2 is the most oxidized state of carbon, one-electron reduction of CO2 is an extraordinarily high endergonic reaction. From the viewpoints of low-energy light application, the multi-electron reduction of CO2 via chemical reactions promises to be a more valuable process. This is a main reason why both a photosensitizer and a catalyst are required to promote efficient photocatalytic CO2 reduction. We have developed so-called supramolecular photocatalyts that have both the photosensitizer and the catalyst units. This bonding in the supramolecular photocatalysts can accelerate electron transfer between the two units, which improves the performance of the photocatalytic system, especially on the surface of photofunctional solid materials as described below.(2) Molecular photoelectrodes for photocatalytic CO2 reduction with water as a reductant 1,4 The molecular photocatalytic systems have a weakness, i.e., weak oxidation power in the excited state. For practical application, water should be used as an electron donor. For overcoming this problem, we have developed a hybrid system consisting of the supramolecular photocatalyst and semiconductor electrodes. The hybrid photoelectrochemical cell consisting of this hybrid photocathode and n-type semiconductor photoanode induced visible-light-driven CO2 reduction with water as a reductant to generate CO and O2. References “Photocatalytic Systems for CO2 Reduction: Metal-Complex Photocatalysts and Their Hybrids with Photofunctional Solid Materials” Kumagai, H.; Tamaki, Y.; Ishitani, O., Acc. Chem. Res. 2022, 55, 978-990.“Mechanistic study of photocatalytic CO2 reduction using a Ru(II)-Re(I) supramolecular photocatalyst” Kamogawa, K.; Shimoda, Y.; Miyata, K.; Onda, K.; Yamazaki, Y.; Tamaki, Y.; Ishitani, O., Chem. Sci. 2021, 12, 9682-9693.“Supramolecular Photocatalysts for the Reduction of CO2” Tamaki, Y.; Ishitani, O., ACS Cat. 2017, 7, 3394-3409.“Supramolecular photocatalysts fixed on the inside of the polypyrrole layer in dye sensitized molecular photocathodes: application to photocatalytic CO2 reduction coupled with water oxidation. Kuttassery, F.; Kumagai, H.; Kamata, R.; Ebato, Y.; Higashi, M.; Suzuki, H.; Abe, R.; Ishitani, O., Chem. Sci. 2021, 12, 13216-13232. Figure 1