Recently, Prof. ZENG Jie’s group from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, collaborating with Prof. XIA Chuan and ZHENG Tingting’s team from the University of Electronic Science and Technology of China, developed an undercoordinated Cu nanodots catalyst to achieve acetylene (C₂H₂) semihydrogenation with high intrinsic activity and efficiency. The study was published in Nature Communications. 

Ethylene (C₂H₄) is a prominent material in chemical industry. Normally, the industrial production process of C₂H₄ unavoidably produces 0.5%-3% C₂H₂ byproduct that irreversibly poisons the Ziegler-Natta catalysts, resulting in a decline in activity. Therefore, it is important to remove the C₂H₂ impurities in C₂H₄ production. The traditional thermocatalytic semihydrogenation of C₂H₂ requires high temperature, high pressure and expensive palladium-based catalyst, which limit its further development. 

The decreasing cost of electricity has motivated the development of electrocatalytic C₂H₂ semihydrogenation (EASH) using Cu-based catalysts as an alternative. However, previous Cu-based catalysts still suffer from side reactions, which results in unsatisfactory purification.  

To solve this problem, the researchers synthesized undercoordinated Cu nanodots (Cu NDs) as catalysts by in situ reduction. When tested for activity under pure C₂H₂ flow, the undercoordinated Cu NDs achieved a Faradaic efficiency of over 90% under a wide range of current density, reaching a peak of 95.6% at a current density of -350mA·cm^-2. Additionally, in situ spectroscopy revealed a lower energy barrier for undercoordinated Cu NDs catalysts. 

Membrane electrode assembly (MEA) reactors have the advantages of low resistance, low energy consumption and compact configuration. Therefore, the researchers designed an MEA-type-two-electrode reactor for continuous generation of polymer-grade C₂H₄.

In the performance evaluation test, a 25 cm² MEA reactor could completely convert 0.5% C₂H₂ to C₂H₄ at different flow rates from 10 to 50 standard cubic centimeter per minute (sccm). With the increase of the flow rate, the selectivity of C₂H₄ showed an upward trend. The researchers managed to continuously synthesize polymer-grade C₂H₄ for 130 hours under a flow rate of 50 sccm with negligible performance decay (residual C₂H₂ less than 1 part per million, cell voltage maintained at -1.89V). 

This work realized highly efficient EASH to produce polymer-grade C₂H₄ through catalyst development, reaction mechanism study and reactor design, providing prospects for future development of electrocatalytic C₂H₄ purification.