Effect of acid on passivation of a copper electrode in LiCF3SO3/propylene carbonate in underpotential region

The electrochemical behaviour of a copper electrode is examined using microelectrode (diameter=0.025 mm) techniques over a wide potential range (+3.5 to −0.2 V vs. Li/Li+) in LiCF3SO3 which contains propylene carbonate (PC). Cyclic voltammetry and differential pulse voltammetry suggest that water may be the cause of passivation of a copper electrode. Small amounts of strong acid can prevent this passivation by changing the reduction mechanism of oxygen and water in the underpotential region. X-ray photoelectron spectroscopic analysis reveals that lithium compounds precipitate on copper, even in the underpotential region, when no acid is added to the organic solution.