The corrosion inhibition effect of aryl pyrazolo pyridines on copper in hydrochloric acid system: computational and electrochemical studies

The inhibition effect of three aryl pyrazole pyridine derivatives namely: 3-methyl-6-oxo-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (APP I), 3-methyl-6-oxo-4-(3-phenoxyphenyl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (APP II) and 3-methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5 carbonitrile (APP III) against the corrosion of copper in 0.5 M HCl solution has been systematically investigated by electrochemical impedance spectroscopy, potentiodynamic polarization measurements and quantum chemical methods. A good correlation between the computed energy gap, omega E, data and the experimental inhibition efficiencies was found. Potentiodynamic polarization measurement results indicate that all three APPs derivatives are cathodic type inhibitors. Among the studied compounds, APP I exhibited the best inhibition activity 92.3% at 1.59 mmol/L. The scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy confirmed the presence of inhibitors on the copper surface.