Y-Doped CuS Promotes Selective Electroreduction of CO₂ to Ethanol

The carbon dioxide reduction reaction (CO₂RR) offers a promising route for sustainable energy conversion. However, achieving high selectivity toward targeted C-C products such as ethanol remains a significant challenge. This limitation stems from the structural complexity and design constraints of efficient Cu-based catalysts, as well as uncertainties regarding the nature of active sites. In this study, we present a rare-earth doping strategy in which yttrium (Y) facilitates the formation of amorphous, low-valent Cu species - identified as key contributors to ethanol selectivity. Using this Y-CuS catalyst, we demonstrate direct ethanol synthesis from CO₂ at a current density of 400 mA cm^-2, achieving a Faraday efficiency of 52%. Notably, when the ethanol-producing current density exceeds 200 mA cm^-2, the energy efficiency reaches 23.8%. In situ infrared spectroscopy-mass spectrometry, combined with time-resolved absorption measurements, reveals that Y incorporation into the Cu-S matrix enhances the generation of ethanol-related intermediates by increasing the density of active sites. Complementary in situ X-ray diffraction (XRD) and fluorescence spectroscopy further confirm that the amorphous low-valent Cu species serve as the primary active sites for selective ethanol production, which is further supported by X-ray spectroscopy and ab initio molecular dynamics simulations. Our findings establish a new catalyst design strategy, demonstrating that rare-earth doping can induce the formation of highly active amorphous Cu sites. This approach offers a sustainable and generalizable pathway for efficient CO₂ conversion to ethanol and potentially other value-added products.