Copper is one of the most promising CO₂ reduction electrocatalysts, because it allows to reduce CO₂ to complex hydrocarbons with good efficiency, thus allowing to store renewable energies-generated electricity in the form of chemical energy of carbon-based fuels. Bulk polycrystalline copper, however, has unsatisfactory activity and requires high overpotentials for the reduction reaction. Oxide-derived copper (OD-Cu) catalyst are one of the most efficient way to increase the intrinsic activity of Cu: this class of materials have higher selectivity for complex hydrocarbons and longer stability. Moreover, their activity and selectivity are strongly affected by the morphology, which controls the mass transport of the reactants to the active sites and influences the local pH.

In this contribution, we study the influence of morphological and structural features of OD-Cu hierarchical nanostructured electrocatalysts on their CO₂ reduction activity and selectivity. We synthesize a nano-crystalline copper oxide (CuO_x) material, which exhibits a high availability of defective, under-coordinated surface sites granting a good reduction activity, exploiting Pulsed Laser Deposition (PLD) as synthesis method. We leverage on the advantages of this technique, which allows to finely tune the morphology and porosity features of the synthesized material, to control the aspect ratio, the nanostructuring and the pore distribution of the CuO_x nanostructures. With this approach, it is possible to evaluate the effect of the nanoscale morphological features on the overall catalytic activity of the OD-Cu material. Characterization of the CuO_x nanostructures reveals an amorphous matrix with embedded crystallites of CuO and Cu₂O, differently from other reported oxide-derived Cu catalysts. Electrochemical characterization of the CuO_x nanostructures shows a clear trend between synthesis parameters and electrochemical surface area.

CO₂ reduction performance of the oxide-derived Cu nanostructures is assessed through chronoamperometric measurements in aqueous electrolyte, showing for the best-performing catalyst remarkable FE at low applied overpotentials. A FE of 40% towards CH₄ is calculated by means of gas-chromatography, while through ¹H-NMR spectroscopy a total FE for liquid products in the 45-50% range is registered at -0.4 V_RHE. Moreover, the OD-Cu nanostructures shows good stability for at least one hour of prolonged electrochemical operation.

This contribution shows how the combined effect of a OD-Cu material with a highly-defective, metastable structure and a fine control over the catalyst morphology can represent an efficient way to enhance the activity of a Cu-derived CO₂ reduction catalyst.