Synergistic effect of Cu-doped NiO for enhancing urea electrooxidation: Comparative electrochemical and DFT studies

In the present work, Cu-doped NiO is fabricated and synthesized using a microwave-assisted sol-gel method using different Ni and Cu precursors ratios supported on commercial graphite rod (G) and examined as an efficient electrocatalyst toward urea electrochemical oxidation (UEO). The morphology and chemical structure of the prepared electrocatalysts is confirmed by XRD, XPS, and SEM techniques. The catalytic activity of the prepared materials is measured and examined toward UEO as a function of current density and compared with different Ni-based catalysts in NaOH solution using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The oxidation current density of G/Ni0.9Cu0.1 reached 32 mA cm-2, and its onset potential of urea oxidation peak is shifted from 0.43 V (vs. Ag/AgCl) in NiO catalyst to 0.40 V (vs. Ag/AgCl) for G/Ni0.9Cu0.1. The charge transfer resistance for different modified surfaces at various conditions (e.g., urea concentration, electrolyte concentration, and oxidation potential) is measured using the electrochemical impedance spectroscopy (EIS). The CO tolerance is studied using the DFT method to prove the stability of the electrodes and the performance efficiency due to Cu atoms dopping into NiO crystal. The adsorption of CO is studied upon Cu-doped NiO and compared with pristine NiO alloy at different adsorption sites- top and hallow.