Copper sulfide (CuS) catalysts continuously reconstruct their surface during electrochemical CO 2 reduction, reports a study from 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 CO 2 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 a graduating school student Hisanobu Taga, and Professor Masahiro Miyauchi from Science Tokyo, investigated how the surface of CuS evolves during the Potential-Step electrochemical CO₂ reduction. The study was published in Materials Advances on August 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). Now, 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.
The study also explains how individual elements contribute to catalytic performance by comparing CuS with metallic copper, copper in the presence of sulfur ions, and Cu₂O. The experiments also revealed that, based on location, sulfur plays two different roles. On the catalytic surface sulfur promotes hydrogen adsorption, facilitating CO₂ reduction, and within the catalyst it stabilizes key carbon monoxide intermediates. This leads to formation of formic acid while suppressing competing hydrocarbon formation. Meanwhile oxygen incorporated into the catalyst during the positive potential phase generates neighboring Cu⁰/Cu⁺ sites that promote carbon–carbon bond formation, leading the selectivity towards multi-carbon products.
" Our results show that sulfur and oxygen are not passive components of the catalyst. Instead, they actively reshape the catalyst surface and direct the reaction toward different products," explains Yamaguchi.
Thus, the study provides valuable mechanistic insights for the design of next-generation electrocatalysts by revealing dynamic reconstruction of CuS during the Potential-Step electrolysis. Rather than focusing solely on catalyst composition, future research may exploit controlled surface transformations as per catalytic activity and selectivity adaptions. These strategies could contribute to more efficient CO 2 conversion technologies, which could lead to the transformation of greenhouse gases into useful chemicals, while supporting sustainable manufacturing and carbon recycling in the future.
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About Institute of Science Tokyo (Science Tokyo)
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”
DOI: https://doi.org/10.1039/d6ma00736h
Materials Advances
Experimental study
Not applicable
Investigation of Anion Role during Electrochemical CO2 Reduction on Copper Sulfide (CuS) by Potential-Step Method
18-Aug-2026
There are no conflicts to declare