The electrochemical behavior of a graphite anode in 2.4NaF/AlF 3 -0.05wt%Al 2 O 3 molten salt was investigated via cyclic voltammetry (CV) and chrono-electrochemical techniques. Four oxidation current peaks, located at 1.42, 2.5, 3.1, and 3.94 V vs. Al/Al 3+ , were observed in CV curves, which may be attributed to the formation of CO 2 , CF 4 , graphite fluoride ((CF) n ), and F 2 , respectively. The anode effect occurred when the potential exceeded 3.5 V. Meanwhile, the mechanism of the electrode reaction of CO 2 and (CF) n formation was confirmed to be irreversible charge transfer followed by a chemical reaction. Therefore, we confirmed that the passivation of the graphite anode was due to the formation of (CF) n on the electrode surface, blocking the mass transfer. According to the number of the charge transfer and the characteristics of the electrode reactions, we discuss detailed reaction pathways for CF 4 and (CF) n formation. In addition, the presence of the small quantity of C 2 F 6 in the anode gas is discussed.In the primary aluminum production by the Hall-Héroult process, cryolite-alumina molten salt and a carbon anode are employed. The cell reaction under normal conditions isThe exit gas from the electrolysis cell consists of a mixture of CO 2 and CO, and the secondary reactions between CO 2 and aluminum yield CO. 1 However, a cell malfunction, known as the anode effect (AE), can easily occur when the alumina content in the electrolyte is less than 1 wt%. The anode effect results in not only the generation of perfluorocarbons (PFCs) CF 4 and C 2 F 6 but also a high consumption of energy for a higher cell voltage. 2 Owing to the high global warming potentials of CF 4 and C 2 F 6 3 and the fact that the primary aluminum industry is the major anthropogenic source of CF 4 and C 2 F 6 , 4 the Environmental Protection Agency and the primary aluminum producers have established the Voluntary Aluminum Industrial Partnership (VAIP) with the goal of substantially reducing PFC emission. 5 To gain a better understanding of the mechanism of CF 4 and C 2 F 6 generation, the anodic behaviors of carbonaceous electrodes have been widely studied in recent decades. The traditional view mentioned that fluorine ions react with carbon anodes to directly generate CF 4 and C 2 F 6 during the anode effect. 2,6,7 The formation of CF 4 and C 2 F 6 can be expressed by the following reactions:Moreover, CF 4 and C 2 F 6 coming from the decomposition of COF 2 has been suggested. 8-11 COF 2 is considered an intermediate product prior to the anode effect, then, it decomposes to form CF 4 and C 2 F 6 . The reactions are described as 2Na 3 AlF 6 + Al 2 O 3 + 3C = 3COF 2 + 6NaF + 4Al E 1373K = 1.81 V [4] 2COF 2 = CO 2 + CF 4 lg K 1373K = −0.176 [5] 3COF 2 + 2C = 3CO + C 2 F 6 lg K 1373K = −1.351 [6]