This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Copper sulfide (CuS) catalysts continuously reconstruct their surface during electrochemical CO2 reduction, reports a study from the Institute of Science Tokyo, Japan. By uncovering the mechanism behind the dynamic surface changes that occur during potential-step electrolysis, the researchers revealed how sulfur and oxygen play distinct roles in catalyst activity and product selectivity, paving the way for improved CO2 conversion technologies.
Electrochemical carbon dioxide (CO₂) reduction offers a promising way to convert greenhouse gas emissions into valuable chemicals using renewable electricity. Among the many catalysts under investigation, copper sulfide (CuS) has attracted considerable attention because of its abundance, low cost and ability to convert CO₂ into useful products. A technique that has gained increasing attention is the potential-step method.
In this method, the catalyst is repeatedly exposed to alternating negative and positive electrical potentials. This method has been shown to improve the selectivity of CO₂ reduction in CuS catalysts; however, the surface transformations responsible for this enhanced performance have remained largely unknown. To address this question, a research team led by associate professor Akira Yamaguchi from the Department of Materials Science and Engineering, Institute of Science Tokyo (Science Tokyo), Japan, along with graduate student Hisanobu Taga and Professor Masahiro Miyauchi from Science Tokyo, investigated how the surface of CuS evolves during potential-step electrochemical CO₂ reduction.
The study was published in Materials Advances on Aug. 18, 2026. Their findings reveal that the catalyst undergoes continuous structural transformations throughout the reaction, with sulfur and oxygen playing distinct yet complementary roles in controlling product formation. "We sought to uncover how the catalyst surface changes during the potential-step process and how these transformations influence the reaction pathway," says Yamaguchi.
The researchers combined characterization techniques like X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and in situ Fourier transform infrared spectroscopy to monitor the catalyst before, during and after electrochemical reactions. This analysis revealed that applying a negative potential partially reduced CuS, causing some sulfur atoms to leave the surface and generate metallic copper (Cu⁰) active sites. These active sites enable CO₂ to adsorb and undergo conversion into key reaction intermediates, ultimately producing compounds such as formic acid.
Similarly, when a positive potential was applied, oxygen-containing species from the electrolyte reacted with these copper sites to form copper(I) oxide (Cu₂O). Returning to the negative potential led to the reduction of the oxide back to metallic copper, resulting in a continuous cycle of catalyst reconstruction throughout the reaction. This dynamic behavior contrasts with the conventional assumption that catalyst surfaces remain largely unchanged during electrochemical operation.
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