Abstract:

The ever-increasing carbon dioxide (CO₂) emissions caused by excessive fossil fuel consumption induce environmental issues such as global warming. To overcome this, the electrocatalytic CO₂ reduction (ECR) under ambient conditions offers an appealing approach for converting CO₂ to value-added chemicals and realizing a closed carbon loop. Among the ECR products, ethylene (C₂H₄), an important building block for plastics and other chemicals, has attracted considerable attention owing to its compatibility with existing infrastructure and the promising substitution of industrial steam cracking. In recent years, numerous efforts have been devoted to developing highly active and selective catalysts for converting CO₂ to C₂H₄, with most studies having focused on Cu-based materials. Despite the significant advancements made to date, the development of the ECR-to-C₂H₄ process is still hindered by the lack of suitable catalysts that can effectively activate CO₂ and strengthen the surface binding of *CO and *COH species. In this study, an amorphous copper oxide (CuO_x) nanofilm that is rich in oxygen vacancies was prepared via a facile vacuum evaporation method for the efficient electrocatalytic conversion of CO₂ to C₂H₄. It was expected that the nano-scale electrode thickness would greatly accelerate charge- and mass-transfer during CO₂ electrolysis. Moreover, the introduction of oxygen vacancies favored the adsorption of CO₂ and intermediates. As a result, in a typical H-cell, the synthesized defective catalyst delivered a maximum Faradaic efficiency of 85 ± 3% at −1.3 V versus the reversible hydrogen electrode and maintained a stable C₂H₄ selectivity over 48 h in a 0.1 M potassium bicarbonate solution. Interestingly, the performance observed with the synthesized electrocatalyst in this study is comparable with that of state-of-the-art Cu-based ECR catalysts. Additional structural and chemical characterizations confirmed the robust nature of the as-prepared catalyst. Moreover, when the catalyst was utilized in a membrane electrode assembly cell, it achieved a maximum C₂H₄ partial current density of approximately 115.4 mA∙cm⁻² at a cell voltage of −1.95 V and Faradaic efficiency of 78 ± 2% at a cell voltage of −1.75 V. Furthermore, theoretical and experimental analyses revealed that oxygen defects not only favored CO₂ adsorption but also enabled strong affinities for *CO and *COH intermediates, which synergistically contributed to a high selectivity for C₂H₄ formation. We believe that our present work will motivate the exploration of amorphous Cu-based materials for achieving efficient CO₂-to-C₂H₄ electrolysis and be a guide towards fundamentally understanding the mechanism of catalytic CO₂ reduction.

Key words: CO₂ fixation, C₂ product, Electrocatalysis, Amorphous catalyst, Cu oxide