Long Period Voltage Oscillations Associated with Reaction Changes between CO2 Reduction and H2 Formation in Zero-Gap-Type CO2 Electrochemical Reactor

• Published in: ACS energy letters Vol. 9; no. 9; pp. 4225 - 4232
• Main Authors: Mikami, Nagisa, Morishita, Kei, Murakami, Takeharu, Hosobata, Takuya, Yamagata, Yutaka, Ogawa, Takayo, Mukouyama, Yoshiharu, Nakanishi, Shuji, Ager, Joel W., Fujii, Katsushi, Wada, Satoshi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.08.2024; American Chemical Society (ACS)
• Subjects: Electrodes; Electrolytes; Evolution reactions; Letter; Oscillation; Salts
• ISSN: 2380-8195; 2380-8195
• DOI: 10.1021/acsenergylett.4c01256

Zero-gap-type reactors with gas diffusion electrodes (GDE) that facilitate the CO2 reduction reaction (CO2RR) are attractive due to their high current density and low applied voltage. These reactors, however, suffer from salt precipitation and anolyte flooding of the cathode, leading to a short lifetime. Here, using a zero-gap reactor with a transparent cathode end plate, we report periodic voltage oscillations under constant current operation. Increases in cell voltages occur at the same time as the reactor switches from the hydrogen evolution reaction (HER) to predominant CO2RR; decreases in cell voltage occur with the switch from the CO2RR to HER. Further, real time visual observations show that salt precipitation occurs during the CO2RR, whereas salt dissolution occurs during the HER. Slow flooding triggers the transition from the CO2RR to HER. A number of processes combine to slowly reduce the water content in the microporous layer, which triggers the transition back to the CO2RR.