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The novel use of p-nitrophenyldiazonium tetrafluoroborate salt (GG salt) as a protectant that is electrochemically grafted onto carbon steel has been investigated in 0.05 mol L HSO and 5 wt% NaCl solutions using various corrosion monitoring techniques, such as electrochemical impedance spectroscopy, potentiodynamic polarisation, infrared spectra and scanning electron microscopy measurements. The electrochemical study reveals that this compound is a mixed inhibitor that predominantly controls the cathodic reaction. The surface-grafted film decreases the double-layer capacitance and obviously increases the charge transfer resistance relative to a bare carbon electrode. The values of inhibition effect remain nearly unchanged with an increase in temperature range of 298-318 K. The aryl diazonium is covalently bonded on the steel surface, causing a slight decrease in the apparent activation energy. Overall, the surface-grafted films exhibit excellent inhibition performance in acid and saline solutions within the studied temperature range. [ABSTRACT FROM AUTHOR]