Long Time In-situ Raman Observation of the Cu Cathode Surface without Pretreatment during CO2 Electrochemical Reduction
Katsushi Fujii a, Kayo Koike a, Kei Morishita a, Eri Torikai b, Jun Matsumoto b, Dai Takeda b, Ryuhei Nakamura c, Satoshi Wada a
a RIKEN Center for Advanced Photonics
b Chiyoda Corporation
c RIKEN Center for Sustainable Resource Science
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#SolCat19. (Photo)electrocatalysis for sustainable carbon utilization: mechanisms, methods, and reactor development
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Matthew Mayer and Ludmilla Steier
Poster, Katsushi Fujii, 405
Publication date: 18th July 2019

              The reduction of CO2 to useful aliphatic compounds is a promising technology to establish a carbon recycle society. Although electrochemical CO2 reduction has not been established, the electrochemical reduction has been considered to be an attracting technique due to its possibility of mass production and C-C double bond formation. Well-known cathode material to generate aliphatic compounds is Cu. However, the Cu cathode has problems of not only produced material non-controllability but also the time-dependent change of the product ratio. This time-dependent behavior is believed to be an indication of the change of their reaction environments especially at the interface of the KHCO3 aqueous electrolyte and Cu cathode. In-situ acquisition of Raman spectra is expected to evaluate this changing of the interface structure.

The in-situ Raman observation of the long-time and real current density operation of a Cu electrode is difficult because the operation is usually performed in a micro-Raman system. That is, the reactor for the micro Raman system is required to be able to operate under the objective lens in the optical microscope. Reproducing the real reaction circumstances for the micro Raman system is difficult due to the space limitation. In this study, the conventional Raman system was used in order to be set close to the real operation condition. As a result, the long time and real current density operation were available even under the Raman observation.

Conventional Cu cathodes without pre-treatment were evaluated by the conventional Raman system. It is reported that Cu oxides rapidly reduced to metallic Cu due to the strong reduced condition (around -1.5 to -1.6 V vs Ag/AgCl at pH 6 to 7) [1,2]. The Raman peak at 525 cm-1 assigned as Cu2O was clearly observed during the electrochemical reduced reaction in the present study. The peak at 525 cm-1 was observed after 210 min from the reduction started for one of the samples, and the peak was observed from the beginning for the other sample. These results probably show the Cu surface is very sensitive to the starting surface conditions.

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