Real-time Observation of Electron Transfer Mediators in Artificial Photosynthesis
A study conducted by Tomiko M. Suzuki et al. in collaboration with Tokyo University of Science was published in the Chemical Communications and selected as a HOT Article 2025.
Artificial photosynthesis, which uses sunlight and water to convert carbon dioxide (CO2) into useful resources, is a key technology for achieving a carbon-neutral society. To date, our company, in collaboration with Tokyo University of Science, has developed a visible-light-driven CO2 reduction system that operates via a two-step photoexcitation (Z-scheme) mechanism using two photocatalysts and a cobalt (Co) complex, achieving high selectivity (over 95%). The water-soluble Co complex acts as an electron transfer mediator between the photocatalysts; however, its extremely low concentration has limited real-time observation of its valence behavior.
In this study, we directly observed valence state changes of Co ion species during the reaction using operando X-ray absorption spectroscopy at the Toyota beamline of the SPring-8 synchrotron facility. Under light irradiation, the Co complexes shifted the balance between divalent and trivalent states to reach a steady state, enabling continuous CO2 reduction.
This research provides insights that advance the understanding of photocatalytic reaction mechanisms and support the design of more efficient photocatalytic systems.
Title: Direct Observation of An Ionic Cobalt Complex Electron Mediator via Operando X-ray Absorption Spectroscopy in Photocatalytic Z-scheme CO2 reduction with (CuGa)0.3Zn1.4S2 and BiVO4
Authors: Suzuki, M., T., Nonaka, T., Uyama, T., Sakamoto, N., Sekizawa, K., Yamaguchi, Y., Kudo, A., Takeshi Morikawa, T.
Journal Name: Chemical Communications
Published: Nov. 13, 2025
https://doi.org/10.1039/D5CC05617A