According to the electrochemical analysis, the corrosion inhibition efficiency of 5-methyl-lH-benzotriazole （m-BTA） is higher than that of benzotrizaole （BTA）. The inhibition capability of the m-BTA passive film formed in hydroxyethylidenediphosphonic acid （HEDP） electrolyte containing both m-BTA and chloride ions is superior to that formed in m-BTA-alone electrolyte, even at a high anodic potential. The results of electrical impedance spectroscopy, nano-scratch experiments and energy dispersive analysis of X-ray （EDAX） indicate that the enhancement of m-BTA inhibition capability may be due to the increasing thickness of passive film. Furthermore, X-ray photoelectron spectrometry （XPS） analysis indicates that the increase in passive film thickness can be attributed to the incorporation of C1 into the m-BTA passive film and the formation of [Cu（I）CI（rn-BTA）], polymer film on Cu surface. Therefore, the introduction of C1- into m-BTA-containing HEDP electrolyte is effective to enhance the passivation capability of m-BTA passive film, thus extending the operating potential window.
