Valorisation of Citrus Waste for Sustainable Synthesis of Carbon-Supported Copper Nanoparticles active in CO2 Electroreduction

Abstract

This study presents the development of a wet-chemical approach using microwave-assisted hydrothermal synthesis to produce carbon-supported Cu electrocatalysts for CO₂ conversion. Citrus peels are employed both as the carbon support precursor and as a reducing agent for Cu cations derived from various precursors, including chloride, nitrate and sulphate. Combined XPS and XRD analyses reveal that the resulting nanostructures consist of Cu/Cu₂O core shell nanoparticles, predominantly metallic in nature, with a C-overlayer and embedded within the carbon matrix. Our findings demonstrate that not only the type of the peel as earlier reported influences the initial structure of the electrocatalysts but also the nature of the anions. While the effect on the Cu phase is minimal, there is a significant impact of these on the structure of the carbon matrix. This is evidenced by the different ratio between the graphitic sp² component and the defective sp²/sp³ component, the latter being associated with higher ECSA values due to increased porosity. The superior performances of the orange peel-derived systems compared to the lemon peel-derived systems is attributed to the stabilization of the Cu phase during CO₂ reduction, facilitated by the characteristic C matrix. Notably, sulphate-derived electrocatalysts supported on the orange peel-derived C exhibits enhanced activity for CO2 reduction towards CO and methane, suggesting that the sample exhibits the optimal structural characteristics. This work highlights the potential of citrus waste, specifically orange peels, as a sustainable and cost-effective strategy to produce CO₂ reduction electrocatalysts. This approach offers a promising avenue for waste valorisation and the development of environmentally friendly CO₂ conversion technologies.