Proceedings of MATSUS Spring 2024 Conference (MATSUS24)
DOI: https://doi.org/10.29363/nanoge.matsus.2024.355
Publication date: 18th December 2023
Electro and photochemical CO2 reduction (CO2R) is the quintessence of modern-day sustainable research. We report our studies on the electro and photoinduced interfacial charge transfer occurring in nanocrystalline mesoporous TiO2 film and two TiO2/Iron porphyrin hybrid films (meso-aryl and b-pyrrole substituted porphyrins, respectively) under CO2R conditions. We used Transient Absorption Spectroscopy (TAS) to demonstrate that under 355 nm laser excitation and an applied voltage bias (0 to -0.8 V vs. Ag/AgCl), the TiO2 film exhibited a diminution in the transient absorption (at -0.5 V by 35%), as well as a reduction of the lifetime of the photogenerated electrons (at -0.5 V by 50%) when the experiments were conducted under CO2 atmosphere changing from inert N2. The TiO2/Iron porphyrin films showed faster charge recombination kinetics, featuring 100-fold more rapid transient signal decay than the TiO2 film. The electro, photo, and photoelectrochemical CO2R performance of the TiO2 and TiO2/Iron porphyrin films are evaluated within the bias range of -0.5 to -1.8 V vs. Ag/AgCl. The bare TiO2 film produced CO and CH4, as well as H2, depending on the applied voltage bias.
In contrast, the TiO2/Iron porphyrins films showed the exclusive formation of CO (100% selectivity) under identical conditions. During the CO2R, gain in the overpotential values is obtained under the light irradiation conditions. This finding indicated a direct transfer of the photogenerated electrons from the film to absorbed CO2 molecules and a decreased decay of the TAS signals. In the TiO2/Iron porphyrin films, we identified the interfacial charge recombination processes between the oxidized iron-porphyrin and the electrons of the TiO2 conduction band. These competitive processes are considered responsible for the diminution of direct charge transfer between the film and the adsorbed CO2 molecules, explaining the moderate performances of the hybrid films for the CO2R.
EP is thankful to MCIN and ESF for a predoctoral grant (PRE2020-092525), to NEFERTITI (H2020) project for a postdoctoral fellowship (Grant agreement ID: 101022202) and thanks to MCIN/AEI/10.13039/501100011033 for a Juan de la Cierva-Incorporación fellowship (IJC2019-042363-I). Funding from MINECO (project PID2019-109389RB-I00) and SGR-AGAUR (project 2021SGR01261) is also acknowledged. E.P. gratefully acknowledges financial support from ICIQ, MINECO, and ICREA.
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