Valorisation of citrus waste for sustainable synthesis of carbon-supported copper nanoparticles active in CO2 electroreduction

This study describes a microwave-assisted hydrothermal method to synthesise carbon-supported Cu-based electrocatalysts for CO2 conversion using citrus peels as both the carbon precursor and the reducing agent for Cu cations. XPS, TEM, and XRD analyses reveal the structural heterogeneity of the samples, resulting from a complex chemistry influenced by both the type of citrus peel used and the Cu salt precursor. As a result, mixed Cu/Cu2O nanoparticles form, which are immobilized on the surface or embedded within the carbon matrix. Orange peel-derived systems exhibit an optimal graphitic-to-defective carbon ratio, resulting in an optimal porosity, electron conduction, and Cu stabilisation, leading to superior CO2 reduction performance. A Cu sulphate-derived catalyst supported on orange peel-derived carbon yields the best performance for CO and methane production, shedding light on specific structural characteristics of the catalysts precursor state able to generate in situ an active phase with improved performance. This work demonstrates the potential of orange peel waste as a sustainable feedstock for the production of CO2 reduction electrocatalysts, offering a green strategy for waste valorisation and clean energy technologies.