Study and optimization of glycerol electro-oxidation on a Cu2O catalyst: experimental approach and modeling via response surface methodology based on box–behnken design

Abstract

This study presents the design and optimization of copper(I) oxide (Cu₂O) thin films as electrocatalysts for glycerol electro-oxidation in alkaline environments. Cu₂O films were synthesized via electrodeposition on copper substrates using a citric acid-based electrolyte, chosen for its low toxicity and complexing properties. The study systematically optimized key deposition parameters such as temperature (55–75 °C), stirring rate (0–300 r min⁻¹), scan rate (10–100 mV s⁻¹), and precursor concentration (0.05–0.07 mol L⁻¹) using Response Surface Methodology (RSM) coupled with a Box-Behnken Design (BBD). The optimized conditions (75 °C, 300 r min⁻¹, 55 mV s⁻¹, 0.06 mol L⁻¹) resulted in the formation of a homogeneous, adherent Cu₂O film with a thickness of 420.69 nm, predicted by a statistically validated quadratic model (R² = 0.9768). Structural analysis by X-ray diffraction (XRD) confirmed the formation of pure Cu₂O in the cubic cuprite phase. Optical microscopy revealed a smooth and uniform surface, which is vital for electrocatalytic applications. Electrochemical testing showed that the Cu₂O film stabilized the open circuit potential at -0.1150 V vs. Ag/AgCl, indicating surface passivation. Cyclic voltammetry (CV) in an alkaline glycerol solution (0.5 mol L⁻¹) exhibited two oxidation peaks at − 0.01 V and + 0.23 V vs. Ag/AgCl, confirming the electrocatalytic activity of the Cu₂O film. Chronoamperometric measurements at + 0.2 V vs. Ag/AgCl for 40 min revealed a stable current density (~ 2.41 mA) for the thicker film, indicating improved electrocatalytic performance due to a larger electroactive surface area. These results demonstrate that Cu₂O thin films, synthesized under optimized conditions, exhibit promising catalytic activity for glycerol electro-oxidation, offering an alternative to noble metal-based catalysts.