Synthesis and Characterization of Cu-based Electrocatalysts for ECCO2R to C2/C2+ Products

The continuous growth of the global population is driving an ever-increasing energy demand. However, society remains dependent on petroleum-based infrastructure while grappling with the inherent intermittency of renewable energy sources, highlighting the urgent need for innovative solutions. In this context, mitigating ecosystem damage has become a key priority, with the carbon cycle emerging as a focal point of research. Carbon Capture and Sequestration (CCS) technologies, alongside Electrochemical CO₂ Reduction (ECCO₂R), offer a promising approach to transforming CO2 from a pollutant into a valuable resource. By reducing atmospheric CO₂ levels, this strategy addresses environmental concerns and repurposes CO₂ as a raw material for synthesizing chemicals and fuels. Among electrocatalytic materials, polycrystalline Cu stands out as the only metal capable of producing a variety of hydrocarbons and alcohols. However, its lack of selectivity toward specific product classes remains a significant limitation. In contrast, Copper(I) Oxide Cu₂O has been shown to exhibit superior selectivity for C₂/C₂+ products, making it a more promising candidate for targeted hydrocarbon production. This study aims to synthesize a Cu₂O nano-catalyst for ECCO₂R with enhanced selectivity toward C₂/C₂+ products. To that purpose, different synthesis routes have been explored, leveraging three distinct capping agents: Polyvinylpyrrolidone 40, Cetrimonium bromide, and Polyvinylpyrrolidone K30, to obtain diverse nanoparticle (NP) morphologies. The effect of silver deposition at varying concentrations on the Cu₂O NPs surface has also been investigated. Optimizing NPs morphology generates abundant oxygen vacancies, which increase local charge density, thereby improving CO₂ adsorption and activation. Moreover, the Ag deposition on Cu₂O NPs has enhanced the concentration of *CO on the catalyst surface. Thermodynamically and kinetically favorable *CO spillover from Ag to Cu sites promotes C–C coupling, improving selectivity toward C₂+ products. All synthesized NPs have been characterized by specific surface area, crystallite sizes, electrochemical surface area, composition, and morphology. Six have been tested as electrocatalysts in a flow-continuous cell with direct gas-phase humidified CO₂ injection at -50 mAcm-2. The working electrode was a half-membrane Electrode Assembly (half-MEA) with an anionic exchange membrane. Product selectivity has been analyzed and correlated with the characterization results. The results revealed that the Cu₂O with Ag 1 %mol sample exhibits a significantly higher Faradaic Efficiency (FE) for C₂ and C₂+ products (34.59% ethylene 12.45% ethanol and 6.30% 1-propanol at -50 mA cm-2). This result fits with the highest average crystallite size (43.7 nm), the smallest average pore width (109.8 nm), the highest double-layer capacitance (1.78 µF, indicating superior electrocatalytic activity), and the highest NPs mean diameter (137 nm) with spherical morphology. However, increasing the Ag content beyond 1 %mol appears to negatively impact performance, as evidenced by the sharp decline in FEs observed in Cu₂O with Ag 2%mol. The most promising samples have been deposited on a gas diffusion layer (GDL) with a microporous layer, to enhance CO₂ diffusivity and suppress hydrogen production. However, as the silver amount increases, the decreasing trend in C2 and C2+ selectivity is maintained, highlighting the detrimental effect of excessive Ag deposition.