Enhancement of Ethylene Faradaic Efficiency Using Ionic Liquid–Modified CuO/g-C₃N₄ Composite Catalysts for CO₂ Reduction

Overview

Introduction: The emission of carbon dioxide (CO₂) remains one of the most pressing environmental and climate challenges facing the world today. Electrochemical CO₂ reduction (CO₂RR) converts CO₂ into high-value chemical products, and the catalyst used during the process strongly influences energy efficiency and product selectivity. This study evaluated the performance of a novel composite catalyst CuO/g-C3N4/IL [CuO nanoparticles (NP) on graphitic carbon nitride (g-C3N4) modified with an ionic liquid (IL) coating] designed to optimize Faradaic efficiency (FE) for ethylene (C2H4) production. We hypothesized that the integration of CuO, g-C₃N₄, and an IL would produce a synergistic effect that enhances C₂H₄ selectivity during CO₂ reduction. The experiment results are then compared to benchmarks from other CuO-based catalysts. Procedure: The catalyst was synthesized through a three-stage process: 1) CuO NP were coated with [C10mim][NTf2] IL; 2) g-C3N4 nanosheets were produced through the thermal conversion of dicyandiamide; and 3) both components were then integrated and reduced under an Ar/H2 atmosphere at 200°C. CO₂RR was conducted in an H-cell reactor using a NaHCO3 electrolyte. The Gas Chromatography quantified gaseous products (CO, H2, CH4, and C2H4) across a potential range of -1.2V to -1.6V. The resulting FE values were compared to those from CuO in this study and those reported for CuO/g-C₃N₄ in the literature to assess the impact of the IL interface. Results: CuO/g-C₃N₄/IL demonstrated consistently, significantly higher FE_C₂H₄ than CuO across all the potential range (−1.2V, p<.05; -1.4V, p<.001; −1.6V, p<.001), with the greatest 60% enhancement observed at −1.2V. At this potential, CuO/g-C₃N₄/IL also showed a 92% improvement over literature-reported CuO/g-C₃N₄ benchmarks. Significant decreases in CH₄ production were observed at −1.2V and −1.4V, while no significant changes in H₂ production were detected across all tested potentials. Conclusion: The IL-modified composite enhances C₂H₄ selectivity by increasing local CO₂ concentration and promoting C–C coupling. Interfacial engineering with g-C₃N₄ and IL is an effective strategy for selective CO₂ reduction to ethylene. Future research should focus on investigating various IL structures to improve catalyst performance across a broader potential range.